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学习笔记(二)--->《Java 8编程官方参考教程（第9版）.pdf》:第七章到九章学习笔记

注：本文声明事项。

本博文整理者：刘军

本博文出自于：《Java8 编程官方参考教程》一书

声明：1:转载请标注出处。本文不得作为商业活动。若有违本之，则本人不负法律责任。违法者自负一切法律责任。

2: 本书对应的jdk为 jdk8版本

3：因为内容容量太大，编辑器无法承受于是给拆分了以下版本：

《Java 8编程官方参考教程（第9版）.pdf》学习笔记（一）--->第一章到六章学习笔记：讲：java的历史和演变、Java概述、数据类型、变量和数组、运算符、控制语句、类等内容

《Java 8编程官方参考教程（第9版）.pdf》学习笔记(二)--->第七章到九章学习笔记：讲：java 方法、继承详解、包和接口

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《Java 8编程官方参考教程（第9版）》pdf 下载地址：http://pan.baidu.com/s/1o7Zp3Mq 密码： 33cf

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第7章方法和类的深入分析

7.1 重载方法

  1 package Chap7;
  2 
  3 /**
  4  * Demonstrate method overloading.
  5  *
  6  * @ClassName: OverloadDemo
  7  * @Description:
  8  * @author 刘军/shall_liu (1136808529@qq.com)
  9  * @date 2017年9月14日 上午12:15:21
 10  *
 11  */
 12 class OverloadDemo {
 13 	void test() {
 14 		System.out.println("No parameters");
 15 	}
 16 
 17 	// Overload test for one integer parameter.
 18 	void test(int a) {
 19 		System.out.println("a: " + a);
 20 	}
 21 
 22 	// Overload test for two integer parameters.
 23 	void test(int a, int b) {
 24 		System.out.println("a and b: " + a + " " + b);
 25 	}
 26 
 27 	// overload test for a double parameter
 28 	double test(double a) {
 29 		System.out.println("double a: " + a);
 30 		return a * a;
 31 	}
 32 }
 33 
 34 
 35 package Chap7;
 36 
 37 /**
 38  *
 39  * @ClassName: Overload
 40  * @Description:
 41  * @author 刘军/shall_liu (1136808529@qq.com)
 42  * @date 2017年9月14日 下午11:35:25
 43  *
 44  */
 45 class Overload {
 46 	public static void main(String args[]) {
 47 		OverloadDemo ob = new OverloadDemo();
 48 		double result;
 49 
 50 		// call all versions of test()
 51 		ob.test();
 52 		ob.test(10);
 53 		ob.test(10, 20);
 54 		result = ob.test(123.25);
 55 		System.out.println("Result of ob.test(123.25): " + result);
 56 	}
 57 }
 58 //其运行结果为：
 59 No parameters
 60 a: 10
 61 a and b: 10 20
 62 double a: 123.25
 63 Result of ob.test(123.25): 15190.5625
 64 
 65 
 66 
 67

View Code

  1 package Chap7;
  2 
  3 /**
  4  * Demonstrate method overloading.
  5  *
  6  * @ClassName: OverloadDemo
  7  * @Description:
  8  * @author 刘军/shall_liu (1136808529@qq.com)
  9  * @date 2017年9月14日 上午12:15:21
 10  *
 11  */
 12 class OverloadDemo {
 13 	void test() {
 14 		System.out.println("No parameters");
 15 	}
 16 
 17 	// Overload test for two integer parameters.
 18 	void test(int a, int b) {
 19 		System.out.println("a and b: " + a + " " + b);
 20 	}
 21 
 22 	// overload test for a double parameter and return type
 23 	void test(double a) {
 24 		System.out.println("Inside test(double) a: " + a);
 25 	}
 26 }
 27 
 28 package Chap7;
 29 
 30 /**
 31  *
 32  * @ClassName: Overload
 33  * @Description:
 34  * @author 刘军/shall_liu (1136808529@qq.com)
 35  * @date 2017年9月14日 下午11:35:25
 36  *
 37  */
 38 class Overload {
 39 	public static void main(String args[]) {
 40 		OverloadDemo ob = new OverloadDemo();
 41 		int i = 88;
 42 
 43 		ob.test();
 44 		ob.test(10, 20);
 45 
 46 		ob.test(i); // this will invoke test(double)
 47 		ob.test(123.2); // this will invoke test(double)
 48 	}
 49 }
 50 //其运行结果为：
 51 No parameters
 52 a and b: 10 20
 53 Inside test(double) a: 88.0
 54 Inside test(double) a: 123.2
 55

View Code

7.1.1 重载构造函数

  1 package Chap7;
  2 
  3 /**
  4  *
  5 * @ClassName: Box
  6 * @Description:  重载构造器
  7 * @author  刘军/shall_liu (1136808529@qq.com)
  8 * @date 2017年9月14日 下午11:47:01
  9 *
 10  */
 11 class Box {
 12 	double width;
 13 	double height;
 14 	double depth;
 15 
 16 	// This is the constructor for Box.
 17 	Box(double w, double h, double d) {
 18 		width = w;
 19 		height = h;
 20 		depth = d;
 21 	}
 22 
 23 	// compute and return volume
 24 	double volume() {
 25 		return width * height * depth;
 26 	}
 27 }

View Code

  1 package Chap7;
  2 
  3 /**
  4  *
  5  * @ClassName: Box
  6  * @Description: 重载构造器
  7  * Here, Box defines three constructors to initialize the dimensions of a box
  8  * various ways.
  9  * @author 刘军/shall_liu (1136808529@qq.com)
 10  * @date 2017年9月14日 下午11:47:01
 11  *
 12  */
 13 class Box {
 14 	double width;
 15 	double height;
 16 	double depth;
 17 
 18 	// constructor used when all dimensions specified
 19 	Box(double w, double h, double d) {
 20 		width = w;
 21 		height = h;
 22 		depth = d;
 23 	}
 24 
 25 	// constructor used when no dimensions specified
 26 	Box() {
 27 		width = -1; // use -1 to indicate
 28 		height = -1; // an uninitialized
 29 		depth = -1; // box
 30 	}
 31 
 32 	// constructor used when cube is created
 33 	Box(double len) {
 34 		width = height = depth = len;
 35 	}
 36 
 37 	// compute and return volume
 38 	double volume() {
 39 		return width * height * depth;
 40 	}
 41 }
 42 
 43 
 44 
 45 package Chap7;
 46 
 47 /**
 48  *
 49 * @ClassName: OverloadCons
 50 * @Description:  重载构造器
 51 * @author  刘军/shall_liu (1136808529@qq.com)
 52 * @date 2017年9月14日 下午11:49:30
 53 *
 54  */
 55 
 56 class OverloadCons {
 57 	public static void main(String args[]) {
 58 		// create boxes using the various constructors
 59 		Box mybox1 = new Box(10, 20, 15);
 60 		Box mybox2 = new Box();
 61 		Box mycube = new Box(7);
 62 
 63 		double vol;
 64 
 65 		// get volume of first box
 66 		vol = mybox1.volume();
 67 		System.out.println("Volume of mybox1 is " + vol);
 68 
 69 		// get volume of second box
 70 		vol = mybox2.volume();
 71 		System.out.println("Volume of mybox2 is " + vol);
 72 
 73 		// get volume of cube
 74 		vol = mycube.volume();
 75 		System.out.println("Volume of mycube is " + vol);
 76 	}
 77 }
 78 
 79 //其运行结果为：
 80 Volume of mybox1 is 3000.0
 81 Volume of mybox2 is -1.0
 82 Volume of mycube is 343.0
 83 
 84 
 85

View Code

7.2 将对象用作参数

  1 class PassOb {
  2   public static void main(String args[]) {
  3     Test ob1 = new Test(100, 22);
  4     Test ob2 = new Test(100, 22);
  5     Test ob3 = new Test(-1, -1);
  6 
  7     System.out.println("ob1 == ob2: " + ob1.equalTo(ob2));
  8 
  9     System.out.println("ob1 == ob3: " + ob1.equalTo(ob3));
 10   }
 11 }
 12 
 13 package Chap7;
 14 
 15 /**
 16  * Objects may be passed to methods.
 17  *
 18  * @ClassName: Test
 19  * @Description:
 20  * @author 刘军/shall_liu (1136808529@qq.com)
 21  * @date 2017年9月14日 下午11:52:55
 22  *
 23  */
 24 class Test {
 25 	int a, b;
 26 
 27 	Test(int i, int j) {
 28 		a = i;
 29 		b = j;
 30 	}
 31 
 32 	// return true if o is equal to the invoking object
 33 	boolean equalTo(Test o) {
 34 		if (o.a == a && o.b == b)
 35 			return true;
 36 		else
 37 			return false;
 38 	}
 39 }
 40 //其运行结果为：
 41 ob1 == ob2: true
 42 ob1 == ob3: false
 43

View Code

  1 package Chap7;
  2 
  3 /**
  4  * Here, Box allows one object to initialize another.
  5  *
  6  * @ClassName: Box
  7  * @Description:
  8  * @author 刘军/shall_liu (1136808529@qq.com)
  9  * @date 2017年9月15日 上午12:00:54
 10  *
 11  */
 12 
 13 class Box {
 14 	double width;
 15 	double height;
 16 	double depth;
 17 
 18 	// construct clone of an object
 19 	Box(Box ob) { // pass object to constructor
 20 		width = ob.width;
 21 		height = ob.height;
 22 		depth = ob.depth;
 23 	}
 24 
 25 	// constructor used when all dimensions specified
 26 	Box(double w, double h, double d) {
 27 		width = w;
 28 		height = h;
 29 		depth = d;
 30 	}
 31 
 32 	// constructor used when no dimensions specified
 33 	Box() {
 34 		width = -1; // use -1 to indicate
 35 		height = -1; // an uninitialized
 36 		depth = -1; // box
 37 	}
 38 
 39 	// constructor used when cube is created
 40 	Box(double len) {
 41 		width = height = depth = len;
 42 	}
 43 
 44 	// compute and return volume
 45 	double volume() {
 46 		return width * height * depth;
 47 	}
 48 }
 49 
 50 package Chap7;
 51 
 52 /**
 53  *
 54  * @ClassName: OverloadCons2
 55  * @Description:
 56  * @author 刘军/shall_liu (1136808529@qq.com)
 57  * @date 2017年9月15日 上午12:01:21
 58  *
 59  */
 60 class OverloadCons2 {
 61 	public static void main(String args[]) {
 62 		// create boxes using the various constructors
 63 		Box mybox1 = new Box(10, 20, 15);
 64 		Box mybox2 = new Box();
 65 		Box mycube = new Box(7);
 66 
 67 		Box myclone = new Box(mybox1);
 68 
 69 		double vol;
 70 
 71 		// get volume of first box
 72 		vol = mybox1.volume();
 73 		System.out.println("Volume of mybox1 is " + vol);
 74 
 75 		// get volume of second box
 76 		vol = mybox2.volume();
 77 		System.out.println("Volume of mybox2 is " + vol);
 78 
 79 		// get volume of cube
 80 		vol = mycube.volume();
 81 		System.out.println("Volume of cube is " + vol);
 82 
 83 		// get volume of clone
 84 		vol = myclone.volume();
 85 		System.out.println("Volume of clone is " + vol);
 86 	}
 87 }
 88 
 89 
 90 //其运行结果为：
 91 Volume of mybox1 is 3000.0
 92 Volume of mybox2 is -1.0
 93 Volume of cube is 343.0
 94 Volume of clone is 3000.0
 95 
 96 
 97

View Code

7.3 参数传递的深入分析

  1 package Chap7;
  2 
  3 /**
  4  * Objects may be passed to methods.
  5  *
  6  * @ClassName: Test
  7  * @Description:
  8  * @author 刘军/shall_liu (1136808529@qq.com)
  9  * @date 2017年9月14日 下午11:52:55
 10  *
 11  */
 12 // Simple Types are passed by value.
 13 class Test {
 14 	void meth(int i, int j) {
 15 		i *= 2;
 16 		j /= 2;
 17 	}
 18 }
 19 
 20 package Chap7;
 21 
 22 class CallByValue {
 23 	public static void main(String args[]) {
 24 		Test ob = new Test();
 25 		int a = 15, b = 20;
 26 
 27 		System.out.println("a and b before call: " + a + " " + b);
 28 
 29 		ob.meth(a, b);
 30 
 31 		System.out.println("a and b after call: " + a + " " + b);
 32 	}
 33 }
 34 
 35 //其运行结果为：、
 36 a and b before call: 15 20
 37 a and b after call: 15 20
 38 
 39

View Code

  1 package Chap7;
  2 
  3 /**
  4  * Objects are passed through their references.
  5  *
  6  * @ClassName: Test
  7  * @Description:
  8  * @author 刘军/shall_liu (1136808529@qq.com)
  9  * @date 2017年9月14日 下午11:52:55
 10  *
 11  */
 12 
 13 class Test {
 14 	int a, b;
 15 
 16 	Test(int i, int j) {
 17 		a = i;
 18 		b = j;
 19 	}
 20 
 21 	// pass an object
 22 	void meth(Test o) {
 23 		o.a *= 2;
 24 		o.b /= 2;
 25 	}
 26 }
 27 
 28 
 29 package Chap7;
 30 
 31 /**
 32  *
 33  * @ClassName: PassObjRef
 34  * @Description:
 35  * @author 刘军/shall_liu (1136808529@qq.com)
 36  * @date 2017年9月15日 上午12:10:14
 37  *
 38  */
 39 class PassObjRef {
 40 	public static void main(String args[]) {
 41 		Test ob = new Test(15, 20);
 42 
 43 		System.out.println("ob.a and ob.b before call: " + ob.a + " " + ob.b);
 44 
 45 		ob.meth(ob);
 46 
 47 		System.out.println("ob.a and ob.b after call: " + ob.a + " " + ob.b);
 48 	}
 49 }
 50 
 51 //其运行结果为；
 52 ob.a and ob.b before call: 15 20
 53 ob.a and ob.b after call: 30 10
 54

View Code

7.4 返回对象

  1 package Chap7;
  2 
  3 /**
  4  * Objects are passed through their references.
  5  *
  6  * @ClassName: Test
  7  * @Description:
  8  * @author 刘军/shall_liu (1136808529@qq.com)
  9  * @date 2017年9月14日 下午11:52:55
 10  *
 11  */
 12 
 13 class Test {
 14 	int a, b;
 15 
 16 
 17 	public Test() {
 18 	}
 19 
 20 	Test(int i) {
 21 		a = i;
 22 	}
 23 
 24 	Test(int i, int j) {
 25 		a = i;
 26 		b = j;
 27 	}
 28 
 29 	// pass an object
 30 	void meth(Test o) {
 31 		o.a *= 2;
 32 		o.b /= 2;
 33 	}
 34 
 35 	Test incrByTen() {
 36 		Test temp = new Test(a + 10);
 37 		return temp;
 38 	}
 39 }
 40 
 41 
 42 
 43 package Chap7;
 44 
 45 class RetOb {
 46 	public static void main(String args[]) {
 47 		Test ob1 = new Test(2);
 48 		Test ob2;
 49 
 50 		ob2 = ob1.incrByTen();
 51 		System.out.println("ob1.a: " + ob1.a);
 52 		System.out.println("ob2.a: " + ob2.a);
 53 
 54 		ob2 = ob2.incrByTen();
 55 		System.out.println("ob2.a after second increase: " + ob2.a);
 56 	}
 57 }
 58 
 59 //
 60 ob1.a: 2
 61 ob2.a: 12
 62 ob2.a after second increase: 22
 63 
 64 
 65

View Code

7.5 递归

  1 package Chap7;
  2 
  3 //A simple example of recursion.
  4 class Factorial {
  5 	// this is a recusive function
  6 	int fact(int n) {
  7 		int result;
  8 
  9 		if (n == 1)
 10 			return 1;
 11 		result = fact(n - 1) * n;
 12 		return result;
 13 	}
 14 }
 15 
 16 
 17 package Chap7;
 18 
 19 class Recursion {
 20 	public static void main(String args[]) {
 21 		Factorial f = new Factorial();
 22 
 23 		System.out.println("Factorial of 3 is " + f.fact(3));
 24 		System.out.println("Factorial of 4 is " + f.fact(4));
 25 		System.out.println("Factorial of 5 is " + f.fact(5));
 26 	}
 27 }
 28 //
 29 
 30 
 31 Factorial of 3 is 6
 32 Factorial of 4 is 24
 33 Factorial of 5 is 120
 34

View Code

  1 package Chap7;
  2 
  3 //Another example that uses recursion.
  4 
  5 class RecTest {
  6 	int values[];
  7 
  8 	RecTest(int i) {
  9 		values = new int[i];
 10 	}
 11 
 12 	// display arrary -- recursively
 13 	void printArray(int i) {
 14 		if (i == 0)
 15 			return;
 16 		else
 17 			printArray(i - 1);
 18 		System.out.println("[" + (i - 1) + "] " + values[i - 1]);
 19 	}
 20 }
 21 
 22 package Chap7;
 23 
 24 class Recursion2 {
 25 	public static void main(String args[]) {
 26 		RecTest ob = new RecTest(10);
 27 		int i;
 28 
 29 		for (i = 0; i < 10; i++)
 30 			ob.values[i] = i;
 31 
 32 		ob.printArray(10);
 33 	}
 34 }
 35 
 36 //
 37 [0] 0
 38 [1] 1
 39 [2] 2
 40 [3] 3
 41 [4] 4
 42 [5] 5
 43 [6] 6
 44 [7] 7
 45 [8] 8
 46 [9] 9
 47 
 48

View Code

7.6 访问控制

  1 package Chap7;
  2 
  3 /* This program demonstrates the difference between
  4 public and private.
  5 */
  6 class Test {
  7 	int a; // default access
  8 	public int b; // public access
  9 	private int c; // private access
 10 
 11 	// methods to access c
 12 	void setc(int i) { // set c's value
 13 		c = i;
 14 	}
 15 
 16 	int getc() { // get c's value
 17 		return c;
 18 	}
 19 }
 20 
 21 
 22 package Chap7;
 23 
 24 class AccessTest {
 25 	public static void main(String args[]) {
 26 		Test ob = new Test();
 27 
 28 		// These are OK, a and b may be accessed directly
 29 		ob.a = 10;
 30 		ob.b = 20;
 31 
 32 		// This is not OK and will cause an error
 33 		// ob.c = 100; // Error!
 34 
 35 		// You must access c through its methods
 36 		ob.setc(100); // OK
 37 
 38 		System.out.println("a, b, and c: " + ob.a + " " + ob.b + " " + ob.getc());
 39 	}
 40 }
 41 //
 42 
 43 a, b, and c: 10 20 100
 44 
 45 
 46

View Code

  1 package Chap7;
  2 
  3 //This class defines an integer stack that can hold 10 values. 
  4 class Stack {
  5 	/*
  6 	 * Now, both stck and tos are private. This means that they cannot be
  7 	 * accidentally or maliciously altered in a way that would be harmful to the
  8 	 * stack.
  9 	 */
 10 	private int stck[] = new int[10];
 11 	private int tos;
 12 
 13 	// Initialize top-of-stack
 14 	Stack() {
 15 		tos = -1;
 16 	}
 17 
 18 	// Push an item onto the stack
 19 	void push(int item) {
 20 		if (tos == 9)
 21 			System.out.println("Stack is full.");
 22 		else
 23 			stck[++tos] = item;
 24 	}
 25 
 26 	// Pop an item from the stack
 27 	int pop() {
 28 		if (tos < 0) {
 29 			System.out.println("Stack underflow.");
 30 			return 0;
 31 		} else
 32 			return stck[tos--];
 33 	}
 34 }
 35

View Code

  1 class TestStack {
  2   public static void main(String args[]) {
  3     Stack mystack1 = new Stack();
  4     Stack mystack2 = new Stack();
  5 
  6     // push some numbers onto the stack
  7     for(int i=0; i<10; i++) mystack1.push(i);
  8     for(int i=10; i<20; i++) mystack2.push(i);
  9 
 10     // pop those numbers off the stack
 11     System.out.println("Stack in mystack1:");
 12     for(int i=0; i<10; i++)
 13        System.out.println(mystack1.pop());
 14 
 15     System.out.println("Stack in mystack2:");
 16     for(int i=0; i<10; i++)
 17        System.out.println(mystack2.pop());
 18 
 19     // these statements are not legal
 20     // mystack1.tos = -2;
 21     // mystack2.stck[3] = 100; 
 22   }
 23 }

View Code

7.7 理解st

  1 // Demonstrate static variables, methods, and blocks.
  2 class UseStatic {
  3   static int a = 3;
  4   static int b;
  5 
  6   static void meth(int x) {
  7     System.out.println("x = " + x);
  8     System.out.println("a = " + a);
  9     System.out.println("b = " + b);
 10   }
 11 
 12   static {
 13     System.out.println("Static block initialized.");
 14     b = a * 4;
 15   }
 16 
 17   public static void main(String args[]) {
 18     meth(42);
 19   }
 20 }

View Code

  1 class StaticDemo {
  2   static int a = 42;
  3   static int b = 99;
  4   static void callme() {
  5     System.out.println("a = " + a);
  6   }
  7 }
  8 
  9 class StaticByName {
 10   public static void main(String args[]) {
 11     StaticDemo.callme();
 12     System.out.println("b = " + StaticDemo.b);
 13   }
 14 }
 15

View Code

7.8 final介绍

7.9 重新审视数组

  1 // This program demonstrates the length array member.
  2 class Length {
  3   public static void main(String args[]) {
  4     int a1[] = new int[10];
  5     int a2[] = {3, 5, 7, 1, 8, 99, 44, -10};
  6     int a3[] = {4, 3, 2, 1};
  7 
  8     System.out.println("length of a1 is " + a1.length);
  9     System.out.println("length of a2 is " + a2.length);
 10     System.out.println("length of a3 is " + a3.length);
 11   }
 12 }
 13

View Code

  1 // Improved Stack class that uses the length array member.
  2 class Stack {
  3   private int stck[];
  4   private int tos;
  5 
  6   // allocate and initialize stack
  7   Stack(int size) {
  8     stck = new int[size];
  9     tos = -1;
 10   }
 11 
 12   // Push an item onto the stack
 13   void push(int item) {
 14     if(tos==stck.length-1) // use length member 
 15       System.out.println("Stack is full.");
 16     else
 17       stck[++tos] = item;
 18   }
 19 
 20   // Pop an item from the stack
 21   int pop() {
 22     if(tos < 0) {
 23       System.out.println("Stack underflow.");
 24       return 0;
 25     }
 26     else
 27       return stck[tos--];
 28   }
 29 }

View Code

  1 class TestStack2 {
  2   public static void main(String args[]) {
  3     Stack mystack1 = new Stack(5);
  4     Stack mystack2 = new Stack(8);
  5 
  6     // push some numbers onto the stack
  7     for(int i=0; i<5; i++) mystack1.push(i);
  8     for(int i=0; i<8; i++) mystack2.push(i);
  9 
 10     // pop those numbers off the stack
 11     System.out.println("Stack in mystack1:");
 12     for(int i=0; i<5; i++)
 13        System.out.println(mystack1.pop());
 14 
 15     System.out.println("Stack in mystack2:");
 16     for(int i=0; i<8; i++)
 17        System.out.println(mystack2.pop());
 18   }
 19 }

View Code

7.10 嵌套类和内部类

  1 // Demonstrate an inner class.
  2 class Outer {
  3   int outer_x = 100;
  4 
  5   void test() {
  6     Inner inner = new Inner();
  7     inner.display();
  8   }
  9 
 10   // this is an innner class
 11   class Inner {
 12     void display() {
 13       System.out.println("display: outer_x = " + outer_x);
 14     }
 15   }
 16 }
 17 
 18 class InnerClassDemo {
 19   public static void main(String args[]) {
 20     Outer outer = new Outer();
 21     outer.test();
 22   }
 23 }
 24

View Code

  1 // This program will not compile.
  2 class Outer {
  3   int outer_x = 100;
  4 
  5   void test() {
  6     Inner inner = new Inner();
  7     inner.display();
  8   }
  9 
 10   // this is an innner class
 11   class Inner {
 12     int y = 10; // y is local to Inner
 13     void display() {
 14       System.out.println("display: outer_x = " + outer_x);
 15     }
 16   }
 17 
 18   void showy() {
 19     System.out.println(y); // error, y not known here!
 20   }
 21 }
 22 
 23 class InnerClassDemo {
 24   public static void main(String args[]) {
 25     Outer outer = new Outer();
 26     outer.test();
 27   }
 28 }
 29

View Code

  1 
  2 // Define an inner class within a for loop.
  3 class Outer {
  4   int outer_x = 100;
  5 
  6   void test() {
  7     for(int i=0; i<10; i++) {
  8       class Inner {
  9         void display() {
 10           System.out.println("display: outer_x = " + outer_x);
 11         }
 12       }
 13       Inner inner = new Inner();
 14       inner.display();
 15     }
 16   }
 17 }
 18 
 19 class InnerClassDemo {
 20   public static void main(String args[]) {
 21     Outer outer = new Outer();
 22     outer.test();
 23   }
 24 }
 25

7.11 String类介绍

  1 // Demonstrating Strings.
  2 class StringDemo {
  3   public static void main(String args[]) {
  4     String strOb1 = "First String";
  5     String strOb2 = "Second String";
  6     String strOb3 = strOb1 + " and " + strOb2;
  7 
  8     System.out.println(strOb1);
  9     System.out.println(strOb2);
 10     System.out.println(strOb3);
 11   }
 12 }

  1 // Demonstrating some String methods.
  2 class StringDemo2 {
  3   public static void main(String args[]) {
  4     String strOb1 = "First String";
  5     String strOb2 = "Second String";
  6     String strOb3 = strOb1;
  7 
  8     System.out.println("Length of strOb1: " +    strOb1.length());
  9 
 10     System.out.println("Char at index 3 in strOb1: " + strOb1.charAt(3));
 11 
 12     if(strOb1.equals(strOb2)) {
 13       System.out.println("strOb1 == strOb2");
 14     }else{
 15       System.out.println("strOb1 != strOb2");
 16     }
 17 
 18     if(strOb1.equals(strOb3)) {
 19       System.out.println("strOb1 == strOb3");}
 20     else{
 21       System.out.println("strOb1 != strOb3");}
 22   }
 23 }
 24

  1 // Demonstrate String arrays.
  2 class StringDemo3 {
  3   public static void main(String args[]) {
  4     String str[] = { "one", "two", "three" };
  5 
  6     for(int i=0; i<str.length; i++)
  7       System.out.println("str[" + i + "]: " + str[i]);
  8   }
  9 }
 10

7.12 使用命令行参数

  1 class CommandLine {
  2   public static void main(String args[]) {
  3     for(int i=0; i<args.length; i++)
  4       System.out.println("args[" + i + "]: " +   args[i]);
  5   }
  6 }
  7

7.13 varargs：可变长度参数

  1 // Use an array to pass a variable number of 
  2 // arguments to a method. 
  3 class PassArray {
  4   static void vaTest(int v[]) {
  5     System.out.print("Number of args: " + v.length +  " Contents: ");
  6 
  7     for(int x : v){
  8       System.out.print(x + " ");
  9     }
 10     System.out.println();
 11   }
 12 
 13   public static void main(String args[])
 14   {
 15     // Notice how an array must be created to 
 16     // hold the arguments. 
 17     int n1[] = { 10 };
 18     int n2[] = { 1, 2, 3 };
 19     int n3[] = { };
 20 
 21     vaTest(n1); // 1 arg 
 22     vaTest(n2); // 3 args 
 23     vaTest(n3); // no args 
 24   }
 25 }

  1 // Demonstrate variable-length arguments. 
  2 class VarArgs {
  3 
  4   // vaTest() now uses a vararg. 
  5   static void vaTest(int ... v) {
  6     System.out.print("Number of args: " + v.length +  " Contents: ");
  7 
  8     for(int x : v) {
  9       System.out.print(x + " ");
 10     }
 11     System.out.println();
 12   }
 13 
 14   public static void main(String args[])
 15   {
 16 
 17     // Notice how vaTest() can be called with a 
 18     // variable number of arguments. 
 19     vaTest(10);      // 1 arg 
 20     vaTest(1, 2, 3); // 3 args 
 21     vaTest();        // no args 
 22   }
 23 }
 24

  1 // Use varargs with standard arguments. 
  2 class VarArgs2 {
  3 
  4   // Here, msg is a normal parameter and v is a 
  5   // varargs parameter. 
  6   static void vaTest(String msg, int ... v) {
  7     System.out.print(msg + v.length +
  8                         " Contents: ");
  9 
 10     for(int x : v) {
 11       System.out.print(x + " ");
 12      }
 13 
 14     System.out.println();
 15   }
 16 
 17   public static void main(String args[])
 18   {
 19     vaTest("One vararg: ", 10);
 20     vaTest("Three varargs: ", 1, 2, 3);
 21     vaTest("No varargs: ");
 22   }
 23 }
 24

7.13.1 重载varargs方法

  1 // Varargs and overloading. 
  2 class VarArgs3 {
  3 
  4   static void vaTest(int ... v) {
  5     System.out.print("vaTest(int ...): " +  "Number of args: " + v.length +  " Contents: ");
  6 
  7     for(int x : v) {
  8       System.out.print(x + " ");
  9     }
 10     System.out.println();
 11   }
 12 
 13   static void vaTest(boolean ... v) {
 14     System.out.print("vaTest(boolean ...) " +  "Number of args: " + v.length +  " Contents: ");
 15 
 16     for(boolean x : v) {
 17       System.out.print(x + " ");
 18     }
 19     System.out.println();
 20   }
 21 
 22   static void vaTest(String msg, int ... v) {
 23     System.out.print("vaTest(String, int ...): " +  msg + v.length +  " Contents: ");
 24 
 25     for(int x : v) {
 26       System.out.print(x + " ");
 27      }
 28     System.out.println();
 29   }
 30 
 31   public static void main(String args[])
 32   {
 33     vaTest(1, 2, 3);
 34     vaTest("Testing: ", 10, 20);
 35     vaTest(true, false, false);
 36

7.13.2 varargs方法与模糊性

  1 // Varargs, overloading, and ambiguity. 
  2 // 
  3 // This program contains an error and will 
  4 // not compile! 
  5 class VarArgs4 {
  6 
  7   static void vaTest(int ... v) {
  8     System.out.print("vaTest(Integer ...): " +  "Number of args: " + v.length +  " Contents: ");
  9 
 10     for(int x : v) {
 11       System.out.print(x + " ");
 12     }
 13     System.out.println();
 14   }
 15 
 16   static void vaTest(boolean ... v) {
 17     System.out.print("vaTest(boolean ...) " +  "Number of args: " + v.length +  " Contents: ");
 18 
 19     for(boolean x : v) {
 20       System.out.print(x + " ");
 21    }
 22     System.out.println();
 23   }
 24 
 25 
 26   public static void main(String args[])
 27   {
 28     vaTest(1, 2, 3);  // OK 
 29     vaTest(true, false, false); // OK 
 30 
 31     vaTest(); // Error: Ambiguous! 
 32   }
 33 }

第8章继承

8.1 继承的基础知识

  1 // A simple example of inheritance.
  2 
  3 // Create a superclass.
  4 class A {
  5   int i, j;
  6 
  7   void showij() {
  8     System.out.println("i and j: " + i + " " + j);
  9   }
 10 }
 11 
 12 // Create a subclass by extending class A.
 13 class B extends A {
 14   int k;
 15 
 16   void showk() {
 17     System.out.println("k: " + k);
 18   }
 19   void sum() {
 20     System.out.println("i+j+k: " + (i+j+k));
 21   }
 22 }
 23 
 24 class SimpleInheritance {
 25   public static void main(String args[]) {
 26     A superOb = new A();
 27     B subOb = new B();
 28 
 29     // The superclass may be used by itself.
 30     superOb.i = 10;
 31     superOb.j = 20;
 32     System.out.println("Contents of superOb: ");
 33     superOb.showij();
 34     System.out.println();
 35 
 36     /* The subclass has access to all public members of
 37        its superclass. */
 38     subOb.i = 7;
 39     subOb.j = 8;
 40     subOb.k = 9;
 41     System.out.println("Contents of subOb: ");
 42     subOb.showij();
 43     subOb.showk();
 44     System.out.println();
 45 
 46     System.out.println("Sum of i, j and k in subOb:");
 47     subOb.sum();
 48   }
 49 }
 50

8.1.1 成员访问与继承

  1 /* In a class hierarchy, private members remain
  2    private to their class.
  3 
  4    This program contains an error and will not
  5    compile.
  6 */
  7 
  8 // Create a superclass.
  9 class A {
 10   int i; // public be default
 11   private int j; // private to A
 12 
 13   void setij(int x, int y) {
 14     i = x;
 15     j = y;
 16   }
 17 }
 18 
 19 // A's j is not accessible here.
 20 class B extends A {
 21   int total;
 22 
 23   void sum() {
 24     total = i + j; // ERROR, j is not accessible here
 25   }
 26 }
 27 
 28 class Access {
 29   public static void main(String args[]) {
 30     B subOb = new B();
 31 
 32     subOb.setij(10, 12);
 33 
 34     subOb.sum();
 35     System.out.println("Total is " + subOb.total);
 36   }
 37 }
 38

8.1.2 一个更实际的例子

  1 // This program uses inheritance to extend Box.
  2 class Box {
  3   double width;
  4   double height;
  5   double depth;
  6 
  7   // construct clone of an object
  8   Box(Box ob) { // pass object to constructor
  9     width = ob.width;
 10     height = ob.height;
 11     depth = ob.depth;
 12   }
 13 
 14   // constructor used when all dimensions specified
 15   Box(double w, double h, double d) {
 16     width = w;
 17     height = h;
 18     depth = d;
 19   }
 20 
 21   // constructor used when no dimensions specified
 22   Box() {
 23     width = -1;  // use -1 to indicate
 24     height = -1; // an uninitialized
 25     depth = -1;  // box
 26   }
 27 
 28   // constructor used when cube is created
 29   Box(double len) {
 30     width = height = depth = len;
 31   }
 32 
 33   // compute and return volume
 34   double volume() {
 35     return width * height * depth;
 36   }
 37 }
 38 
 39 // Here, Box is extened to include weight.
 40 class BoxWeight extends Box {
 41   double weight; // weight of box
 42 
 43   // constructor for BoxWeight
 44   BoxWeight(double w, double h, double d, double m) {
 45     width = w;
 46     height = h;
 47     depth = d;
 48     weight = m;
 49   }
 50 }
 51 
 52 class DemoBoxWeight {
 53   public static void main(String args[]) {
 54     BoxWeight mybox1 = new BoxWeight(10, 20, 15, 34.3);
 55     BoxWeight mybox2 = new BoxWeight(2, 3, 4, 0.076);
 56     double vol;
 57 
 58     vol = mybox1.volume();
 59     System.out.println("Volume of mybox1 is " + vol);
 60     System.out.println("Weight of mybox1 is " + mybox1.weight);
 61     System.out.println();
 62 
 63     vol = mybox2.volume();
 64     System.out.println("Volume of mybox2 is " + vol);
 65     System.out.println("Weight of mybox2 is " + mybox2.weight);
 66   }
 67 }
 68

  1 // Here, Box is extended to include color.
  2 class ColorBox extends Box {
  3   int color; // color of box
  4 
  5   ColorBox(double w, double h, double d, int c) {
  6     width = w;
  7     height = h;
  8     depth = d;
  9     color = c;
 10   }
 11 }
 12

8.1.3 超类变量可以引用子类对象

  1 class RefDemo {
  2   public static void main(String args[]) {
  3     BoxWeight weightbox = new BoxWeight(3, 5, 7, 8.37);
  4     Box plainbox = new Box();
  5     double vol;
  6 
  7     vol = weightbox.volume();
  8     System.out.println("Volume of weightbox is " + vol);
  9     System.out.println("Weight of weightbox is " + weightbox.weight);
 10     System.out.println();
 11 
 12     // assign BoxWeight reference to Box reference
 13     plainbox = weightbox;
 14 
 15     vol = plainbox.volume(); // OK, volume() defined in Box
 16     System.out.println("Volume of plainbox is " + vol);
 17 
 18     /* The following statement is invalid because plainbox
 19        does not define a weight member. */
 20 //  System.out.println("Weight of plainbox is " + plainbox.weight);
 21   }
 22 }

8.2 使用super关键字

8.2.1 使用super调用超类的构造函数

  1 // BoxWeight now uses super to initialize its Box attributes.
  2 class BoxWeight extends Box {
  3   double weight; // weight of box
  4 
  5   // initialize width, height, and depth using super()
  6   BoxWeight(double w, double h, double d, double m) {
  7     super(w, h, d); // call superclass constructor
  8     weight = m;
  9   }
 10 }

  1  // A complete implementation of BoxWeight.
  2 class Box {
  3   private double width;
  4   private double height;
  5   private double depth;
  6 
  7   // construct clone of an object
  8   Box(Box ob) { // pass object to constructor
  9     width double h, double d) {
 10     width = w;
 11     height = h;
 12     depth = d;
 13   }
 14 
 15   // constructor used when no dimensions specified
 16   Box() {
 17     width = -1;  // use -1 to indicate
 18     height = -1; // an uninitialized
 19     depth = -1;  // box
 20   }
 21  = ob.width;
 22     height = ob.height;
 23     depth = ob.depth;
 24   }
 25 
 26   // constructor used when all dimensions specified
 27   Box(double w,
 28   // constructor used when cube is created
 29   Box(double len) {
 30     width = height = depth = len;
 31   }
 32 
 33   // compute and return volume
 34   double volume() {
 35     return width * height * depth;
 36   }
 37 }
 38 
 39 // BoxWeight now fully implements all constructors.
 40 class BoxWeight extends Box {
 41   double weight; // weight of box
 42 
 43   // construct clone of an object
 44   BoxWeight(BoxWeight ob) { // pass object to constructor
 45     super(ob);
 46     weight = ob.weight;
 47   }
 48 
 49   // constructor when all parameters are specified
 50   BoxWeight(double w, double h, double d, double m) {
 51     super(w, h, d); // call superclass constructor
 52     weight = m;
 53   }
 54 
 55   // default constructor
 56   BoxWeight() {
 57     super();
 58     weight = -1;
 59   }
 60 
 61   // constructor used when cube is created
 62   BoxWeight(double len, double m) {
 63     super(len);
 64     weight = m;
 65   }
 66 }
 67 
 68 class DemoSuper {
 69   public static void main(String args[]) {
 70     BoxWeight mybox1 = new BoxWeight(10, 20, 15, 34.3);
 71     BoxWeight mybox2 = new BoxWeight(2, 3, 4, 0.076);
 72     BoxWeight mybox3 = new BoxWeight(); // default
 73     BoxWeight mycube = new BoxWeight(3, 2);
 74     BoxWeight myclone = new BoxWeight(mybox1);
 75     double vol;
 76 
 77     vol = mybox1.volume();
 78     System.out.println("Volume of mybox1 is " + vol);
 79     System.out.println("Weight of mybox1 is " + mybox1.weight);
 80     System.out.println();
 81 
 82     vol = mybox2.volume();
 83     System.out.println("Volume of mybox2 is " + vol);
 84     System.out.println("Weight of mybox2 is " + mybox2.weight);
 85     System.out.println();
 86 
 87     vol = mybox3.volume();
 88     System.out.println("Volume of mybox3 is " + vol);
 89     System.out.println("Weight of mybox3 is " + mybox3.weight);
 90     System.out.println();
 91 
 92     vol = myclone.volume();
 93     System.out.println("Volume of myclone is " + vol);
 94     System.out.println("Weight of myclone is " + myclone.weight);
 95     System.out.println();
 96 
 97     vol = mycube.volume();
 98     System.out.println("Volume of mycube is " + vol);
 99     System.out.println("Weight of mycube is " + mycube.weight);
100     System.out.println();
101   }
102 }
103

  1 // construct clone of an object
  2 BoxWeight(BoxWeight ob) { // pass object to constructor
  3   super(ob);
  4   weight = ob.weight;
  5 }
  6

8.2.2 super的另一种用法

  1 // Using super to overcome name hiding.
  2 class A {
  3   int i;
  4 }
  5 
  6 // Create a subclass by extending class A.
  7 class B extends A {
  8   int i; // this i hides the i in A
  9 
 10   B(int a, int b) {
 11     super.i = a; // i in A
 12     i = b; // i in B
 13   }
 14 
 15   void show() {
 16     System.out.println("i in superclass: " + super.i);
 17     System.out.println("i in subclass: " + i);
 18   }
 19 }
 20 
 21 class UseSuper {
 22   public static void main(String args[]) {
 23     B subOb = new B(1, 2);
 24 
 25     subOb.show();
 26   }
 27 }
 28

8.3 创建多级继承层次

  1 // Extend BoxWeight to include shipping costs.
  2 
  3 // Start with Box.
  4 class Box {
  5   private double width;
  6   private double height;
  7   private double depth;
  8 
  9   // construct clone of an object
 10   Box(Box ob) { // pass object to constructor
 11     width = ob.width;
 12     height = ob.height;
 13     depth = ob.depth;
 14   }
 15 
 16   // constructor used when all dimensions specified
 17   Box(double w, double h, double d) {
 18     width = w;
 19     height = h;
 20     depth = d;
 21   }
 22 
 23   // constructor used when no dimensions specified
 24   Box() {
 25     width = -1;  // use -1 to indicate
 26     height = -1; // an uninitialized
 27     depth = -1;  // box
 28   }
 29 
 30   // constructor used when cube is created
 31   Box(double len) {
 32     width = height = depth = len;
 33   }
 34 
 35   // compute and return volume
 36   double volume() {
 37     return width * height * depth;
 38   }
 39 }
 40 
 41 // Add weight.
 42 class BoxWeight extends Box {
 43   double weight; // weight of box
 44 
 45   // construct clone of an object
 46   BoxWeight(BoxWeight ob) { // pass object to constructor
 47     super(ob);
 48     weight = ob.weight;
 49   }
 50 
 51   // constructor when all parameters are specified
 52   BoxWeight(double w, double h, double d, double m) {
 53     super(w, h, d); // call superclass constructor
 54     weight = m;
 55   }
 56 
 57   // default constructor
 58   BoxWeight() {
 59     super();
 60     weight = -1;
 61   }
 62 
 63   // constructor used when cube is created
 64   BoxWeight(double len, double m) {
 65     super(len);
 66     weight = m;
 67   }
 68 }
 69 
 70 // Add shipping costs
 71 class Shipment extends BoxWeight {
 72   double cost;
 73 
 74   // construct clone of an object
 75   Shipment(Shipment ob) { // pass object to constructor
 76     super(ob);
 77     cost = ob.cost;
 78   }
 79 
 80   // constructor when all parameters are specified
 81   Shipment(double w, double h, double d,
 82             double m, double c) {
 83     super(w, h, d, m); // call superclass constructor
 84     cost = c;
 85   }
 86 
 87   // default constructor
 88   Shipment() {
 89     super();
 90     cost = -1;
 91   }
 92 
 93   // constructor used when cube is created
 94   Shipment(double len, double m, double c) {
 95     super(len, m);
 96     cost = c;
 97   }
 98 }
 99 
100 class DemoShipment {
101   public static void main(String args[]) {
102     Shipment shipment1 =
103                new Shipment(10, 20, 15, 10, 3.41);
104     Shipment shipment2 =
105                new Shipment(2, 3, 4, 0.76, 1.28);
106 
107     double vol;
108 
109     vol = shipment1.volume();
110     System.out.println("Volume of shipment1 is " + vol);
111     System.out.println("Weight of shipment1 is "
112

8.4 构造函数的调用时机

  1 // Demonstrate when constructors are called.
  2 
  3 // Create a super class.
  4 class A {
  5   A() {
  6     System.out.println("Inside A's constructor.");
  7   }
  8 }
  9 
 10 // Create a subclass by extending class A.
 11 class B extends A {
 12   B() {
 13     System.out.println("Inside B's constructor.");
 14   }
 15 }
 16 
 17 // Create another subclass by extending B.
 18 class C extends B {
 19   C() {
 20     System.out.println("Inside C's constructor.");
 21   }
 22 }
 23 
 24 class CallingCons {
 25   public static void main(String args[]) {
 26     C c = new C();
 27   }
 28 }
 29

8.5 方法重写

  1 // Method overriding.
  2 class A {
  3   int i, j;
  4 
  5   A(int a, int b) {
  6     i = a;
  7     j = b;
  8   }
  9 
 10   // display i and j
 11   void show() {
 12     System.out.println("i and j: " + i + " " + j);
 13   }
 14 }
 15 
 16 class B extends A {
 17   int k;
 18 
 19   B(int a, int b, int c) {
 20     super(a, b);
 21     k = c;
 22   }
 23 
 24   // display k -- this overrides show() in A
 25   void show() {
 26     System.out.println("k: " + k);
 27   }
 28 }
 29 
 30 class Override {
 31   public static void main(String args[]) {
 32     B subOb = new B(1, 2, 3);
 33 
 34     subOb.show(); // this calls show() in B
 35   }
 36 }
 37

  1 class B extends A {
  2   int k;
  3 
  4   B(int a, int b, int c) {
  5     super(a, b);
  6     k = c;
  7   }
  8 
  9   void show() {
 10     super.show(); // this calls A's show()
 11     System.out.println("k: " + k);
 12   }
 13 }
 14

  1 // Methods with differing type signatures are overloaded -- not overridden.
  2 class A {
  3   int i, j;
  4 
  5   A(int a, int b) {
  6     i = a;
  7     j = b;
  8   }
  9 
 10   // display i and j
 11   void show() {
 12     System.out.println("i and j: " + i + " " + j);
 13   }
 14 }
 15 
 16 // Create a subclass by extending class A.
 17 class B extends A {
 18   int k;
 19 
 20   B(int a, int b, int c) {
 21     super(a, b);
 22     k = c;
 23   }
 24 
 25   // overload show()
 26   void show(String msg) {
 27     System.out.println(msg + k);
 28   }
 29 }
 30 
 31 class Override {
 32   public static void main(String args[]) {
 33     B subOb = new B(1, 2, 3);
 34 
 35     subOb.show("This is k: "); // this calls show() in B
 36     subOb.show(); // this calls show() in A
 37   }
 38 }
 39

8.6 动态方法调度

  1 // Dynamic Method Dispatch
  2 class A {
  3    void callme() {
  4      System.out.println("Inside A's callme method");
  5   }
  6 }
  7 
  8 class B extends A {
  9   // override callme()
 10   void callme() {
 11     System.out.println("Inside B's callme method");
 12   }
 13 }
 14 
 15 class C extends A {
 16   // override callme()
 17   void callme() {
 18     System.out.println("Inside C's callme method");
 19   }
 20 }
 21 
 22 class Dispatch {
 23   public static void main(String args[]) {
 24     A a = new A(); // object of type A
 25     B b = new B(); // object of type B
 26     C c = new C(); // object of type C
 27     A r; // obtain a reference of type A    
 28 
 29     r = a; // r refers to an A object
 30     r.callme(); // calls A's version of callme
 31 
 32     r = b; // r refers to a B object
 33     r.callme(); // calls B's version of callme
 34 
 35     r = c; // r refers to a C object
 36     r.callme(); // calls C's version of callme
 37   }
 38 }
 39

8.6.1 重写方法的目的

8.6.2 应用方法重写

  1 // Using run-time polymorphism.
  2 class Figure {
  3   double dim1;
  4   double dim2;
  5 
  6   Figure(double a, double b) {
  7     dim1 = a;
  8     dim2 = b;
  9   }
 10 
 11   double area() {
 12     System.out.println("Area for Figure is undefined.");
 13     return 0;
 14   }
 15 }
 16 
 17 class Rectangle extends Figure {
 18   Rectangle(double a, double b) {
 19     super(a, b);
 20   }
 21 
 22   // override area for rectangle
 23   double area() {
 24     System.out.println("Inside Area for Rectangle.");
 25     return dim1 * dim2;
 26   }
 27 }
 28 
 29 class Triangle extends Figure {
 30   Triangle(double a, double b) {
 31     super(a, b);
 32   }
 33 
 34   // override area for right triangle
 35   double area() {
 36     System.out.println("Inside Area for Triangle.");
 37     return dim1 * dim2 / 2;
 38   }
 39 }
 40 
 41 class FindAreas {
 42   public static void main(String args[]) {
 43     Figure f = new Figure(10, 10);
 44     Rectangle r = new Rectangle(9, 5);
 45     Triangle t = new Triangle(10, 8);
 46 
 47     Figure figref;
 48 
 49     figref = r;
 50     System.out.println("Area is " + figref.area());
 51 
 52     figref = t;
 53     System.out.println("Area is " + figref.area());
 54 
 55     figref = f;
 56     System.out.println("Area is " + figref.area());
 57   }
 58 }
 59

8.7 使用抽象类

  1 // A Simple demonstration of abstract.
  2 abstract class A {
  3   abstract void callme();
  4 
  5   // concrete methods are still allowed in abstract classes
  6   void callmetoo() {
  7     System.out.println("This is a concrete method.");
  8   }
  9 }
 10 
 11 class B extends A {
 12   void callme() {
 13     System.out.println("B's implementation of callme.");
 14   }
 15 }
 16 
 17 class AbstractDemo {
 18   public static void main(String args[]) {
 19     B b = new B();
 20 
 21     b.callme();
 22     b.callmetoo();
 23   }
 24 }

  1 // Using abstract methods and classes.
  2 abstract class Figure {
  3   double dim1;
  4   double dim2;
  5 
  6   Figure(double a, double b) {
  7     dim1 = a;
  8     dim2 = b;
  9   }
 10 
 11   // area is now an an abstract method 
 12   abstract double area();
 13 }
 14 
 15 class Rectangle extends Figure {
 16   Rectangle(double a, double b) {
 17     super(a, b);
 18   }
 19 
 20   // override area for rectangle
 21   double area() {
 22     System.out.println("Inside Area for Rectangle.");
 23     return dim1 * dim2;
 24   }
 25 }
 26 
 27 class Triangle extends Figure {
 28   Triangle(double a, double b) {
 29     super(a, b);
 30   }
 31 
 32   // override area for right triangle
 33   double area() {
 34     System.out.println("Inside Area for Triangle.");
 35     return dim1 * dim2 / 2;
 36   }
 37 }
 38 
 39 class AbstractAreas {
 40   public static void main(String args[]) {
 41   // Figure f = new Figure(10, 10); // illegal now
 42     Rectangle r = new Rectangle(9, 5);
 43     Triangle t = new Triangle(10, 8);
 44 
 45     Figure figref; // this is OK, no object is created
 46 
 47     figref = r;
 48     System.out.println("Area is " + figref.area());
 49 
 50     figref = t;
 51     System.out.println("Area is " + figref.area());
 52   }
 53 }

8.8 在继承中使用final关键字

8.8.1 使用final关键字阻止重写

  1 class A {
  2   final void meth() {
  3     System.out.println("This is a final method.");
  4   }
  5 }
  6 
  7 class B extends A {
  8   void meth() { // ERROR! Can't override.
  9     System.out.println("Illegal!");
 10   }
 11 }
 12

8.8.2 使用final关键字阻止继承

  1 final class A {
  2   // ...
  3 }
  4 
  5 // The following class is illegal.
  6 class B extends A { // ERROR! Can't subclass A
  7   // ...
  8 }

8.9 Object类

第9章包和接口

9.1 包

9.1.1 定义包

9.1.2 包查找与CLASSPATH

9.1.3 一个简短的包示例

  1 // A simple package
  2 package MyPack;
  3 
  4 class Balance {
  5   String name;
  6   double bal;
  7 
  8   Balance(String n, double b) {
  9     name = n;
 10     bal = b;
 11   }
 12 
 13   void show() {
 14     if(bal<0)
 15       System.out.print("-->> ");
 16     System.out.println(name + ": $" + bal);
 17   }
 18 }
 19 
 20 class AccountBalance {
 21   public static void main(String args[]) {
 22     Balance current[] = new Balance[3];
 23 
 24     current[0] = new Balance("K. J. Fielding", 123.23);
 25     current[1] = new Balance("Will Tell", 157.02);
 26     current[2] = new Balance("Tom Jackson", -12.33);
 27 
 28     for(int i=0; i<3; i++) current[i].show();
 29   }
 30 }

9.2 访问保护

  1 package p1;
  2 
  3 public class Protection {
  4   int n = 1;
  5   private int n_pri = 2;
  6   protected int n_pro = 3;
  7   public int n_pub = 4;
  8 
  9   public Protection() {
 10     System.out.println("base constructor");
 11     System.out.println("n = " + n);
 12     System.out.println("n_pri = " + n_pri);
 13     System.out.println("n_pro = " + n_pro);
 14     System.out.println("n_pub = " + n_pub);
 15   }
 16 }
 17 
 18 class Derived extends Protection {
 19   Derived() {
 20     System.out.println("derived constructor");
 21     System.out.println("n = " + n);
 22 
 23 //  class only
 24 //  System.out.println("n_pri = " + n_pri);
 25 
 26     System.out.println("n_pro = " + n_pro);
 27     System.out.println("n_pub = " + n_pub);
 28   }
 29 }
 30 
 31 class SamePackage {
 32   SamePackage() {
 33     Protection p = new Protection();
 34     System.out.println("same package constructor");
 35     System.out.println("n = " + p.n);
 36 
 37 //  class only
 38 //  System.out.println("n_pri = " + p.n_pri);
 39 
 40     System.out.println("n_pro = " + p.n_pro);
 41     System.out.println("n_pub = " + p.n_pub);
 42   }
 43 }
 44

  1 package p2;
  2 
  3 class Protection2 extends p1.Protection {
  4   Protection2() {
  5     System.out.println("derived other package constructor");
  6 
  7 //  class or package only
  8 //  System.out.println("n = " + n);
  9 
 10 //  class only
 11 //  System.out.println("n_pri = " + n_pri);
 12 
 13     System.out.println("n_pro = " + n_pro);
 14     System.out.println("n_pub = " + n_pub);
 15   }
 16 }
 17 
 18 class OtherPackage {
 19   OtherPackage() {
 20     p1.Protection p = new p1.Protection();
 21     System.out.println("other package constructor");
 22 
 23 //  class or package only
 24 //  System.out.println("n = " + p.n);
 25 
 26 //  class only
 27 //  System.out.println("n_pri = " + p.n_pri);
 28 
 29 //  class, subclass or package only
 30 //  System.out.println("n_pro = " + p.n_pro);
 31 
 32     System.out.println("n_pub = " + p.n_pub);
 33   }
 34 }

  1 // Demo package p1.
  2 package p1;
  3 
  4 // Instantiate the various classes in p1.
  5 public class Demo {
  6   public static void main(String args[]) {
  7     Protection ob1 = new Protection();
  8     Derived ob2 = new Derived();
  9     SamePackage ob3 = new SamePackage();
 10   }
 11 }
 12

  1 // Demo package p2.
  2 package p2;
  3 
  4 // Instantiate the various classes in p2.
  5 public class Demo {
  6   public static void main(String args[]) {
  7     Protection2 ob1 = new Protection2();
  8     OtherPackage ob2 = new OtherPackage();
  9   }
 10 }
 11

9.3 导入包

  1 package JavaBase_ReferenceNanual.Chap9.listing8.MyPack;
  2 
  3 /**
  4  * 项目名称：JavaEE_Base
  5  * 类名称：Balance
  6  * 类描述： Now, the Balance class, its constructor,
  7  * and its show() method are public. This means that they can be used by
  8  * non-subclass code outside their package.
  9  * 创建人： shall_liu(1136808529@qq.com)
 10  * 创建时间：2017年9月21日 上午12:01:36
 11  * 修改人：amin
 12  * 修改时间：2017年9月21日 上午12:01:36
 13  * 修改备注：
 14  * @version
 15  */
 16 public class Balance {
 17 	String name;
 18 	double bal;
 19 
 20 	public Balance(String n, double b) {
 21 		name = n;
 22 		bal = b;
 23 	}
 24 
 25 	public void show() {
 26 		if (bal < 0)
 27 			System.out.print("-->> ");
 28 		System.out.println(name + ": $" + bal);
 29 	}
 30 }

  1 package JavaBase_ReferenceNanual.Chap9.listing9.MyPack;
  2 
  3 import JavaBase_ReferenceNanual.Chap9.listing8.MyPack.*;
  4 /**
  5  *
  6 *
  7 * 项目名称：JavaEE_Base
  8 * 类名称：TestBalance
  9 * 类描述：
 10 * 创建人：  shall_liu(1136808529@qq.com)
 11 * 创建时间：2017年9月21日 上午12:06:30
 12 * 修改人：amin
 13 * 修改时间：2017年9月21日 上午12:06:30
 14 * 修改备注：
 15 * @version
 16 *
 17  */
 18 class TestBalance {
 19   public static void main(String args[]) {
 20 
 21     /* Because Balance is public, you may use Balance
 22        class and call its constructor. */
 23     Balance test = new Balance("J. J. Jaspers", 99.88);
 24 
 25     test.show(); // you may also call show()
 26   }
 27 }
 28

9.4 接口

9.4.1 定义接口

9.4.2 实现接口

  1 package JavaBase_ReferenceNanual.Chap9.listing9.MyPack;
  2 
  3 import javax.security.auth.callback.Callback;
  4 
  5 class Client implements Callback {
  6 	// Implement Callback's interface
  7 	public void callback(int p) {
  8 		System.out.println("callback called with " + p);
  9 	}
 10 
 11 	void nonIfaceMeth() {
 12 		System.out.println("Classes that implement interfaces " + "may also define other members, too.");
 13 	}
 14 }
 15 
 16 package JavaBase_ReferenceNanual.Chap9.listing9.MyPack;
 17 
 18 import javax.security.auth.callback.Callback;
 19 /**
 20  *
 21 *
 22 * 项目名称：JavaEE_Base
 23 * 类名称：TestIface
 24 * 类描述：
 25 * 创建人：  shall_liu(1136808529@qq.com)
 26 * 创建时间：2017年9月21日 上午1:00:06
 27 * 修改人：amin
 28 * 修改时间：2017年9月21日 上午1:00:06
 29 * 修改备注：
 30 * @version
 31 *
 32  */
 33 class TestIface {
 34 	  public static void main(String args[]) {
 35 	    Callback c = new Client();
 36 	    ((Client) c).callback(42);
 37 	  }
 38 	}
 39 //运行结果为
 40 callback called with 42
 41

  1 package JavaBase_ReferenceNanual.Chap9.listing9.MyPack;
  2 
  3 import javax.security.auth.callback.Callback;
  4 
  5 /**
  6  *
  7 *
  8 * 项目名称：JavaEE_Base
  9 * 类名称：AnotherClient
 10 * 类描述：  Another implementation of Callback.
 11 * 创建人：  shall_liu(1136808529@qq.com)
 12 * 创建时间：2017年9月21日 上午1:03:26
 13 * 修改人：amin
 14 * 修改时间：2017年9月21日 上午1:03:26
 15 * 修改备注：
 16 * @version
 17 *
 18  */
 19 class AnotherClient implements Callback {
 20 	// Implement Callback's interface
 21 	public void callback(int p) {
 22 		System.out.println("Another version of callback");
 23 		System.out.println("p squared is " + (p * p));
 24 	}
 25 }
 26 
 27 
 28 package JavaBase_ReferenceNanual.Chap9.listing9.MyPack;
 29 
 30 import javax.security.auth.callback.Callback;
 31 
 32 class Client implements Callback {
 33 	// Implement Callback's interface
 34 	public void callback(int p) {
 35 		System.out.println("callback called with " + p);
 36 	}
 37 
 38 	void nonIfaceMeth() {
 39 		System.out.println("Classes that implement interfaces " + "may also define other members, too.");
 40 	}
 41 }
 42 
 43 package JavaBase_ReferenceNanual.Chap9.listing9.MyPack;
 44 
 45 import javax.security.auth.callback.Callback;
 46 
 47 /**
 48  *
 49 *
 50 * 项目名称：JavaEE_Base
 51 * 类名称：TestIface2
 52 * 类描述：
 53 * 创建人：  shall_liu(1136808529@qq.com)
 54 * 创建时间：2017年9月21日 上午1:04:49
 55 * 修改人：amin
 56 * 修改时间：2017年9月21日 上午1:04:49
 57 * 修改备注：
 58 * @version
 59 *
 60  */
 61 
 62 class TestIface2 {
 63 	public static void main(String args[]) {
 64 		Callback c = new Client();
 65 		AnotherClient ob = new AnotherClient();
 66 
 67 		((Client) c).callback(42);
 68 
 69 		c = ob; // c now refers to AnotherClient object
 70 		((Client) c).callback(42);
 71 	}
 72 }
 73

9.4.3 嵌套接口

  1 // A nested interface example.
  2 
  3 // This class contains a member interface.
  4 class A {
  5   // this is a nested interface
  6   public interface NestedIF {
  7     boolean isNotNegative(int x);
  8   }
  9 }
 10 
 11 // B implements the nested interface.
 12 class B implements A.NestedIF {
 13   public boolean isNotNegative(int x) {
 14     return x < 0 ? false : true;
 15   }
 16 }
 17 
 18 class NestedIFDemo {
 19   public static void main(String args[]) {
 20 
 21     // use a nested interface reference
 22     A.NestedIF nif = new B();
 23 
 24     if(nif.isNotNegative(10))
 25       System.out.println("10 is not negative");
 26     if(nif.isNotNegative(-12))
 27       System.out.println("this won't be displayed");
 28   }
 29 }
 30

9.4.4 应用接口

  1 // Define an integer stack interface.
  2 interface IntStack {
  3   void push(int item); // store an item
  4   int pop(); // retrieve an item
  5 }
  6 
  7 // An implementation of IntStack that uses fixed storage.
  8 class FixedStack implements IntStack {
  9   private int stck[];
 10   private int tos;
 11 
 12   // allocate and initialize stack
 13   FixedStack(int size) {
 14     stck = new int[size];
 15     tos = -1;
 16   }
 17 
 18   // Push an item onto the stack
 19   public void push(int item) {
 20     if(tos==stck.length-1) // use length member 
 21       System.out.println("Stack is full.");
 22     else
 23       stck[++tos] = item;
 24   }
 25 
 26   // Pop an item from the stack
 27   public int pop() {
 28     if(tos < 0) {
 29       System.out.println("Stack underflow.");
 30       return 0;
 31     }
 32     else
 33       return stck[tos--];
 34   }
 35 }
 36 
 37 class IFTest {
 38   public static void main(String args[]) {
 39     FixedStack mystack1 = new FixedStack(5);
 40     FixedStack mystack2 = new FixedStack(8);
 41 
 42     // push some numbers onto the stack
 43     for(int i=0; i<5; i++) mystack1.push(i);
 44     for(int i=0; i<8; i++) mystack2.push(i);
 45 
 46     // pop those numbers off the stack
 47     System.out.println("Stack in mystack1:");
 48     for(int i=0; i<5; i++)
 49        System.out.println(mystack1.pop());
 50 
 51     System.out.println("Stack in mystack2:");
 52     for(int i=0; i<8; i++)
 53        System.out.println(mystack2.pop());
 54   }
 55 }

  1 // Define an integer stack interface.
  2 interface IntStack {
  3   void push(int item); // store an item
  4   int pop(); // retrieve an item
  5 }
  6 
  7 // Implement a "growable" stack.
  8 class DynStack implements IntStack {
  9   private int stck[];
 10   private int tos;
 11 
 12   // allocate and initialize stack
 13   DynStack(int size) {
 14     stck = new int[size];
 15     tos = -1;
 16   }
 17 
 18   // Push an item onto the stack
 19   public void push(int item) {
 20     // if stack is full, allocate a larger stack
 21     if(tos==stck.length-1) {
 22       int temp[] = new int[stck.length * 2]; // double size
 23       for(int i=0; i<stck.length; i++) temp[i] = stck[i];
 24       stck = temp;
 25       stck[++tos] = item;
 26     }
 27     else
 28       stck[++tos] = item;
 29   }
 30 
 31   // Pop an item from the stack
 32   public int pop() {
 33     if(tos < 0) {
 34       System.out.println("Stack underflow.");
 35       return 0;
 36     }
 37     else
 38       return stck[tos--];
 39   }
 40 }
 41 
 42 class IFTest2 {
 43   public static void main(String args[]) {
 44     DynStack mystack1 = new DynStack(5);
 45     DynStack mystack2 = new DynStack(8);
 46 
 47     // these loops cause each stack to grow
 48     for(int i=0; i<12; i++) mystack1.push(i);
 49     for(int i=0; i<20; i++) mystack2.push(i);
 50 
 51     System.out.println("Stack in mystack1:");
 52     for(int i=0; i<12; i++)
 53        System.out.println(mystack1.pop());
 54 
 55     System.out.println("Stack in mystack2:");
 56     for(int i=0; i<20; i++)
 57        System.out.println(mystack2.pop());
 58   }
 59 }
 60

  1 /* Create an interface variable and
  2    access stacks through it.
  3 */
  4 class IFTest3 {
  5   public static void main(String args[]) {
  6     IntStack mystack; // create an interface reference variable
  7     DynStack ds = new DynStack(5);
  8     FixedStack fs = new FixedStack(8);
  9 
 10     mystack = ds; // load dynamic stack
 11     // push some numbers onto the stack
 12     for(int i=0; i<12; i++) mystack.push(i);
 13 
 14     mystack = fs; // load fixed stack
 15     for(int i=0; i<8; i++) mystack.push(i);
 16 
 17 
 18     mystack = ds;
 19     System.out.println("Values in dynamic stack:");
 20     for(int i=0; i<12; i++)
 21        System.out.println(mystack.pop());
 22 
 23     mystack = fs;
 24     System.out.println("Values in fixed stack:");
 25     for(int i=0; i<8; i++)
 26        System.out.println(mystack.pop());
 27   }
 28 }
 29

9.4.5 接口中的变量

  1 import java.util.Random;
  2 
  3 interface SharedConstants {
  4   int NO = 0;
  5   int YES = 1;
  6   int MAYBE = 2;
  7   int LATER = 3;
  8   int SOON = 4;
  9   int NEVER = 5;
 10 }
 11 
 12 class Question implements SharedConstants {
 13   Random rand = new Random();
 14   int ask() {
 15     int prob = (int) (100 * rand.nextDouble());
 16     if (prob < 30)
 17       return NO;           // 30%
 18     else if (prob < 60)
 19       return YES;          // 30%
 20     else if (prob < 75)
 21       return LATER;        // 15%
 22     else if (prob < 98)
 23       return SOON;         // 13%
 24     else
 25       return NEVER;        // 2%
 26   }
 27 }
 28 
 29 class AskMe implements SharedConstants {
 30   static void answer(int result) {
 31     switch(result) {
 32       case NO:
 33         System.out.println("No");
 34         break;
 35       case YES:
 36         System.out.println("Yes");
 37         break;
 38       case MAYBE:
 39         System.out.println("Maybe");
 40         break;
 41       case LATER:
 42         System.out.println("Later");
 43         break;
 44       case SOON:
 45         System.out.println("Soon");
 46         break;
 47       case NEVER:
 48         System.out.println("Never");
 49         break;
 50     }
 51   }
 52 
 53   public static void main(String args[]) {
 54     Question q = new Question();
 55     answer(q.ask());
 56     answer(q.ask());
 57     answer(q.ask());
 58     answer(q.ask());
 59   }
 60 }

9.4.6 接口可以扩展

  1 // One interface an extend another.
  2 interface A {
  3   void meth1();
  4   void meth2();
  5 }
  6 
  7 // B now includes meth1() and meth2() -- it adds meth3().
  8 interface B extends A {
  9   void meth3();
 10 }
 11 
 12 // This class must implement all of A and B
 13 class MyClass implements B {
 14   public void meth1() {
 15     System.out.println("Implement meth1().");
 16   }
 17 
 18   public void meth2() {
 19     System.out.println("Implement meth2().");
 20   }
 21 
 22   public void meth3() {
 23     System.out.println("Implement meth3().");
 24   }
 25 }
 26 
 27 class IFExtend {
 28   public static void main(String arg[]) {
 29     MyClass ob = new MyClass();
 30 
 31     ob.meth1();
 32     ob.meth2();
 33     ob.meth3();
 34   }
 35 }

9.5 默认接口方法

9.5.1 默认方法的基础知识

  1 public interface MyIF {
  2   // This is a "normal" interface method declaration. 
  3   // It does NOT define a default implementation. 
  4   int getNumber();
  5 
  6   // This is a default method. Notice that it provides 
  7   // a default implementation. 
  8   default String getString() {
  9     return "Default String";
 10   }
 11 }
 12

  1 // Implement MyIF. 
  2 class MyIFImp implements MyIF {
  3   // Only getNumber() defined by MyIF needs to be implemented. 
  4   // getString() can be allowed to default. 
  5   public int getNumber() {
  6     return 100;
  7   }
  8 }
  9

  1 // Use the default method. 
  2 class DefaultMethodDemo {
  3   public static void main(String args[]) {
  4 
  5     MyIFImp obj = new MyIFImp();
  6 
  7     // Can call getNumber(), because it is explicitly 
  8     // implemented by MyIFImp: 
  9     System.out.println(obj.getNumber());
 10 
 11     // Can also call getString(), because of default 
 12     // implementation: 
 13     System.out.println(obj.getString());
 14   }
 15 }
 16

  1 class MyIFImp2 implements MyIF {
  2   // Here, implementations for both getNumber( ) and getString( ) are provided. 
  3   public int getNumber() {
  4     return 100;
  5   }
  6 
  7   public String getString() {
  8     return "This is a different string.";
  9   }
 10 }

9.5.2 一个更加实用的例子

  1 interface IntStack {
  2   void push(int item); // store an item 
  3   int pop(); // retrieve an item 
  4 
  5   // Because clear( ) has a default, it need not be 
  6   // implemented by a preexisting class that uses IntStack. 
  7   default void clear() {
  8     System.out.println("clear() not implemented.");
  9   }
 10 }

9.5.3 多级继承的问题

9.6 在接口中使用静态方法

  1 public interface MyIF {
  2   // This is a "normal" interface method declaration. 
  3   // It does NOT define a default implementation. 
  4   int getNumber();
  5 
  6   // This is a default method. Notice that it provides 
  7   // a default implementation. 
  8   default String getString() {
  9     return "Default String";
 10   }
 11 
 12   // This is a static interface method. 
 13   static int getDefaultNumber() {
 14     return 0;
 15   }
 16 }

9.7 关于包和接口的最后说明

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原文地址：https://www.cnblogs.com/ios9/p/7518519.html

学习笔记(二)--->《Java 8编程官方参考教程（第9版）.pdf》:第七章到九章学习笔记

注：本文声明事项。

第7章 方法和类的深入分析

7.1 重载方法

7.1.1 重载构造函数

7.2 将对象用作参数

7.3 参数传递的深入分析

7.4 返回对象

7.5 递归

7.6 访问控制

7.7 理解st

7.8 final介绍

7.9 重新审视数组

7.10 嵌套类和内部类

7.11 String类介绍

7.12 使用命令行参数

7.13 varargs：可变长度参数

7.13.1 重载varargs方法

7.13.2 varargs方法与模糊性

第8章 继承

8.1 继承的基础知识

8.1.1 成员访问与继承

8.1.2 一个更实际的例子

8.1.3 超类变量可以引用子类对象

8.2 使用super关键字

8.2.1 使用super调用超类的构造函数

8.2.2 super的另一种用法

8.3 创建多级继承层次

8.4 构造函数的调用时机

8.5 方法重写

8.6 动态方法调度

8.6.1 重写方法的目的

8.6.2 应用方法重写

8.7 使用抽象类

8.8 在继承中使用final关键字

8.8.1 使用final关键字阻止重写

8.8.2 使用final关键字阻止继承

8.9 Object类

第9章 包和接口

9.1 包

9.1.1 定义包

9.1.2 包查找与CLASSPATH

9.1.3 一个简短的包示例

9.2 访问保护

9.3 导入包

9.4 接口

9.4.1 定义接口

9.4.2 实现接口

9.4.3 嵌套接口

9.4.4 应用接口

9.4.5 接口中的变量

9.4.6 接口可以扩展

9.5 默认接口方法

9.5.1 默认方法的基础知识

9.5.2 一个更加实用的例子

9.5.3 多级继承的问题

9.6 在接口中使用静态方法

9.7 关于包和接口的最后说明

第7章方法和类的深入分析

第8章继承

第9章包和接口