201871020225-牟星源《面向对象程序设计（java）》第七周学习总结
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https://www.cnblogs.com/nwnu-daizh/ |
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https://www.cnblogs.com/nwnu-daizh/p/11435127.html |
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随笔博文正文内容：
实验内容和步骤
实验1：在“System.out.println(...);”语句处按注释要求设计代码替换...，观察代码录入中IDE提示，以验证四种权限修饰符的用法。
(1)程序代码
实验代码：
class Parent {
private String p1 = "这是Parent的私有属性";
public String p2 = "这是Parent的公有属性";
protected String p3 = "这是Parent受保护的属性";
String p4 = "这是Parent的默认属性";
private void pMethod1() {
System.out.println("我是Parent用private修饰符修饰的方法");
}
public void pMethod2() {
System.out.println("我是Parent用public修饰符修饰的方法");
}
protected void pMethod3() {
System.out.println("我是Parent用protected修饰符修饰的方法");
}
void pMethod4() {
System.out.println("我是Parent无修饰符修饰的方法");
}
}
class Son extends Parent{
private String s1 = "这是Son的私有属性";
public String s2 = "这是Son的公有属性";
protected String s3 = "这是Son受保护的属性";
String s4 = "这是Son的默认属性";
public void sMethod1() {
System.out.println(p2);//分别尝试显示Parent类的p1、p2、p3、p4值
System.out.println("我是Son用public修饰符修饰的方法");
}
private void sMethod2() {
System.out.println("我是Son用private修饰符修饰的方法");
}
protected void sMethod3() {
System.out.println("我是Son用protected修饰符修饰的方法");
}
void sMethod4() {
System.out.println("我是Son无修饰符修饰的方法");
}
}
public class Demo {
public static void main(String[] args) {
Parent parent=new Parent();
Son son=new Son();
parent.pMethod2() ; //分别尝试用parent调用Paren类的方法、用son调用Son类的方法
}
}
parent代码:
package mxy;
public class Parent {
private String p1 = "这是Parent的私有属性";
public String p2 = "这是Parent的公有属性";
protected String p3 = "这是Parent受保护的属性";
String p4 = "这是Parent的默认属性";
private void pMethod1() {
System.out.println("我是Parent用private修饰符修饰的方法");
}
public void pMethod2() {
System.out.println("我是Parent用public修饰符修饰的方法");
}
protected void pMethod3() {
System.out.println("我是Parent用protected修饰符修饰的方法");
}
void pMethod4() {
System.out.println("我是Parent无修饰符修饰的方法");
}
}
son代码：
package first;
import mxy.Parent;
public class Son extends Parent{
private String s1 = "这是Son的私有属性";
public String s2 = "这是Son的公有属性";
protected String s3 = "这是Son受保护的属性";
String s4 = "这是Son的默认属性";
public void sMethod1() {
System.out.println(p2);//分别尝试显示Parent类的p1、p2、p3、p4值
System.out.println("我是Son用public修饰符修饰的方法");
}
private void sMethod2() {
System.out.println("我是Son用private修饰符修饰的方法");
}
protected void sMethod3() {
System.out.println("我是Son用protected修饰符修饰的方法");
}
void sMethod4() {
System.out.println("我是Son无修饰符修饰的方法");
}
}
(2)运行结果如下：
Parent1:
Parent2:
Parent3：
Parent4：
Son1：
Son2：
Son3：
Son4：
实验2：导入第5章以下示例程序，测试并进行代码注释。
实验2：测试程序1
l 运行教材程序5-8、5-9、5-10，结合程序运行结果理解程序（教材174页-177页）；
5.8代码：
package equals;
/**
* This program demonstrates the equals method.
* @version 1.12 2012-01-26
* @author Cay Horstmann
*/
public class EqualsTest
{
public static void main(String[] args)
{
Employee alice1 = new Employee("Alice Adams", 75000, 1987, 12, 15);
Employee alice2 = alice1;
Employee alice3 = new Employee("Alice Adams", 75000, 1987, 12, 15);
Employee bob = new Employee("Bob Brandson", 50000, 1989, 10, 1);
System.out.println("alice1 == alice2: " + (alice1 == alice2));
System.out.println("alice1 == alice3: " + (alice1 == alice3));
System.out.println("alice1.equals(alice3): " + alice1.equals(alice3));
System.out.println("alice1.equals(bob): " + alice1.equals(bob));
System.out.println("bob.toString(): " + bob);
Manager carl = new Manager("Carl Cracker", 80000, 1987, 12, 15);
Manager boss = new Manager("Carl Cracker", 80000, 1987, 12, 15);
boss.setBonus(5000);
System.out.println("boss.toString(): " + boss);
System.out.println("carl.equals(boss): " + carl.equals(boss));
System.out.println("alice1.hashCode(): " + alice1.hashCode());
System.out.println("alice3.hashCode(): " + alice3.hashCode());
System.out.println("bob.hashCode(): " + bob.hashCode());
System.out.println("carl.hashCode(): " + carl.hashCode());
}
}
5.9代码：
package equals;
import java.time.*;
import java.util.Objects;
public class Employee
{
private String name;
private double salary;
private LocalDate hireDay;
public Employee(String name, double salary, int year, int month, int day)
{
this.name = name;
this.salary = salary;
hireDay = LocalDate.of(year, month, day);
}
public String getName()
{
return name;
}
public double getSalary()
{
return salary;
}
public LocalDate getHireDay()
{
return hireDay;
}
public void raiseSalary(double byPercent)
{
double raise = salary * byPercent / 100;
salary += raise;
}
public boolean equals(Object otherObject)
{
// a quick test to see if the objects are identical
if (this == otherObject) return true;
// must return false if the explicit parameter is null
if (otherObject == null) return false;
// if the classes don't match, they can't be equal
if (getClass() != otherObject.getClass()) return false;
// now we know otherObject is a non-null Employee
Employee other = (Employee) otherObject;
// test whether the fields have identical values
return Objects.equals(name, other.name)
&& salary == other.salary && Objects.equals(hireDay, other.hireDay);
}
public int hashCode()
{
return Objects.hash(name, salary, hireDay);
}
public String toString()
{
return getClass().getName() + "[name=" + name + ",salary=" + salary + ",hireDay="
+ hireDay + "]";
}
}
5.10代码：
package equals;
public class Manager extends Employee
{
private double bonus;
public Manager(String name, double salary, int year, int month, int day)
{
super(name, salary, year, month, day);
bonus = 0;
}
public double getSalary()
{
double baseSalary = super.getSalary();
return baseSalary + bonus;
}
public void setBonus(double bonus)
{
this.bonus = bonus;
}
public boolean equals(Object otherObject)
{
if (!super.equals(otherObject)) return false;
Manager other = (Manager) otherObject;
// super.equals checked that this and other belong to the same class
return bonus == other.bonus;
}
public int hashCode()
{
return java.util.Objects.hash(super.hashCode(), bonus);
}
public String toString()
{
return super.toString() + "[bonus=" + bonus + "]";
}
}
运行结果：
l 删除程序中Employee类、Manager类中的equals()、hasCode()、toString()方法，背录删除方法，在代码录入中理解类中重写Object父类方法的技术要点。
(1)代码
Employee类重写后代码如下：
package equals;
import java.time.*;
import java.util.Objects;
public class Employee
{
private String name; //创建三个私有属性
private double salary;
private LocalDate hireDay;
public Employee(String name, double salary, int year, int month, int day)
{
this.name = name;
this.salary = salary;
hireDay = LocalDate.of(year, month, day);
}
public String getName()
{
return name;
}
public double getSalary()
{
return salary;
}
public LocalDate getHireDay()
{
return hireDay;
}
public void raiseSalary(double byPercent)
{
double raise = salary * byPercent / 100; //定义局部变量
salary += raise;
}
@Override
public int hashCode() { //重写hashCode方法，使相等的两个对象获取的HashCode也相等
// TODO Auto-generated method stub
return Objects.hash(name, salary, hireDay);
}
@Override
public boolean equals(Object obj) {
// TODO Auto-generated method stub
if (this == obj) return true; //快速测试几个类的根是否相同，即是否是同一个超类。这个if语句判断两个引用是否是同一个，如果是同一个，那么这两个对象肯定相等。
if (obj == null) return false; //如果显示参数为空，则返回false
if (getClass() !=obj.getClass()) return false; //用getClass（）方法得到对象的类。如果几个类不匹配，则它们不相等
//其他对象是非空Employee类
//在以上判断完成，再将得到的参数对象强制转换为该对象，考虑到父类引用子类的对象的出现，然后再判断对象的属性是否相同
Employee other = (Employee) obj;
//测试字段是否具有相同的值
return Objects.equals(name, other.name) && salary == other.salary && Objects.equals(hireDay, other.hireDay);
}
@Override
public String toString() { //把其他类型的数据转为字符串类型的数据（toString方法可以自动生成）
// TODO Auto-generated method stub
return getClass().getName() + "[name=" + name + ",salary=" + salary + ",hireDay=" + hireDay + "]";
}
}
Manager类重写之后代码如下：
package equals;
public class Manager extends Employee //子类：Manager类继承Employee类
{
private double bonus; //创建私有属性bouns
public Manager(String name, double salary, int year, int month, int day)
{
super(name, salary, year, month, day); //子类直接调用超类中已创建的属性
bonus = 0; //给bouns赋初值为空
}
public double getSalary()//访问器
{
double baseSalary = super.getSalary();
return baseSalary + bonus;
}
public void setBonus(double bonus) //更改器
{
this.bonus = bonus;
}
public boolean equals(Object otherObject) //快速测试几个类的根是否相同，即是否是同一个超类
{
if (!super.equals(otherObject)) return false;
Manager other = (Manager) otherObject;
//使用super.equals检查这个类和其他是否属于同一个类
return bonus == other.bonus;
}
public int hashCode() //重写hashCode方法，使相等的两个对象获取的HashCode也相等
{
return java.util.Objects.hash(super.hashCode(), bonus);
}
public String toString() //把其他类型的数据转为字符串类型的数据（toString方法可以自动生成）
{
return super.toString() + "[bonus=" + bonus + "]";
}
}
EmployeeTest类代码如下：
package equals;
/**
* This program demonstrates the equals method.
* @version 1.12 2012-01-26
* @author Cay Horstmann
*/
public class EqualsTest
{
public static void main(String[] args)
{
Employee alice1 = new Employee("Alice Adams", 75000, 1987, 12, 15);
Employee alice2 = alice1;
Employee alice3 = new Employee("Alice Adams", 75000, 1987, 12, 15);
Employee bob = new Employee("Bob Brandson", 50000, 1989, 10, 1);
System.out.println("alice1 == alice2: " + (alice1 == alice2));
System.out.println("alice1 == alice3: " + (alice1 == alice3));
System.out.println("alice1.equals(alice3): " + alice1.equals(alice3));
System.out.println("alice1.equals(bob): " + alice1.equals(bob));
System.out.println("bob.toString(): " + bob);
Manager carl = new Manager("Carl Cracker", 80000, 1987, 12, 15);
Manager boss = new Manager("Carl Cracker", 80000, 1987, 12, 15);
boss.setBonus(5000);
System.out.println("boss.toString(): " + boss);
System.out.println("carl.equals(boss): " + carl.equals(boss));
System.out.println("alice1.hashCode(): " + alice1.hashCode());
System.out.println("alice3.hashCode(): " + alice3.hashCode());
System.out.println("bob.hashCode(): " + bob.hashCode());
System.out.println("carl.hashCode(): " + carl.hashCode());
}
}
(2)运行结果如下：
实验2：测试程序2
l 在elipse IDE中调试运行程序5-11（教材182页），结合程序运行结果理解程序；
l 掌握ArrayList类的定义及用法；
l 在程序中相关代码处添加新知识的注释；
5.11代码：
package arrayList;
import java.util.*;
/**
* This program demonstrates the ArrayList class.
* @version 1.11 2012-01-26
* @author Cay Horstmann
*/
public class ArrayListTest
{
public static void main(String[] args)
{
// fill the staff array list with three Employee objects
ArrayList staff = new ArrayList<Employee>();
staff.add(new Employee("Carl Cracker", 75000, 1987, 12, 15));
staff.add(new Employee("Harry Hacker", 50000, 1989, 10, 1));
staff.add(new Employee("Tony Tester", 40000, 1990, 3, 15));
// raise everyone's salary by 5%
for (Employee e : staff)
e.raiseSalary(5);
// print out information about all Employee objects
for (Employee e : staff)
System.out.println("name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay="
+ e.getHireDay());
}
}
package arrayList;
import java.time.*;
public class Employee
{
private String name;
private double salary;
private LocalDate hireDay;
public Employee(String name, double salary, int year, int month, int day)
{
this.name = name;
this.salary = salary;
hireDay = LocalDate.of(year, month, day);
}
public String getName()
{
return name;
}
public double getSalary()
{
return salary;
}
public LocalDate getHireDay()
{
return hireDay;
}
public void raiseSalary(double byPercent)
{
double raise = salary * byPercent / 100;
salary += raise;
}
}
运行结果：
l 设计适当的代码，测试ArrayList类的set()、get()、remove()、size()等方法的用法。
代码为：
package arrayList;
import java.util.*;
/**
* This program demonstrates the ArrayList class.
* @version 1.11 2012-01-26
* @author Cay Horstmann
*/
public class ArrayListTest
{
private static final Employee element = null;
private static final int index = 0;
public static void main(String[] args)
{
// fill the staff array list with three Employee objects
ArrayList<Employee> staff = new ArrayList<Employee>(); //用三个Employee对象填充数组
staff.add(new Employee("Carl Cracker", 75000, 1987, 12, 15));
staff.add(new Employee("Harry Hacker", 50000, 1989, 10, 1));
staff.add(new Employee("Tony Tester", 40000, 1990, 3, 15));
ArrayList<Employee> list = new ArrayList<Employee>();
//size()的用法
int size=staff.size();
System.out.println("arrayList中的元素个数是："+size);
for(int i=0;i<staff.size();i++)
{
//get()的用法
Employee e=staff.get(i);
System.out.println("name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay="
+ e.getHireDay());
}
//set()的用法
staff.set(0, new Employee("llx", 20000, 1999, 11, 06));
Employee e=staff.get(0);
System.out.println("修改后的数据为：name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay="
+ e.getHireDay());
//remove()的用法
staff.remove(2);
System.out.println("将第一个数据删除后：");
int size1=staff.size();
System.out.println("arrayList中的元素个数是："+size1);
for(int i=0;i<staff.size();i++)
{
Employee p=staff.get(i);
System.out.println("name=" + p.getName() + ",salary=" + p.getSalary() + ",hireDay="
+ p.getHireDay());
}
// raise everyone's salary by 5%
for (Employee e1 : staff) //把每个人的薪资提高%5
e1.raiseSalary(5);
// print out information about all Employee objects
for (Employee e1 : staff) //输出所有雇员对象的信息
System.out.println("name=" + e1.getName() + ",salary=" + e1.getSalary() + ",hireDay="
+ e1.getHireDay()); //利用getName()，getSalary() 和getHireDay()方法输出所有雇员对象的信息
}
}
运行结果：
实验2：测试程序3
l 编辑、编译、调试运行程序5-12（教材189页），结合运行结果理解程序；
l 掌握枚举类的定义及用法；
l 在程序中相关代码处添加新知识的注释；
代码为：
package enums;
import java.util.*;
/**
* This program demonstrates enumerated types.
* @version 1.0 2004-05-24
* @author Cay Horstmann
*/
public class EnumTest
{
public static void main(String[] args)
{
Scanner in = new Scanner(System.in);
System.out.print("Enter a size: (SMALL, MEDIUM, LARGE, EXTRA_LARGE) ");
String input = in.next().toUpperCase();
Size size = Enum.valueOf(Size.class, input);
System.out.println("size=" + size);
System.out.println("abbreviation=" + size.getAbbreviation());
if (size == Size.EXTRA_LARGE)
System.out.println("Good job--you paid attention to the _.");
}
}
enum Size
{
SMALL("S"), MEDIUM("M"), LARGE("L"), EXTRA_LARGE("XL");
private Size(String abbreviation) { this.abbreviation = abbreviation; }
public String getAbbreviation() { return abbreviation; }
private String abbreviation;
}
运行结果为：
l 删除程序中Size枚举类，背录删除代码，在代码录入中掌握枚举类的定义要求。
代码为：
package enums;
import java.util.*;
/**
* This program demonstrates enumerated types.
* @version 1.0 2004-05-24
* @author Cay Horstmann
*/
public class EnumTest
{
public static void main(String[] args)
{
var in = new Scanner(System.in);
System.out.print("Enter a size: (SMALL, MEDIUM, LARGE, EXTRA_LARGE) ");
String input = in.next().toUpperCase();
Size size = Enum.valueOf(Size.class, input); //静态values方法返回枚举的所有值的数组
System.out.println("size=" + size);
System.out.println("abbreviation=" + size.getAbbreviation());
if (size == Size.EXTRA_LARGE)
System.out.println("Good job--you paid attention to the _.");
}
}
enum Size
{
SMALL("S"), MEDIUM("M"), LARGE("L"), EXTRA_LARGE("XL");
private Size(String abbreviation) { this.abbreviation = abbreviation; }
public String getAbbreviation() { return abbreviation; }
private String abbreviation;
}//调用构造函数
运行结果为：
实验2：测试程序4
录入以下代码，结合程序运行结果了解方法的可变参数用法
|
public class TestVarArgus { public static void dealArray(int... intArray){ for (int i : intArray) System.out.print(i +" ");
System.out.println(); } public static void main(String args[]){ dealArray(); dealArray(1); dealArray(1, 2, 3); } } |
代码为：
public class TestVarArgus {
public static void dealArray(int... intArray){
for (int i : intArray)
System.out.print(i +" ");
System.out.println();
}
public static void main(String args[]){
dealArray();
dealArray(1);
dealArray(1, 2, 3);
}
}
运行结果：
实验3：编程练习
参照输出样例补全程序，使程序输出结果与输出样例一致。
|
public class Demo { public static void main(String[] args) { Son son = new Son(); son.method(); } } class Parent { Parent() { System.out.println("Parent's Constructor without parameter"); } Parent(boolean b) { System.out.println("Parent's Constructor with a boolean parameter"); } public void method() { System.out.println("Parent's method()"); } } class Son extends Parent { //补全本类定义 } |
程序运行结果如下：
Parent's Constructor with a boolean parameter
Son's Constructor without parameter
Son's method()
Parent's method()
代码为：
public class TestVarArgus {
public static void dealArray(int... intArray){
for (int i : intArray)
System.out.print(i +" ");
System.out.println();
}
public static void main(String args[]){
dealArray();
dealArray(1);
dealArray(1, 2, 3);
}
}
运行结果为：
3. 实验总结：（15分）
本次试验学习了访问修饰符有四种public protected 默认的不写的 private，public 访问权限最大，同包（同文件夹）里面的类绝对是可以互相访问的，不同包中的类只要经过import得到了路径后也是可以通过类的对象访问的，protected 和 默认的比public访问权限都要小（不能在其他包中被访问除非继承这里是指protected）但他们两之间有细微的区别就是在不同包中的类继承protected和 默认的时候 ,继承的类能够访问用protected修饰的成员而不能访问默认即不写修饰符的成员，private 范围最小 只能在类内部的成员之间进行访问，外部的类是绝对没有办法通过对象访问到私有成员的,继承的类也不会继承private的成员在Java中，ArrayList类可以解决运行时动态更改数组的问题。ArrayList使用起来有点像数组，但是在添加或删除元素时，具有自动调节数组容量的功能，而不需要为此编写任何代码。在今后的学习中要多思考，多去理解代码，理解各种参数的使用方法。多进行编程练习，以提高编程能力。