Java学习个人笔记（一）配置java环境变量（Feb04,2013 ）

    

    写这个个人笔记完全是出于记录自己所学，方便本人日后参考，可能很零散。这个笔记是建立在C语言编程基础上，本人学习Java只学习它与C语言不同的地方，或者我在C编程过程中很少用到的地方。所用的教材是Youtube一位达人做的视频：Java编程简明教程 by Thenewboston（Youtube）

    每次开一贴，学习Java笔记都记在这里。所写内容都是个人菜鸟级的理解，肯定错误百出。

   ---------- Oct 14, 2014 ---------

配置Java环境变量：

http://www.oracle.com/technetwork/java/javase/downloads/index.html
下载安装JDK for x86 (32bit) or x64(64bit).
右键“计算机”-属性-高级系统配置-高级-环境变量-xxx的用户变量-

变量名：JAVA_HOME
	变量值jdk的目录，例如本人：E:\Program Files\Java\jdk1.7.0_40

变量名: path 
	变量值: ;%JAVA_HOME%\bin
		;%JAVA_HOME%\jre\bin
变量名：classpath
	变量值: ;%JAVA_HOME%\lib
		;%JAVA_HOME%\lib\tools.jar 

（For my backup:）

<span style="white-space:pre">	</span>JAVA_HOME
<span style="white-space:pre">	</span>F:\Program Files\Java\jdk1.8.0_20   //java jdk 1.8
<span style="white-space:pre">	</span>C:\Program Files\Java\jdk1.7.0_67   //java jdk 1.7

<span style="white-space: pre;">	</span>path
<span style="white-space: pre;">	</span>;%JAVA_HOME%\bin;%JAVA_HOME%\jre\bin

<span style="white-space: pre;">	</span>classpath
<span style="white-space: pre;">	</span>;%JAVA_HOME%\lib;%JAVA_HOME%\lib\tools.jar

-----------------------下面检验是否配置成功，运行cmd命令，在出现的对话框输入”java“命令，如果出现以下结果，则表明配置成功。------------

用法: java [-options] class [args...]
           (执行类)
   或  java [-options] -jar jarfile [args...]
           (执行 jar 文件)
其中选项包括:
    -d32          使用 32 位数据模型 (如果可用)
    -d64          使用 64 位数据模型 (如果可用)
    -client       选择 "client" VM
    -server       选择 "server" VM
                  默认 VM 是 client.
。。。
------
------
运行cmd命令，
在出现的对话框输入”javac“命令，出现以下结果，表明配置成功：
	C:\Users\LENOVO>javac
	用法: javac <options> <source files>

   ---------- Feb 04, 2013 ---------

    个人理解：Java 的基本架构是通过class建立。class相当于C函数集，每个Class 里面的 method 相当于C的函数。

    1. 关于Class 中对别的class中的method的使用，创建：

        题目：main method在apple.java apple class中，引用tuna class中的println(); method, 输出一行字。
理解：对象的创建与使用。System.out.println() 的使用。

//file: project/apples.java
class apples{
	public static void main(String args[]){
		tuna tunaObj = new tuna();    //create an obj: "tuna" - class name, tunaObj-Obj name, 
		tunaObj.MysimpleMessage();
	}
}

//file: project/tuna.java
public class tuna{
	public void MysimpleMessage(){
	System.out.println("This is class tuna");		
	}
}

    2. 题目：创建和使用Scanner对象，以从键盘获取输入：

//file: project/apples.java
import java.util.Scanner;

class apples{
	public static void main(String args[]){
		Scanner input = new Scanner(System.in);  //creat an scanner obj
		tuna tunaObj = new tuna();    //create an obj: "tuna" - class name, tunaObj-Obj name, 

		System.out.println("Enter your name here: ");
		String name = input.nextLine();

		tunaObj.MysimpleMessage(name);
	}

}

//file: project/tuna.java
public class tuna{
	public void MysimpleMessage(String name){
	System.out.println("Hello" + name);
	}
}

    3. 从main method传递值到别的class的method中：
要求：通过 GetName method 把 name 传递进class tuna中，通过tuna中的saying method 内部调用ret_name method 打印出 name.
本实例理解：1、在method内部声明变量和在class内声明变量有何不同。
2、class 内部互相调用method
3、跨 class 调用method

//----------------------- tutorial 16
//file: project/apples.java
import java.util.Scanner;

class apples{
	// Create a method named "main" Type"void":
	public static void main(String args[]){
		//Create method body:
		//Create a Scanner Obj:
		Scanner input = new Scanner(System.in);
		//Create a tuna Obj:
		tuna tunaObj = new tuna();
		String name;
		
		System.out.println("Enter your name here: ");
		//wait usr to input a string:  
		name = input.nextLine();
		tunaObj.GetName(name);
		
		//call class, use method MysimpleMessage();
		tunaObj.saying();
	}
}

//file: project/tuna.java
public class tuna {
		private String girlname;
		
		public void GetName(String name){
			girlname = name;
		}
		
		public String retName(){
			return girlname;
		}
		
		public void saying(){
			System.out.printf("your name: %s",retName());		
		}
}

    4. Constructor的使用，用于创建对class_Obj的使用时，同时设置class_Obj的初始参数。比如一个班的学生的姓名，年龄等。

·理解Constructor的作用，出现的位置。它用于在初始化obj时设置参数，所以应该在非主class中。
·Constructor的声明形式：它有点像声明一个method，但是没有返回类型。constructor的名称与class名须一致。Constructor体内多是赋值符。
·副class结构：从本例可以看出，一个副class的结构大致为： class名-> class private variable 声明 -> Constructor声明 -> methods声明 （熟悉基本结构很重要）
·Constructor在主class中被使用时的语法。要注意。

//----------------------- tutorial 17
//file: project/apples.java
class apples{
	// Create a method named "main" Type"void":
	public static void main(String args[]){
		tuna tunaObj1 = new tuna("Amily",16);
		tuna tunaObj2 = new tuna("Banry",19);
		
		tunaObj1.saying();
		tunaObj2.saying();
				
	}	
}

//file: project/tuna.java
public class tuna{
	private String girlname;
	private int girlage;
	
	public tuna(String name, int age){    //Create constructor, this "tuna" is exactly the name of this class
		girlname = name;
		girlage  = age;
	}
	
/*	public void GetNmae(String name){
		girlname = name;		
	}*/
	
	public String retName(){
		return girlname;
	}
	
	public void saying(){
		System.out.printf("Your name is: %s, Age: %d \n", retName(), girlage);
		
	}
}

     5.  Java中使用 " （（条件判断） ？ 语句1 ：语句2） " 替代并简化if条件判断语句：

//----------------------- tutorial 36/37 Display Regurlar Time
//file: project/apples.java

class apples{
	// Create a method named "main" Type"void":
	public static void main(String args[]){
		
		tuna tunaObj = new tuna();
		tunaObj.setTime(14, 56, 20);
		System.out.println(tunaObj.dispTime());
		System.out.println(tunaObj.dispRegTime());

	}	
}

//file: project/tuna.java
public class tuna{
	private int hour;
	private int minute;
	private int second;
	
	public void setTime(int h, int m, int s){
		hour = ((h>=0 && h<=24) ? h : 0);    //equivalent with"  if (h>=0 && h<=24)  {hour = h;} else {hour = 0;} 
		minute = ((m>=0 && m<=60) ? m : 0);
		second = ((s>=0 && s<=60) ? s : 0);
	}
	
	public String dispTime(){
		return String.format("%02d:%02d:%02d", hour, minute, second);
	}
	public String dispRegTime(){
		return String.format("%d:%02d:%02d  %s", 
				((hour<=12) ? hour : hour%12), minute, second, ((hour>12) ? "PM" : "AM"));
	}
}

    6.  Java中this关键字，public /private概念。当constructor 中arguments 和 variable 的名称完全一样时候，用this可以指明调用哪一个值。

//----------------------- Tutorial - 38 - Public, Private and this
//file: project/apples.java
class apples{
	// Create a method named "main" Type"void":
	public static void main(String args[]){
		
		tuna tunaObj = new tuna();
		
		System.out.println(tunaObj.dispTime());
		//System.out.println(tunaObj.dispRegTime());
		
		tunaObj.setTime(14, 56, 20);
		
		System.out.println(tunaObj.dispTime());
		//System.out.println(tunaObj.dispRegTime());

	}	
}

//file: project/tuna.java
public class tuna{
	private int hour = 1;
	private int minute = 2;
	private int second = 3;
	
	public void setTime(int hour, int minute, int second){
		this.hour = hour;
		this.minute = 5;    // Use the value of 5 when minute is called by dispTime() method
		second = 6;         // Use the value of 3 when second is called by dispTime() method

//		hour = ((h>=0 && h<=24) ? h : 0);
//		minute = ((m>=0 && m<=60) ? m : 0);
//		second = ((s>=0 && s<=60) ? s : 0);
	}
	
	public String dispTime(){
		return String.format("%02d:%02d:%02d", hour, minute, second);
	}
	public String dispRegTime(){
		return String.format("%d:%02d:%02d  %s", 
				((hour<=12) ? hour : hour%12), minute, second, ((hour>12) ? "PM" : "AM"));
	}
}

    7. Constructor 的嵌套使用，适用于constructor输入参数个数不确定的情形：

//----------------------- tutorial 40/41 - Building Objects for Constructors
//file: project/apples.java
class apples{
	public static void main(String[] args){
		//create 4 diff objs as there are 4 diff constructor
		tuna tunaObj0 = new tuna();
		tuna tunaObj1 = new tuna(5);
		tuna tunaObj2 = new tuna(5,13);
		tuna tunaObj3 = new tuna(5,13,14);
		
		//use the objs
		System.out.printf("%s\n",tunaObj0.toMilitary());
		System.out.printf("%s\n",tunaObj1.toMilitary());
		System.out.printf("%s\n",tunaObj2.toMilitary());
		System.out.printf("%s\n",tunaObj3.toMilitary());
	}

}

//file: project/tuna.java
public class tuna{
	private int hour;
	private int minute;
	private int second;
	
	public tuna(){
		this(0,0,0);
	}
	public tuna(int h){
		this(h,0,0);
	}
	public tuna(int h, int m){
		this(h,m,0);
	}
	public tuna(int h, int m, int s){
		setTime(h,m,s);
	}
		
	public void setTime(int h, int m, int s){
		setHour(h);
		setMinute(m);
		setSecond(s);
	}
	public void setHour(int h){
		hour = ((h>=0 && h<24)? h: 0);
	}
	public void setMinute(int m){
		minute = ((m>=0 && m<60)? m: 0);
	}
	public void setSecond(int s){
		second = ((s>=0 && s<60)? s: 0);
	}
	public int getHour(){
		return hour;
	}
	public int getMinute(){
		return minute;
	}
	public int getSecond(){
		return second;
	}
	public String toMilitary(){
		return String.format("%02d:%02d:%02d",getHour(),getMinute(),getSecond());
	}
}

     8. 比较复杂一个例子。

1）关于toString() method的使用。在potpie class中，每次声明使用potpie class时，由于其中constructor 语句里具有一个“

System.out.printf("The constructor for this is %s \n", this);

” ，所以每次声明都会打印一句The constructor for this is .xxx ,xxx的内容就调用this. this 会指向the following "toString()" method. 

        2）在tuna class中声明并使用了一个 potpie object，这个object是由第6行的语句传递进去的，第16行的（potpie birthday）语句定义了它的入口。

        3）tuna class 继续使用toString method来服务 apples class 中 main method 中 System.out.println(tunaObj);语句对它的调用。

        明显感觉我还对toString() method 的使用理解不够深入。包括 this 和 toString 的配合使用。

//----------------- tutorial 42 toString methods, 43-Composition
//file: project/apples.java
class apples{
	public static void main(String[] args){
		potpie potObj = new potpie(4,5,2006);
		tuna tunaObj = new tuna("Jack",potObj); //take the potObj just built up
		System.out.println(tunaObj);
	}
}

//file: project/tuna.java
public class tuna{
	private String name;
	private potpie date;
	
	public tuna(String theName, potpie birthday){
		name = theName;
		date = birthday;
	}
	
	public String toString(){
		return String.format("Your name is %s, and birthday is %s", name, date);
	}
}

//file: project/potpie.java
public class potpie {
	
	private int month;
	private int day;
	private int year;
	
	public potpie(int m, int d, int y){
		month = m;
		day   = d;
		year  = y;
		
		System.out.printf("The constructor for this is %s \n", this);
		//this is a reference to the obj we just built whenever we call this class
	}
	public String toString(){
		return String.format("%d/%d/%d",month,day,year);
	}
}

    

    9. 枚举类型enum的使用。

//----------------------- tutorial 44/45 Enumeration 枚举
//file: project/apples.java
//import java.utile.EnumSet;   // enable to use EnumSet.rang(from,to);
class apples{
	public static void main(String[] args){
		for (tuna people : tuna.values())
			System.out.printf("%s\t%s\t%s \n", 
					people, people.getDesc(),people.getYear());
		System.out.println("\n And now for the range of constants!\n");
		
//		for (tuna people: EnumSet.range(tuna.kelsey,tuna.candy))   // pick up part of the members from tuna
//			System.out.printf("%s\t%s\t%s \n", 
//					people, people.getDesc(),people.getYear());
		
		
	}
}

//file: project/tuna.java
public enum tuna{            // change class into enum
	// enu constants/obj:
	bucky("nice","22"),
	kelsey("cutie","10"),
	julia("bigmistake", "12"),
	nicole("italian","13"),
	candy("different","14"),
	erin("iwish","16");
	
	private final String desc;  // variable(String)
	private final String year;
	
	// build enum constructor
	tuna(String description, String birthday){
		desc = description;
		year = birthday;
	}
	
	public String getDesc(){
		return desc;
	}
	public String getYear(){
		return year;
	}
}

10. 关于Static的用法：（此处包含变量的static和method的static）

//----------------------- tutorial 46/47 Static
//file: project/apples.java
//file: project/apples.java
class apples{
	public static void main(String[] args){
		tuna member1 = new tuna("Megan","Fox");
		tuna member2 = new tuna("Natalie","Portman");
		
		System.out.println("----------------");
		
		System.out.println(member1.getFirst());
		System.out.println(member1.getLast());
		System.out.println(member1.getMembers());  
		System.out.println(   tuna.getsMembers()); //getsMembers() is a static method
		
	}
}

//file: project/tuna.java
public class tuna{
	private String first;
	private String last;
	private static int members = 0;   //static variable, like "in-class globel variable"

	public tuna(String fn,String ln) {
		first = fn;
		last  = ln;
		members++;
		System.out.printf("Constructor for %s %s, members in the club: %d\n",first,last,members);
	}
	public String getFirst(){
		return first;
	}
	public String getLast(){
		return last;
	}
	public int getMembers(){
		return members;
	}
	public static int getsMembers(){
		return members;
	}
}

    11. final的理解和用法：

//----------------------- tutorial 48 final
//file: project/apples.java
class apples{
	public static void main(String[] args){
		tuna tunaObj = new tuna(10);
		tuna tunaObj2= new tuna(1);
		
		for(int i = 0; i<3 ; i++){
			tunaObj.add();
			System.out.printf("%s",tunaObj);
		}
		System.out.println("-------------");
		for(int i = 0; i<3 ; i++){
			tunaObj2.add();
			System.out.printf("%s",tunaObj2);
		}
	}
}

//file: project/tuna.java
public class tuna{
	private int sum;
	private final int NUMBER;

	public tuna(int x){
		NUMBER = x;  // you can only modify it once in one class
		//NUMBER = 5;  //can not change its value again
	}
	public void add(){
		sum+=NUMBER;
	}
	public String toString(){
		return String.format("sum = %d\n",sum);
	}
}

    12. Inheritance -- 继承 ，这是我接触到的新概念。 什么是java 的继承？  1）被继承的class叫做super class, super class 中private的变量和method不能被继承。  2）继承的class中如果method名与super class中的method名重合，则使用继承object时，运行继承class中重合的method代码，即以继承class 为准。此谓overwrite.

//----------------------- tutorial 49 Inheritance 继承
//----------------------- tutorial 49 Inheritance 继承
//file: project/apples.java
class apples{
	public static void main(String[] args){
		tuna tunaObj = new tuna();
		potpie potpieObj = new potpie();

		System.out.println("--- tunaObj.eat() ---");
		tunaObj.eat();
		System.out.println("--- potpieObj.drink() ---");
		potpieObj.drink();
		System.out.println("--- potpieObj.potpiemethod() ---");
		potpieObj.potmethod();
	}
}

//file: project/food.java  //super class
public class food{
	public void eat(){
		System.out.println("I am eat methods from food");
	}
	public void drink(){
		System.out.println("I am drink methods from food");
	}
	private void bite(){     //private methods cannot be inheritance
		System.out.println("I am bite methods from food");
	}
}

//file: project/tuna.java
public class tuna extends food{ // Inheriance from food
	public void eat(){
		System.out.println("tuna overwritten eas() of food");		
	}
}

//file: project/potpie.java
public class potpie extends food{ // Inheritance from food
	public void potmethod(){
		System.out.println("I am potmethod from potpie");
	}
}

    13.