ThreadLocal的练习代码

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场景:

有三个小孩儿,买了一个变形金刚玩具(Transformer)....

三个小孩都争着玩这个玩具....没有一个人可以玩...

第一种方式:每个人各玩一会....

第二种方式:再买两个玩具,一个人玩一个.

每个小孩都当成一个线程.三个小孩就有三个线程.

Child.java

 import java.util.Random;
 import java.util.concurrent.TimeUnit;

 public class Child implements Runnable{
     private Transformer2 transformer;

     private String name ;

     public Child(Transformer2 transformer) {
         this.transformer = transformer;
     }

     public Child() {
     }

     public Transformer2 getTransformer() {
         return transformer;
     }

     public void setTransformer(Transformer2 transformer) {
         this.transformer = transformer;
     }

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public void play(){

         while (true) {
             try {
                 //transformer = new Transformer();//每次调用该方法，该对象都是新的。

                 //想要的效果是每个小孩儿都有一个玩具,但是不管他玩多少次,这个玩具永远都是唯一的.
                 transformer = Transformer2.getInstance();
                 System.out.println(Thread.currentThread().getName() +" :"+transformer );
                 String str = "擎天柱" + new Random().nextInt(10);
                 System.out.println(Thread.currentThread().getName()
                         + ": 将变形金刚设置成 ：" + str);
                 transformer.setType(str);
                 TimeUnit.SECONDS.sleep(2);

                 String type = transformer.getType();

                 System.out.println(Thread.currentThread().getName()
                         + ": 获取到的变形金刚是：" + type);

             } catch (InterruptedException e) {
                 e.printStackTrace();
             }
         }

     }

     @Override
     public void run() {
         play();
     }

 }

Transformer.java

 import java.util.HashMap;
 import java.util.Map;

 /*
  * 每个线程都有且仅有一个 该类对象的引用。
  * 不应该在外部类中随便的去new 所以构造方法私有
  *
  */
 public class Transformer {

     private static Map<Thread, Transformer> maps = new HashMap<Thread, Transformer>();

     private String type;

     private Transformer(){}

     public static Transformer getInstance() {
         Transformer instance = maps.get(Thread.currentThread());
         if(instance == null) {
             instance = new Transformer();
             maps.put(Thread.currentThread(),instance);
         }
         return instance;
     }
     public String getType() {
         return type;
     }

     public void setType(String type) {
         this.type = type;
     }

 }

Transformer2.java(使用ThreadLocal类)

 import java.util.HashMap;
 import java.util.Map;

 /*
  * 每个线程都有且仅有一个 该类对象的引用。
  *
  */
 public class Transformer2 {

     //private static Map<Thread, Transformer2> maps = new HashMap<Thread, Transformer2>();
     private static ThreadLocal<Transformer2> maps = new ThreadLocal<Transformer2>();

     private String type;

     private Transformer2(){}

     public static Transformer2 getInstance() {
         Transformer2 instance = maps.get();
         if(instance == null) {
             instance = new Transformer2();
             maps.set(instance);
         }
         return instance;
     }
     public String getType() {
         return type;
     }

     public void setType(String type) {
         this.type = type;
     }
 }

测试类:

 public class Test {

     public static void main(String[] args) {

         //Transformer transformer = new Transformer();

         for (int i = 0; i < 3; i++) {
             new Thread(new Child()).start();
         }
     }
 }