ThreadLocal的練習代碼

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場景:

有三個小孩兒,買了一個變形金剛玩具(Transformer)....

三個小孩都爭著玩這個玩具....沒有一個人可以玩...

第一種方式:每個人各玩一會....

第二種方式:再買兩個玩具,一個人玩一個.

每個小孩都當成一個線程.三個小孩就有三個線程.

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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();//每次調用該方法，該對象都是新的。
                
                //想要的效果是每個小孩兒都有一個玩具,但是不管他玩多少次,這個玩具永遠都是唯一的.
                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()
                        + ": 將變形金剛設置成 ：" + str);
                transformer.setType(str);
                TimeUnit.SECONDS.sleep(2);

                String type = transformer.getType();

                System.out.println(Thread.currentThread().getName()
                        + ": 獲取到的變形金剛是：" + type);

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

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

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?Transformer.java

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


/*
 * 每個線程都有且僅有一個 該類對象的引用。
 * 不應該在外部類中隨便的去new 所以構造方法私有
 * 
 */
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;
    }
    
    
}

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Transformer2.java(使用ThreadLocal類)

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


/*
 * 每個線程都有且僅有一個 該類對象的引用。
 * 
 */
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;
    }
}

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測試類:

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();
        }
    }
}

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