读后感Java多线程编程核心技术十二

类ThreadLocal的使用

主要解决的是每个线程绑定自己的值，可以将ThreadLocal类比喻成全局存放数据的盒子，盒子中可以存储每个线程私有数据。

类ThreadLocal解决的是变量在不同线程间的隔离线，也就是不同线程拥有自己的值，不同线程中的值是可以放入ThreadLocal类中进行保存的
方法get()与null
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package Third;

public class Run {
public static ThreadLocal tl = new ThreadLocal();

public static void main(String[] args) {
    if (tl.get() == null) {
        System.out.println("从未放过值");
        tl.set("我的值");
    }
    System.out.println(tl.get());
    System.out.println(tl.get());
}

}

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验证线程变量的隔离性
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package Third;

public class ThreadA extends Thread {

@Override
public void run() {
    try {
        for (int i = 0; i < 100; i++) {
            if (Tools.tl.get() == null) {
                Tools.tl.set("ThreadA" + (i + 1));
            } else {
                System.out.println("ThreadA get Value=" + Tools.tl.get());
            }
            Thread.sleep(200);
        }
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

}

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package Third;

public class ThreadB extends Thread {

@Override
public void run() {
    try {
        for (int i = 0; i < 100; i++) {
            if (Tools.tl.get() == null) {
                Tools.tl.set("ThreadB" + (i + 1));
            } else {
                System.out.println("ThreadB get Value=" + Tools.tl.get());
            }
            Thread.sleep(200);
        }
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

}

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package Third;

public class Tools {

public static ThreadLocal tl = new ThreadLocal();

}

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package Third;

public class Run {

public static void main(String[] args) {

    try {
        ThreadA a = new ThreadA();
        ThreadB b = new ThreadB();
        a.start();
        b.start();

        for (int i = 0; i < 100; i++) {
            if (Tools.tl.get() == null) {
                Tools.tl.set("Main" + (i + 1));
            } else {
                System.out.println("Main get Value=" + Tools.tl.get());
            }
            Thread.sleep(200);
        }
    } catch (InterruptedException e) {
        e.printStackTrace();
    }

}

}

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每个线程取出自己的数据
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package Third;

import java.util.Date;

public class ThreadA extends Thread {

@Override
public void run() {
    try {
        for (int i = 0; i < 20; i++) {
            if (Tools.tl.get() == null) {
                Tools.tl.set(new Date());
            }
            System.out.println("A " + Tools.tl.get().getTime());
            Thread.sleep(100);
        }
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

}

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package Third;

import java.util.Date;

public class ThreadB extends Thread {

@Override
public void run() {
    try {
        for (int i = 0; i < 20; i++) {
            if (Tools.tl.get() == null) {
                Tools.tl.set(new Date());
            }
            System.out.println("B " + Tools.tl.get().getTime());
            Thread.sleep(100);
        }
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

}

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package Third;

import java.util.Date;

public class Tools {

public static ThreadLocal tl = new ThreadLocal();

}

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package Third;

public class Run {

public static void main(String[] args) {
    try {
        ThreadA a = new ThreadA();
        a.start();

        Thread.sleep(1000);

        ThreadB b = new ThreadB();
        b.start();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }

}

}
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此案例仅仅证明main线程有自己的值，那其他线程呢？
再次验证线程变量的隔离性

package Third;

public class Tools {
public static ThreadLocalExt tl = new ThreadLocalExt();
}

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package Third;

import java.util.Date;

public class ThreadLocalExt extends ThreadLocal {br/>@Override
protected Object initialValue() {
return new Date().getTime();
}
}

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package Third;

public class ThreadA extends Thread {

@Override
public void run() {
    try {
        for (int i = 0; i < 10; i++) {
            System.out.println("在ThreadA线程中取值=" + Tools.tl.get());
            Thread.sleep(100);
        }
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

}

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package Third;

public class Run {

public static void main(String[] args) {
    try {
        for (int i = 0; i < 10; i++) {
            System.out.println("       在Main线程中取值=" + Tools.tl.get());
            Thread.sleep(100);
        }
        Thread.sleep(5000);
        ThreadA a = new ThreadA();
        a.start();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

}

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