Java 学习笔记之 实例变量与线程安全

实例变量与线程安全：

不共享数据：

public class NoSharedThread extends Thread {
    private int count = 5;

    public NoSharedThread(String name){
        super();
        this.setName(name);
    }

    @Override
    public void run() {
        super.run();
        while (count > 0){
            count--;
            System.out.println("Thread name: " + Thread.currentThread().getName() + ", count: " + count);
        }
    }
}

public class ThreadRunMain {
    public static void main(String[] args) {
        testSharedSafeThead();
    }

    public static void testNoSharedThread() {
        NoSharedThread a = new NoSharedThread("a");
        NoSharedThread b = new NoSharedThread("b");
        NoSharedThread c = new NoSharedThread("c");
        a.start();
        b.start();
        c.start();
    }

}

运行结果：

可见线程之间没有互相干扰，都在操作自己的count变量。

共享数据：

public class SharedThread extends Thread{
    private int count = 5;
    public SharedThread(String name) {
        super();
        this.setName(name);
    }

    @Override
    public void run() {
        super.run();
        count--;
        System.out.println("Thread name: " + Thread.currentThread().getName() + ", count: " + count);
    }
}

public class ThreadRunMain {
    public static void main(String[] args) {
        testSharedThead();

    }

public static void testSharedThead(){
        SharedThread st = new SharedThread("SharedThread");
        Thread a = new Thread(st,"a");
        Thread b = new Thread(st,"b");
        Thread c = new Thread(st,"c");
        Thread d = new Thread(st,"d");
        Thread e = new Thread(st,"e");
        a.start();
        b.start();
        c.start();
        d.start();
        e.start();

}

}

运行结果：

可见线程之间互相干扰，产生count值一样的情况，非线程安全的问题出现。

共享数据线程安全：

public class SharedSafeThread extends Thread{
    private int count = 5;
    public SharedSafeThread(String name) {
        super();
        this.setName(name);
    }

    @Override
    public synchronized void run() {
        super.run();
        count--;
        System.out.println("Thread name: " + Thread.currentThread().getName() + ", count: " + count);
    }

}

public class ThreadRunMain {
    public static void main(String[] args) {
        testSharedSafeThead();
    }

    public static void testSharedSafeThead(){
        SharedSafeThread sst = new    SharedSafeThread("SharedSafeThread");
        Thread a = new Thread(sst,"a");
        Thread b = new Thread(sst,"b");
        Thread c = new Thread(sst,"c");
        Thread d = new Thread(sst,"d");
        Thread e = new Thread(sst,"e");
        a.start();
        b.start();
        c.start();
        d.start();
        e.start();

    }

}

运行结果：

可见线程之间没有互相干扰，count值没有重复，线程安全。