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。