//没有互斥锁的情况(可以自己跑跑看运行结果): public class LockDemo { // private static Object lock = new Object(); // static确保只有一把锁 private int i = 0 ; public void increaseI() { // synchronized (lock) { for ( int k= 0 ;k< 10 ;k++) { // 对i执行10次增1操作 i++; } System.out.println(Thread.currentThread().getName() + "线程,i现在的值:" + i); // } } public static void main(String[] args) { LockDemo ld = new LockDemo(); int threadNum = 1000 ; // 选择1000个线程让结果更加容易观测到 MyThread[] threads = new MyThread[threadNum]; for ( int i= 0 ;i<threads.length;i++) { threads[i] = new MyThread(ld); // 所有线程共用一个LockDemo对象 threads[i].start(); } } } class MyThread extends Thread { LockDemo ld; public MyThread(LockDemo ld) { this .ld = ld; } public void run() { ld.increaseI(); } } //加上互斥锁以后: public class LockDemo { private static Object lock = new Object(); // static确保只有一把锁 private int i = 0 ; public void increaseI() { synchronized (lock) { for ( int k= 0 ;k< 10 ;k++) { // 对i执行10次增1操作 i++; } System.out.println(Thread.currentThread().getName() + "线程,i现在的值:" + i); } } public static void main(String[] args) { LockDemo ld = new LockDemo(); int threadNum = 1000 ; // 选择1000个线程让结果更加容易观测到 MyThread[] threads = new MyThread[threadNum]; for ( int i= 0 ;i<threads.length;i++) { threads[i] = new MyThread(ld); // 所有线程共用一个LockDemo对象 threads[i].start(); } } } class MyThread extends Thread { LockDemo ld; public MyThread(LockDemo ld) { this .ld = ld; } public void run() { ld.increaseI(); } } |