java中的synchronized

1、synchronized为互斥。该关键词可以申明方法也可以申明代码库。

import java.util.concurrent.TimeUnit;public class SynchronizedDemo1 {public synchronized static void synchronizedDemo(){try {TimeUnit.SECONDS.sleep(2);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("test1");}public static void test1(){Thread thread = new Thread(){public void run() {synchronizedDemo();}};thread.start();}public static void test2(){Thread thread = new Thread(){public void run() {synchronizedDemo();}};thread.start();}public static void main(String[] args) {SynchronizedDemo1 sd = new SynchronizedDemo1();sd.test1();SynchronizedDemo1 sd1 = new SynchronizedDemo1();sd1.test2();}}

该类中main为一个线程，分别调用同一个方法。结果得到的互斥的效果，必须要等待前一个方法执行完毕，才能执行后面的调用。经过测试，，只要是不同的线程，都会起到互斥的效果

2、下面再看一个例子没有static来修饰的，这里同一对象多个线程都能启动互斥的效果，如果是不同的对象就不能起到互斥的效果。

import java.util.concurrent.TimeUnit;public class SynchronizedDemo2 {public synchronized void synchronizedDemo(){try {TimeUnit.SECONDS.sleep(2);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("test1");}public void test1(){Thread thread = new Thread(){public void run() {synchronizedDemo();}};thread.start();}public void test2(){Thread thread = new Thread(){public void run() {synchronizedDemo();}};thread.start();}public static void main(String[] args) {SynchronizedDemo2 sd = new SynchronizedDemo2();sd.test1();SynchronizedDemo2 sd1 = new SynchronizedDemo2();sd1.test2();}}

3、将synchronized修饰在i代码块中。这里的效果和前面类似，只是将synchronized放在代码块中更加灵活。

public class SynchronizedDemo3 {public void synchronizedDemo(){System.out.println("进入方法：1");synchronized(this) {try {TimeUnit.SECONDS.sleep(2);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("等待后：2");}System.out.println("结束后：3");}public void test1(){Thread thread = new Thread(){public void run() {synchronizedDemo();}};thread.start();}public void test2(){Thread thread = new Thread(){public void run() {synchronizedDemo();}};thread.start();}public static void main(String[] args) {SynchronizedDemo3 sd = new SynchronizedDemo3();sd.test1();//SynchronizedDemo3 sd1 = new SynchronizedDemo3();sd.test2();}}<p>结果如下</p><p>进入方法：1</p><p>进入方法：1</p><p>等待后：2</p><p>结束后：3</p><p>等待后：2</p><p>结束后：3</p>

也许叔本华是对的，人与人的距离太远会寂寞到寒冷，