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静态同步synchronized方法
package com.demo19;
public class MyObject {
synchronized public static void a(){
try {
System.out.println("线程：" + Thread.currentThread().getName() + " 开始时间：" + System.currentTimeMillis());
Thread.sleep(3000);
System.out.println("线程：" + Thread.currentThread().getName() + " 结束时间：" + System.currentTimeMillis());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
synchronized public static void b(){
System.out.println("线程：" + Thread.currentThread().getName() + " 开始时间：" + System.currentTimeMillis());
System.out.println("线程：" + Thread.currentThread().getName() + " 结束时间：" + System.currentTimeMillis());
}
}
package com.demo19;
public class ThreadA extends Thread {
@Override
public void run() {
MyObject.a();
}
}
package com.demo19;
public class ThreadB extends Thread {
@Override
public void run() {
MyObject.b();
}
}
package com.demo19;
public class run {
public static void main(String[] args) {
ThreadA threadA = new ThreadA();
ThreadB threadB = new ThreadB();
threadA.setName("A");
threadB.setName("B");
threadA.start();
threadB.start();
}
}
运行结果：
线程：A 开始时间：1544844475598
线程：A 结束时间：1544844478598
线程：B 开始时间：1544844478598
线程：B 结束时间：1544844478598看上去跟之前使用synchronized同步非静态方法的效果没什么区别，但本质上却是有区别的。synchronized同步静态方法，加在class上；synchronized同步非静态方法，是给对象上锁。
为了验证不是同一个锁，继续进行实验。
package com.demo19;
public class MyObject {
synchronized public static void a(){
try {
System.out.println("线程：" + Thread.currentThread().getName() + " 开始时间：" + System.currentTimeMillis());
Thread.sleep(3000);
System.out.println("线程：" + Thread.currentThread().getName() + " 结束时间：" + System.currentTimeMillis());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
synchronized public static void b(){
System.out.println("线程：" + Thread.currentThread().getName() + " 开始时间：" + System.currentTimeMillis());
System.out.println("线程：" + Thread.currentThread().getName() + " 结束时间：" + System.currentTimeMillis());
}
synchronized public void c(){
System.out.println("线程：" + Thread.currentThread().getName() + " 开始时间：" + System.currentTimeMillis());
System.out.println("线程：" + Thread.currentThread().getName() + " 结束时间：" + System.currentTimeMillis());
}
}
package com.demo19;
public class ThreadA extends Thread {
private MyObject myObject;
public ThreadA(MyObject myObject) {
this.myObject = myObject;
}
@Override
public void run() {
MyObject.a();
}
}
package com.demo19;
public class ThreadB extends Thread {
private MyObject myObject;
public ThreadB(MyObject myObject) {
this.myObject = myObject;
}
@Override
public void run() {
MyObject.b();
}
}
package com.demo19;
public class ThreadC extends Thread {
private MyObject myObject;
public ThreadC(MyObject myObject) {
this.myObject = myObject;
}
@Override
public void run(){
myObject.c();
}
}
package com.demo19;
public class run {
public static void main(String[] args) {
MyObject myObject = new MyObject();
ThreadA threadA = new ThreadA(myObject);
ThreadB threadB = new ThreadB(myObject);
ThreadC threadC = new ThreadC(myObject);
threadA.setName("A");
threadB.setName("B");
threadC.setName("C");
threadA.start();
threadB.start();
threadC.start();
}
}
运行结果：
线程：A 开始时间：1544845870678
线程：C 开始时间：1544845870679
线程：C 结束时间：1544845870679
线程：A 结束时间：1544845873678
线程：B 开始时间：1544845873678
线程：B 结束时间：1544845873678很明显 异步，原因是持有不同的锁。一个是对象锁，一个是class锁。class锁可以对类的所有实例对象起作用！
下面对该结论进行实验：
package com.demo19;
public class MyObject {
synchronized public static void a(){
try {
System.out.println("线程：" + Thread.currentThread().getName() + " 开始时间：" + System.currentTimeMillis());
Thread.sleep(3000);
System.out.println("线程：" + Thread.currentThread().getName() + " 结束时间：" + System.currentTimeMillis());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
synchronized public static void b(){
System.out.println("线程：" + Thread.currentThread().getName() + " 开始时间：" + System.currentTimeMillis());
System.out.println("线程：" + Thread.currentThread().getName() + " 结束时间：" + System.currentTimeMillis());
}
}
package com.demo19;
public class ThreadA extends Thread {
private MyObject myObject;
public ThreadA(MyObject myObject) {
this.myObject = myObject;
}
@Override
public void run() {
MyObject.a();
}
}
package com.demo19;
public class ThreadB extends Thread {
private MyObject myObject;
public ThreadB(MyObject myObject) {
this.myObject = myObject;
}
@Override
public void run() {
MyObject.b();
}
}
package com.demo19;
public class run {
public static void main(String[] args) {
MyObject myObject1 = new MyObject();
MyObject myObject2 = new MyObject();
ThreadA threadA = new ThreadA(myObject1);
ThreadB threadB = new ThreadB(myObject2);
threadA.setName("A");
threadB.setName("B");
threadA.start();
threadB.start();
}
}
运行结果：
线程：A 开始时间：1544846287092
线程：A 结束时间：1544846290092
线程：B 开始时间：1544846290092
线程：B 结束时间：1544846290092通过结论验证，class锁可以对类的所有对象实例起作用。
synchronized(class)同步代码块
package com.demo19;
public class MyObject {
public void a(){
synchronized (MyObject.class){
try {
System.out.println("线程：" + Thread.currentThread().getName() + " 开始时间：" + System.currentTimeMillis());
Thread.sleep(3000);
System.out.println("线程：" + Thread.currentThread().getName() + " 结束时间：" + System.currentTimeMillis());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public void b(){
synchronized(MyObject.class){
System.out.println("线程：" + Thread.currentThread().getName() + " 开始时间：" + System.currentTimeMillis());
System.out.println("线程：" + Thread.currentThread().getName() + " 结束时间：" + System.currentTimeMillis());
}
}
}
package com.demo19;
public class ThreadA extends Thread {
private MyObject myObject;
public ThreadA(MyObject myObject) {
this.myObject = myObject;
}
@Override
public void run() {
myObject.a();
}
}
package com.demo19;
public class ThreadB extends Thread {
private MyObject myObject;
public ThreadB(MyObject myObject) {
this.myObject = myObject;
}
@Override
public void run() {
myObject.b();
}
}
package com.demo19;
public class run {
public static void main(String[] args) {
MyObject myObject1 = new MyObject();
MyObject myObject2 = new MyObject();
ThreadA threadA = new ThreadA(myObject1);
ThreadB threadB = new ThreadB(myObject2);
threadA.setName("A");
threadB.setName("B");
threadA.start();
threadB.start();
}
}
运行结果：
线程：A 开始时间：1544846633091
线程：A 结束时间：1544846636092
线程：B 开始时间：1544846636092
线程：B 结束时间：1544846636092结论：synchronized(class)与同步静态方法的作用一样。