关键字synchronized还可以应用在static静态方法上，这样写那是对当前的*.java文件对应的class类进行持锁，
测试如下
package com.cky.bean;/**
* Created by edison on 2017/12/8.
*/
public class Service { synchronized public static void printA() {
try {
System.out.println("printA ThreadName"+Thread.currentThread().getName()+ "begin");
Thread.sleep(2000);
System.out.println("printA ThreadName"+Thread.currentThread().getName()+ "end");
} catch (InterruptedException e) {
e.printStackTrace();
}
} synchronized public static void printB(){
System.out.println("printb ThreadName"+Thread.currentThread().getName()+ "begin");
System.out.println("printb ThreadName"+Thread.currentThread().getName()+ "end"); }}
package com.cky.thread;import com.cky.bean.Service;/**
* Created by edison on 2017/12/8.
*/
public class ThreadA extends Thread{ @Override
public void run() {
super.run();
Service.printA();
}
}
package com.cky.thread;import com.cky.bean.Service;/**
* Created by edison on 2017/12/8.
*/
public class ThreadB extends Thread{ @Override
public void run() {
super.run();
Service.printB();
}
}
package com.cky.test;import com.cky.bean.Service;
import com.cky.thread.ThreadA;
import com.cky.thread.ThreadB;/**
* Created by edison on 2017/12/8.
*/
public class Test {
public static void main(String[] args) {
Service service = new Service();
ThreadA threadA = new ThreadA();
threadA.setName("a");
threadA.start();
ThreadB threadB = new ThreadB();
threadB.setName("b");
threadB.start();
}
}
printA ThreadNameabegin
printA ThreadNameaend
printb ThreadNamebbegin
printb ThreadNamebendProcess finished with exit code 0
程序运行结果：
同步的效果，和将synchronized关键字加到非static方法上使用的效果一致，但还是存在本质上的区别，synchronized加到static静态方法上时给Class类上锁，而加到非static静态方法上是给对象上锁。
为了验证不是同一个锁，测试如下。
package com.cky.bean;/**
* Created by edison on 2017/12/8.
*/
public class Service { synchronized public static void printA() {
try {
System.out.println("printA ThreadName"+Thread.currentThread().getName()+ "begin");
Thread.sleep(2000);
System.out.println("printA ThreadName"+Thread.currentThread().getName()+ "end");
} catch (InterruptedException e) {
e.printStackTrace();
}
} synchronized public static void printB(){
System.out.println("printb ThreadName"+Thread.currentThread().getName()+ "begin");
System.out.println("printb ThreadName"+Thread.currentThread().getName()+ "end"); } synchronized public void printC(){
System.out.println("printc ThreadName"+Thread.currentThread().getName()+ "begin");
System.out.println("printc ThreadName"+Thread.currentThread().getName()+ "end"); }}
package com.cky.thread;import com.cky.bean.Service;/**
* Created by edison on 2017/12/8.
*/
public class ThreadA extends Thread{ @Override
public void run() {
super.run();
Service.printA();
}
}
package com.cky.thread;import com.cky.bean.Service;/**
* Created by edison on 2017/12/8.
*/
public class ThreadB extends Thread{ @Override
public void run() {
super.run();
Service.printB();
}
}
package com.cky.thread;import com.cky.bean.Service;/**
* Created by edison on 2017/12/8.
*/
public class ThreadC extends Thread{ private Service service; public ThreadC(Service service) {
this.service = service;
} @Override
public void run() {
super.run();
service.printC();
}
}
package com.cky.test;import com.cky.bean.Service;
import com.cky.thread.ThreadA;
import com.cky.thread.ThreadB;
import com.cky.thread.ThreadC;/**
* Created by edison on 2017/12/8.
*/
public class Test {
public static void main(String[] args) {
Service service = new Service();
ThreadA threadA = new ThreadA();
threadA.setName("a");
threadA.start();
ThreadB threadB = new ThreadB();
threadB.setName("b");
threadB.start();
ThreadC threadC = new ThreadC(service);
threadC.setName("c");
threadC.start();
}
}
C:\itsoft\jdk\bin\java -Didea.launcher.port=7532 "-Didea.launcher.bin.path=C:\itsoft\idea\IntelliJ IDEA 2016.3.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\itsoft\jdk\jre\lib\charsets.jar;C:\itsoft\jdk\jre\lib\deploy.jar;C:\itsoft\jdk\jre\lib\ext\access-bridge-32.jar;C:\itsoft\jdk\jre\lib\ext\cldrdata.jar;C:\itsoft\jdk\jre\lib\ext\dnsns.jar;C:\itsoft\jdk\jre\lib\ext\jaccess.jar;C:\itsoft\jdk\jre\lib\ext\jfxrt.jar;C:\itsoft\jdk\jre\lib\ext\localedata.jar;C:\itsoft\jdk\jre\lib\ext\nashorn.jar;C:\itsoft\jdk\jre\lib\ext\sunec.jar;C:\itsoft\jdk\jre\lib\ext\sunjce_provider.jar;C:\itsoft\jdk\jre\lib\ext\sunmscapi.jar;C:\itsoft\jdk\jre\lib\ext\sunpkcs11.jar;C:\itsoft\jdk\jre\lib\ext\zipfs.jar;C:\itsoft\jdk\jre\lib\javaws.jar;C:\itsoft\jdk\jre\lib\jce.jar;C:\itsoft\jdk\jre\lib\jfr.jar;C:\itsoft\jdk\jre\lib\jfxswt.jar;C:\itsoft\jdk\jre\lib\jsse.jar;C:\itsoft\jdk\jre\lib\management-agent.jar;C:\itsoft\jdk\jre\lib\plugin.jar;C:\itsoft\jdk\jre\lib\resources.jar;C:\itsoft\jdk\jre\lib\rt.jar;C:\多线程核心技术\第一章\out\production\第一章;C:\itsoft\idea\IntelliJ IDEA 2016.3.3\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain com.cky.test.Test
printA ThreadNameabegin
printc ThreadNamecbegin
printc ThreadNamecend
printA ThreadNameaend
printb ThreadNamebbegin
printb ThreadNamebend
结果可见：
a和b和c是异步执行的，而不是按顺序执行的，因为一个是对象锁，一个是class锁，而class锁可以对所有的实例起作用
测试如下
package com.cky.bean;/**
* Created by edison on 2017/12/8.
*/
public class Service { synchronized public static void printA() {
try {
System.out.println("printA ThreadName"+Thread.currentThread().getName()+ "begin");
Thread.sleep(2000);
System.out.println("printA ThreadName"+Thread.currentThread().getName()+ "end");
} catch (InterruptedException e) {
e.printStackTrace();
}
} synchronized public static void printB(){
System.out.println("printb ThreadName"+Thread.currentThread().getName()+ "begin");
System.out.println("printb ThreadName"+Thread.currentThread().getName()+ "end"); }}
package com.cky.thread;import com.cky.bean.Service;/**
* Created by edison on 2017/12/8.
*/
public class ThreadA extends Thread{
private Service service; public ThreadA(Service service) {
this.service = service;
} @Override
public void run() {
super.run();
service.printA();
}
}
package com.cky.thread;import com.cky.bean.Service;/**
* Created by edison on 2017/12/8.
*/
public class ThreadB extends Thread{ private Service service; public ThreadB(Service service) {
this.service = service;
} @Override
public void run() {
super.run();
service.printB();
}
}
package com.cky.test;import com.cky.bean.Service;
import com.cky.thread.ThreadA;
import com.cky.thread.ThreadB;/**
* Created by edison on 2017/12/8.
*/
public class Test {
public static void main(String[] args) {
Service service1 = new Service();
Service service2 = new Service();
ThreadA threadA = new ThreadA(service1);
threadA.setName("a");
threadA.start();
ThreadB threadB = new ThreadB(service2);
threadB.setName("b");
threadB.start(); }
}
printA ThreadNameabegin
printA ThreadNameaend
printb ThreadNamebbegin
printb ThreadNamebend
同步synchronized（class）代码块的作用和synchronized static 方法一样，
测试如下修改Service类如下
package com.cky.bean;/**
* Created by edison on 2017/12/8.
*/
public class Service { public static void printA() {
try {
synchronized (Service.class) {
System.out.println("printA ThreadName"+Thread.currentThread().getName()+ "begin");
Thread.sleep(2000);
System.out.println("printA ThreadName"+Thread.currentThread().getName()+ "end");
} } catch (InterruptedException e) {
e.printStackTrace();
}
} public static void printB(){
synchronized(Service.class) {
System.out.println("printb ThreadName"+Thread.currentThread().getName()+ "begin");
System.out.println("printb ThreadName"+Thread.currentThread().getName()+ "end");
} }}
printA ThreadNameabegin
printA ThreadNameaend
printb ThreadNamebbegin
printb ThreadNamebend
