2.2.7锁定非this对象synchronized(this)

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package cha02.execise17;/** * Created by sunyifeng on 17/9/25. */public class Service {    private String usernameParam;    private String passwordParam;    private String anyString = new String();    public void setPasswordParam(String usernameParam, String passwordParam){        try{            synchronized (anyString){                System.out.println("进入线程名称为：" + Thread.currentThread().getName());                this.usernameParam = usernameParam;                Thread.sleep(3000);                this.passwordParam = passwordParam;                System.out.println("离开线程名称为：" + Thread.currentThread().getName());            }        }catch (InterruptedException e){            e.printStackTrace();        }    }}

package cha02.execise17;/** * Created by sunyifeng on 17/9/25. */public class ThreadA extends Thread {    private Service service;    public ThreadA(Service service) {        super();        this.service = service;    }    @Override    public void run() {        service.setPasswordParam("a", "aa");    }}

package cha02.execise17;/** * Created by sunyifeng on 17/9/25. */public class ThreadB extends Thread {    private Service service;    public ThreadB(Service service) {        super();        this.service = service;    }    @Override    public void run() {        service.setPasswordParam("b", "bb");    }}

package cha02.execise17;/** * Created by sunyifeng on 17/9/25. */public class Run {    public static void main(String[] args) {        Service service = new Service();        // 线程A        ThreadA threadA = new ThreadA(service);        threadA.setName("A");        threadA.start();        // 线程B        ThreadB threadB = new ThreadB(service);        threadB.setName("B");        threadB.start();    }}

运行结果：

进入线程名称为：A
离开线程名称为：A
进入线程名称为：B
离开线程名称为：B

程序分析：

如果类中有多个同步方法，这时虽然能实现同步，但会受到影响，如果使用非this对象，则可以实现异步，提高运行效率。

更改以上代码如下：

package cha02.execise17;/** * Created by sunyifeng on 17/9/25. */public class Service {    private String usernameParam;    private String passwordParam;    public void setPasswordParam(String usernameParam, String passwordParam){        try{            String anyString = new String(); // FIXME: 注意这里            synchronized (anyString){                System.out.println("进入线程名称为：" + Thread.currentThread().getName());                this.usernameParam = usernameParam;                Thread.sleep(3000);                this.passwordParam = passwordParam;                System.out.println("离开线程名称为：" + Thread.currentThread().getName());            }        }catch (InterruptedException e){            e.printStackTrace();        }    }}

运行结果如下：

进入线程名称为：A
进入线程名称为：B
离开线程名称为：A
离开线程名称为：B

程序分析：

使用synchronized(非this)锁，对象监视器必须是同一个对象。以上anyString放在方法内部创建，线程每次进来都是不同对象。

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