使用synchronized的注意点

  在http://blog.youkuaiyun.com/xyc_csdn/article/details/78155932这篇博客中详细讲了一下synchronized关键字的使用方法。在这里补充几个使用synchronized时需要注意的点。

先看代码

• ObjectLock.java

package com.xiayc.sync;

public class ObjectLock {
    private String name;

    public ObjectLock(String name) {
        super();
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

• ConstantSynchronized.java

package com.xiayc.sync;

public class ConstantSynchronized {
    private Long id;
    private String name;
    private String stringLock = "LOCK";
    private Integer integerLock = 1;
    private double doubleLock = 1D;
    private ObjectLock objectLock = new ObjectLock("objectLock");

    public ConstantSynchronized(Long id, String name) {
        super();
        this.id = id;
        this.name = name;
    }

    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getName() {
        synchronized (this.objectLock) {
            return name;
        }
    }
    public void setName(String name) {
        synchronized (this.objectLock) {
            try {
//              this.stringLock="hhh";
//              this.integerLock=2;
                this.objectLock.setName("hhh");
                Thread.sleep(3000);
                this.name = name;
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        ConstantSynchronized constantSynchronized = new ConstantSynchronized(1L,"任务1");
        new Thread(new Runnable() {
            @Override
            public void run() {
                constantSynchronized.setId(2L);
                constantSynchronized.setName("任务2");
            }
        }, "t1").start();

        new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("id:"+constantSynchronized.getId());
                System.out.println("name:"+constantSynchronized.getName());
            }
        }, "t2").start();
    }
}

总结

• synchronized关键字不能修饰int、double等基本数据类型；

• synchronized关键字最好不要修饰String、Integer等基本数据对象类型，因为如果基本数据对象类型的值发生改变的话，原先加的锁可能会丢失；

• synchronized关键字修饰对象时，如果对象的属性值发生改变（对象本身发生改变例外）不会影响锁的稳定；

后续：https://blog.youkuaiyun.com/xyc_csdn/article/details/79920120