synchronized用法

一、修饰方法

1.修饰普通方法　

　　① synchronized方法 VS 非synchronized方法

public void method() {
    System.out.println("run       method");
    try {
        Thread.sleep(2000);
    } catch (InterruptedException e) {
    }
    System.out.println("end       method");
}

public synchronized void generalMethod() {
    System.out.println("run       general");
    try {
        Thread.sleep(5000);
    } catch (InterruptedException e) {
    }
    System.out.println("end       general");
}
运行结果：
run       method
run       general
end       method
end       general

View Code

　　小结：synchronized修饰的方法与其它非synchronized修饰的方法同时调用不相互影响

2.修饰静态方法

　　① 静态synchronized方法 VS synchronized方法

public synchronized void generalMethod() {
    System.out.println("run       general");
    try {
        Thread.sleep(5000);
    } catch (InterruptedException e) {
    }
    System.out.println("end       general");
}

public synchronized static void staticMethod() {
    System.out.println("run       static");
    try {
        Thread.sleep(5000);
    } catch (InterruptedException e) {
    }
    System.out.println("end       static");
}
运行结果：
run       general
run       static
end       general
end       static

View Code

　　小结：静态synchronized方法与synchronized方法同时调用不会阻塞

二、修饰代码块

1.同步对象为class

　　① 同步对象为class VS 同步对象为对象

public void objectMethod() {
    synchronized (this) {
        System.out.println("run       object");
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
        }
        System.out.println("end       object");
    }
}


public void classMethod() {
    synchronized (SynchronizedTest.class) {
        System.out.println("run       class");
    }
    try {
        Thread.sleep(5000);
    } catch (InterruptedException e) {
    }
    System.out.println("end       class");
}
运行结果：
run       object
run       class
end       class
end       object

View Code

　　小结：调用同步对象为class代码块与调用同步对象为对象的代码块不会阻塞

　　② 同步对象为class VS 静态synchronized方法

public synchronized static void staticMethod() {
    System.out.println("run       static");
    try {
        Thread.sleep(5000);
    } catch (InterruptedException e) {
    }
    System.out.println("end       static");
}    
public void classMethod() {
    synchronized (SynchronizedTest.class) {
        System.out.println("run       class");
    }
    try {
        Thread.sleep(5000);
    } catch (InterruptedException e) {
    }
    System.out.println("end       class");
}
运行结果：
run       static
end       static
run       class
end       class

View Code

　　小结：调用同步对象为class代码块与静态synchronized方法同时调用会阻塞

2.同步对象为对象

　　① 同步对象为class VS 同步对象为对象

public void classMethod() {
    synchronized (SynchronizedTest.class) {
        System.out.println("run       class");
    }
    try {
        Thread.sleep(5000);
    } catch (InterruptedException e) {
    }
    System.out.println("end       class");
}

public void objectMethod() {
    synchronized (this) {
        System.out.println("run       object");
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
        }
        System.out.println("end       object");
    }
}
运行结果：
run       class
run       object
end       class
end       object

View Code

结论：

　　静态方法属于类，同步静态方法的锁是加在类上；普通方法属于对象，同步非静态方法的锁是加在那个对象上；锁的对象不一样就不会阻塞，代码块同理。

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