Java 学习笔记之 Synchronized锁对象

Synchronized锁对象：

Synchronized取得的锁都是对象锁，而不是把一段代码或方法当作锁，哪个线程执行带synchronized关键字的方法，哪个线程就持有该方法所属对象的锁，那么其他线程只能等待，前提是多个线程访问的是同一个对象。

实验得出以下结论：

• A线程先持有object对象的Lock锁，B线程可以以异步的方式调用object对象中的非synchronized类型的方法。

public class Sync1Object {
    synchronized public void methodA() {
        try {
            System.out.println("begin methodA threadName = "
                    + Thread.currentThread().getName());
            Thread.sleep(5000);
            System.out.println("A end endTime = " + System.currentTimeMillis());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

     public void methodB() {
        try {
            System.out.println("begin methodB threadName = "
                    + Thread.currentThread().getName() + " begin time = "
                    + System.currentTimeMillis());
            Thread.sleep(3000);
            System.out.println("B end");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

public class Sync1ThreadA extends Thread{
    private Sync1Object object;

    public Sync1ThreadA(Sync1Object object) {
        this.object = object;
    }

    @Override
    public void run() {
        super.run();
        object.methodA();
    }
}

public class Sync1ThreadB extends Thread{
    private Sync1Object object;

    public Sync1ThreadB(Sync1Object object) {
        this.object = object;
    }

    @Override
    public void run() {
        super.run();
        object.methodB();
    }
}

public class ThreadRunMain {
    public static void main(String[] args) {
        testSync1Thread();
    }

    public static void testSync1Thread(){
        try {
            Sync1Object object = new Sync1Object();
            Sync1ThreadA a = new Sync1ThreadA(object);
            a.setName("A");
            a.start();
            Thread.sleep(100);
            Sync1ThreadB b = new Sync1ThreadB(object);
            b.setName("B");
            b.start();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

运行结果：

• A线程先持有object对象的Lock锁，B线程如果在这个时候调用object对象中的synchronized类型的方法则需要等待，同步串行执行。

public class Sync1Object {
    synchronized public void methodA() {
        try {
            System.out.println("begin methodA threadName = "
                    + Thread.currentThread().getName());
            Thread.sleep(5000);
            System.out.println("A end endTime = " + System.currentTimeMillis());
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

     synchronized public void methodB() {
        try {
            System.out.println("begin methodB threadName = "
                    + Thread.currentThread().getName() + " begin time = "
                    + System.currentTimeMillis());
            Thread.sleep(3000);
            System.out.println("B end");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

public class Sync1ThreadA extends Thread{
    private Sync1Object object;

    public Sync1ThreadA(Sync1Object object) {
        this.object = object;
    }

    @Override
    public void run() {
        super.run();
        object.methodA();
    }
}

public class Sync1ThreadB extends Thread{
    private Sync1Object object;

    public Sync1ThreadB(Sync1Object object) {
        this.object = object;
    }

    @Override
    public void run() {
        super.run();
        object.methodB();
    }
}

public class ThreadRunMain {
    public static void main(String[] args) {
        testSync1Thread();
    }

    public static void testSync1Thread(){
        try {
            Sync1Object object = new Sync1Object();
            Sync1ThreadA a = new Sync1ThreadA(object);
            a.setName("A");
            a.start();
            Thread.sleep(100);
            Sync1ThreadB b = new Sync1ThreadB(object);
            b.setName("B");
            b.start();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

运行结果：