synchronized三種使用方式，及鎖的類型驗證

Synchronized常用三種使用方式

1、修飾普通方法：鎖對象即為當前對象

2、修飾靜態方法：鎖對象為當前Class對象

3、修飾代碼塊：鎖對象為synchronized緊接着的小括號內的對象

一、驗證修飾普通方法時鎖對象

package com.demo;

public class ThreadTest {

    public static void main(String[] args) {
        Thread t1 = new MyThread1();
        Thread t2 = new MyThread2(t1);

        t1.start();// 默認priority=5
        t2.start();

        t2.setPriority(9);

        System.out.println("線程1：" + t1.getState());
        System.out.println("線程2：" + t2.getState());
    }

}

class MyThread1 extends Thread {

    @Override
    public void run() {
        dosome();
    }

    public synchronized void dosome() {
        System.out.println("mythread1");
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("sleep end");
    }
}

class MyThread2 extends Thread {
    private Object lock;

    public MyThread2(Object lock) {
        this.lock = lock;
    }

    @Override
    public void run() {
        synchronized (lock) {
            System.out.println("mythread2");
        }
    }

}

現象：先逐行輸出mythread1，線程1：RUNNABLE，線程2：BLOCKED，之后暫停五分鍾，逐行輸出sleep end，mythread2

分析：線程2與線程1擁有相同的鎖，線程1優先級高於線程2，線程1優先執行，獲取到鎖，執行sleep，未釋放鎖，線程2未獲取到鎖，處於阻塞狀態，線程1sleep結束，輸出sleep end，並釋放鎖，線程2獲取到鎖，執行輸出mythread2

結論：當synchronized修飾普通方法時，鎖對象即為當前對象

二、驗證修飾靜態方法時鎖對象

對上述代碼稍作修改，在dosome方法上添加static關鍵字，main方法中，線程2對象初始化時，傳入MyThread1.class

現象：與上述現象一致

分析：同上

結論：當synchronized修飾靜態方法時，鎖對象為當前Class對象

三、驗證修飾代碼塊時鎖對象

package com.demo;

public class ThreadTest {

    public static void main(String[] args) {
        Object o = new Object();

        Thread t1 = new MyThread1(o);
        Thread t2 = new MyThread2(o);

        t1.start();
        t2.start();

        t2.setPriority(9);
        System.out.println("線程1：" + t1.getState());
        System.out.println("線程2：" + t2.getState());

    }

}

class MyThread1 extends Thread {
    private Object lock;

    public MyThread1(Object lock) {
        this.lock = lock;
    }

    @Override
    public void run() {

        synchronized (lock) {
            System.out.println("mythread1");
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("sleep end");
        }
    }

}

class MyThread2 extends Thread {
    private Object lock;

    public MyThread2(Object lock) {
        this.lock = lock;
    }

    @Override
    public void run() {
        synchronized (lock) {
            System.out.println("mythread2");
        }
    }

}

現象：同上

分析：同上

結論：當使用synchronized修改代碼塊時，其后小括號中的對象即為對象鎖。