java中synchronized锁对象的具体理解

Love The Way You Lie 2022-04-11 06:48 249阅读 0赞

1.对于锁参数对象，只有参数对象是同一个对象时才会锁，不同的对象不会锁；

2.锁当前类对象，所有调用该类对象的情况下都会进行锁操作

总结的不好，可能理解不了，直接看代码和执行结果

锁参数对象：
    public class TestThread {
    
    	public static void main(String[] args) {
    		T2 t2 = new T2();
    		new T(t2,"lxl0").start();
    		new T(t2,"lxl0").start();
    		new T(t2,"lxl2").start();
    		new T(t2,"lxl3").start();
    	}
    }
    
    class T extends Thread {
    	T2 t2;
    	String userId;
    
    	public T(T2 t2,String userId){
    		this.t2 = t2;
    		this.userId = userId;
    	}
    	public void run() {
    		t2.m(userId);
    	}
    }
    
    class T2{
    	public void m(String userId) {
    		System.out.println("m................");
    		synchronized (userId) {
    			try {
    				System.out.println("userId:" + userId);
    				Thread.sleep(5000);
    			} catch (InterruptedException e) {
    				e.printStackTrace();
    			}
    		}
    	}
    }
    
    -----------------------------------------------
    执行结果：
    m................
    userId:lxl0
    m................
    m................
    userId:lxl2
    m................
    userId:lxl3
    userId:lxl0

2.锁类对象

锁类对象：
    public class TestThread {
    
    	public static void main(String[] args) {
    		T2 t2 = new T2();
    		new T(t2,"lxl0").start();
    		new T(t2,"lxl0").start();
    		new T(t2,"lxl2").start();
    		new T(t2,"lxl3").start();
    	}
    }
    
    class T extends Thread {
    	T2 t2;
    	String userId;
    
    	public T(T2 t2,String userId){
    		this.t2 = t2;
    		this.userId = userId;
    	}
    	public void run() {
    		t2.m(userId);
    	}
    }
    
    class T2{
    	public void m(String userId) {
    		System.out.println("m................");
    		synchronized (this) {
    			try {
    				System.out.println("userId:" + userId);
    				Thread.sleep(5000);
    			} catch (InterruptedException e) {
    				e.printStackTrace();
    			}
    		}
    	}
    }
    -----------------------------
    执行结果：
    m................
    userId:lxl0
    m................
    m................
    m................
    userId:lxl3
    userId:lxl2
    userId:lxl0