SynchronizedTest 4个线程 2个加一，2个减一

SynchronizedTest.java

package test;

public class SynchronizedTest {

    public static void main(String[] args) {
        J j = new J();
        Thread inc1 = new Thread(new IncrementThread(j), "inc1");
        Thread inc2 = new Thread(new IncrementThread(j), "inc2");
        Thread dec1 = new Thread(new DecrementThread(j), "dec1");
        Thread dec2 = new Thread(new DecrementThread(j), "dec2");
        inc1.start();
        inc2.start();
        dec1.start();
        dec2.start();
    }
}

class J {
    private int j;
    
    public synchronized void inc() {
        j++;
        System.out.println(Thread.currentThread().getName() + "=== after add ,j is " + j);
    }
    
    public synchronized void dec() {
        j--;
        System.out.println(Thread.currentThread().getName() + "=== after dec ,j is " + j);
    }
    
    
}


class IncrementThread implements Runnable {

    private J j;
    public IncrementThread(J j) {
        this.j = j;
    }
    
    
    @Override
    public void run() {
        j.inc();
    }
    
}

class DecrementThread implements Runnable {
    
    private J j;
    public DecrementThread(J j) {
        this.j = j;
    }
    
    @Override
    public void run() {
        j.dec();
    }
    
}


class AA {
    public synchronized void method1(){
        
    }
}


class B extends AA{

    @Override
    public synchronized void method1() {
        // synchronized关键字是不能继承的 必须显示定义
    }
    
}