Java多线程交替打印

1. 双线程交替打印奇偶数

class Printer{
    private int num=1;  //要打印的数字
    private Object myLock = new Object();
    public static void main(String[] args){
        Printer p=new Printer();
        Thread t1=new Thread( ()->p.printNum(true), "threadA");
        t1.start();
        Thread t2=new Thread( ()->p.printNum(false), "threadB");
        t2.start();
    }
    private void printNum(boolean isOdd){
        while(num<10){  // 注意是小于，如果是等于，会卡死，不会主动退出
            synchronized (myLock){
                //不满足条件就阻塞 例如 isOdd=true，但num是偶数，阻塞
                while( (isOdd && num%2==0) || (!isOdd && num%2!=0)){  
                    try {
                        myLock.wait();
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                }
                if(num<=10){
                    System.out.println(Thread.currentThread().getName()+":"+num);
                    num++;
                    myLock.notifyAll();
                }
            }
        }
    }
}

2. 三线程交替打印1-10

class Printer{
    private int num=1;
    private Object myLock=new Object();
    public static void main(String[] args){
        Printer p=new Printer();
        Thread t1=new Thread( ()-> p.printNum(1), "threadA");
        t1.start();

        Thread t2=new Thread( ()-> p.printNum(2), "threadB");
        t2.start();

        Thread t3=new Thread( ()-> p.printNum(0), "threadC");
        t3.start();
    }

    void printNum(int need){
        while(num<10){  // 注意是小于
            synchronized (myLock) {
                while (num % 3 != need) {
                    try {
                        myLock.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                if(num<=10){
                    System.out.println(Thread.currentThread().getName()+":"+num);
                    num++;
                    myLock.notifyAll();
                }
            }
        }
    }
}

3. 三线程各打印1 2 3，分别打印5次

class Printer{
    private int condition=1;
    private Object myLock = new Object();
    public static void main(String[] args){
        Printer p = new Printer();
        Thread t1=new Thread( () -> p.printNum(1), "threadA");
        t1.start();
        Thread t2=new Thread( () -> p.printNum(2), "threadB");
        t2.start();
        Thread t3=new Thread( () -> p.printNum(3), "threadC");
        t3.start();
    }

    private void printNum(int need){
        for(int i=0;i<5;i++){
            synchronized (myLock){
                while(condition!=need){
                    try {
                        myLock.wait();
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                }
                System.out.println(Thread.currentThread().getName()+":"+need);
                condition=(condition%3)+1;
                myLock.notifyAll();
            }
        }
    }
}

4. 三个线程分别交替打印A B C，各5次

// 和上面一样，只是输出变一下
class Printer{
    private int condition=1;
    private Object myLock = new Object();
    public static void main(String[] args){
        Printer p = new Printer();
        Thread t1=new Thread( () -> p.printNum(1), "threadA");
        t1.start();
        Thread t2=new Thread( () -> p.printNum(2), "threadB");
        t2.start();
        Thread t3=new Thread( () -> p.printNum(3), "threadC");
        t3.start();
    }

    private void printNum(int need){
        for(int i=0;i<5;i++){
            synchronized (myLock){
                while(condition!=need){
                    try {
                        myLock.wait();
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                } 
			    System.out.printf("%s:%c\n",Thread.currentThread().getName(), need+64); // 这里利用ASCII码打印，方便一些 
                condition=(condition%3)+1;
                myLock.notifyAll();
            }
        }
    }
}