两线程交替打印数字

加锁实现

//两线程交替打印1-20
public class Main{
    public static void main(String[] args){
        Object lock=new Object();
        final int maxNum=20;
        new Thread(()->{
            for(int i=1;i<maxNum;i+=2){
                synchronized (lock){
                    System.out.print(i+" ");
                    lock.notify();
                    try {
                        if(i<maxNum-1){
                            lock.wait();
                        }
                    } catch (InterruptedException e) {}
                }
            }
        }).start();
        new Thread(()->{
            for(int i=2;i<=maxNum;i+=2){
                synchronized (lock){
                    System.out.print(i+" ");
                    lock.notify();
                    try {
                        if(i<maxNum){
                            lock.wait();
                        }
                    }catch (InterruptedException e){}
                }
            }
        }).start();
    }
}

无锁实现

//两线程交替打印1-20
public class Main{
    public volatile static boolean flag=true;
    public static void main(String[] args){
        final int maxNum=20;
        new Thread(()->{
            for(int i=1;i<maxNum;i+=2){
                while (!flag);
                if(flag){
                    System.out.print(i+" ");
                    flag=false;
                }
            }
        }).start();
        new Thread(()->{
            for(int i=2;i<=maxNum;i+=2){
                while (flag);
                if(!flag){
                    System.out.print(i+" ");
                    flag=true;
                }
            }
        }).start();
    }
}

最后对于while(flag);可以改写为while(flag) Thread.onSpinWait();代表flag==false时自旋。