两个线程交替打印

public class ThreadTest {
    volatile int flag=0;

    public static void main(String[] args) throws InterruptedException {
        ThreadTest threadTest = new ThreadTest();
        threadTest.runThread();

    }

    public void runThread() throws InterruptedException{
        Thread t1=new Thread(new Thread1());
        Thread t2=new Thread(new Thread2());
        t1.start();
        t2.start();
    }
    public class Thread1 implements Runnable{

        public void run() {
            int i=1;
            while(i<=100){
                if(flag==0)
                {
                    System.out.println("线程1 " + i);
                    i+=2;
                    flag=1;
                }
            }
        }

    }

    public class Thread2 implements Runnable{

        public void run() {
            int i=2;
            while(i<=100){
                if(flag==1)
                {
                    System.out.println("线程2 " + i);
                    i+=2;
                    flag=0;
                }
            }
        }

    }
}

// 模仿大佬的
public class ThreadTest {
    int i =1;
    boolean firstDone = false;
    Object lock = new Object();
    public static void main(String[] args) {
        ThreadTest t =new ThreadTest();
        t.print();
    }
    void print(){
        Thread t1 = new Thread(new Runnable() {
            public void run() {
                for(;i<=100;)
                {
                    synchronized (lock) {
                        if(!firstDone) {
                            System.out.println(Thread.currentThread().getName());
                            System.out.println(i++);
                            firstDone = true;
                            lock.notify();
                        }
                        else{
                            try {
                                lock.wait();
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }
        });
        Thread t2 = new Thread(new Runnable() {
            public void run() {
                for(;i<=100;)
                {
                    synchronized (lock) {
                        if(firstDone) {
                            System.out.println(Thread.currentThread().getName());
                            System.out.println(i++);
                            firstDone = false;
                            lock.notify();
                        }
                        else {
                            try {
                                lock.wait();
                            } catch (InterruptedException e) {
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }
        });
        t1.start();
        t2.start();
    }
}