代码

import com.roocon.thread.t5.Singleton2;
//一个线程执行完后，更改状态，再执行下一个
public class Demo2 {
   
   private volatile int signal;
   
   public void set (int value) {
       this.signal = value;
   }
   
   public int get () {
       return signal;
   }
   
   public static void main(String[] args) {
       Demo2 d = new Demo2();
       new Thread(new Runnable() {
           
           @Override
           public void run() {
               synchronized (d) {
                   System.out.println("修改状态的线程执行...");
                   try {
                       Thread.sleep(5000);
                   } catch (InterruptedException e) {
                       e.printStackTrace();
                   }
                   d.set(1);
                   System.out.println("状态值修改成功。。。");
                   d.notify();
               }
           }
       }).start();
       
       
       new Thread(new Runnable() {
           
           @Override
           public void run() {
               synchronized (d) {
                   // 等待signal为1开始执行，否则不能执行
                   while(d.get() != 1) {
                       try {
                           d.wait();
                       } catch (InterruptedException e) {
                           e.printStackTrace();
                       }
                   }
                   // 当信号为1 的时候，执行代码
                   System.out.println("模拟代码的执行...");
               }
           }
       }).start();
   }

}

示例

public class Target1 implements Runnable {
    
    private Demo3 demo;
    
    public Target1(Demo3 demo) {
        this.demo = demo;
    }

    @Override
    public void run() {
        demo.set();
    }

}
public class Target2 implements Runnable {
    
    private Demo3 demo;

    public Target2(Demo3 demo) {
        this.demo = demo;
    }

    @Override
    public void run() {
        demo.get();
    }

}

import java.util.concurrent.TimeUnit;
/*
 * 1.wait,notify必须要在同步代码块执行，synchronized
 * 2.加对象d.wait()   d.notify()   见demo类
 * 3.调用wait会使线程失去锁（synchronized）
 * 4.notify执行后需要等锁释放才会唤醒别的线程
 */
        
public class Demo3 {

private volatile int signal;
    
    public synchronized void set () {
        signal = 1;
        notifyAll(); // notify方法会随机叫醒一个处于wait状态的线程
         // notifyAll叫醒所有的处于wait线程，争夺到时间片的线程只有一个
        System.out.println("叫醒线程叫醒之后休眠开始...");
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    
    public synchronized int get () {
        System.out.println(Thread.currentThread().getName() + " 方法执行了...");
        if(signal != 1) {
            try {
                wait();
                System.out.println("叫醒之后");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(Thread.currentThread().getName() + " 方法执行完毕...");
        return signal;
    }
    
    public static void main(String[] args) {
        
        Demo3 d = new Demo3();
        Target1 t1 = new Target1(d);
        Target2 t2 = new Target2(d);
        
        new Thread(t2).start();
        new Thread(t2).start();
        new Thread(t2).start();
        new Thread(t2).start();
        
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        
        new Thread(t1).start();
        
    }
}