多线程通信 wait和notify

一、概念
  线程是操作系统中独立的个体，这些线程如果不通过特殊的手段进行处理，就无法组成一个完整的整体。因此线程通信就称为组成一个整体的必须条件之一。当线程之间存在通信，那么系统之间的交互就会更加强大。在提高CPU使用率的前提下，会使开发人员对线程任务在开发的过程中进行有效的把控和监督。
   使用wait/notify实现线程之间的通信。这两个方法都是Object的类方法。也就是java的所有对象都提供了这两个方法。
   wait/notify必须配合关键字synchronize使用
   wait方法是释放锁，notify方法是不释放锁
1.异步通信

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;

 
public class ListAdd2 {
	private volatile static List list = new ArrayList();	
	
	public void add(){
		list.add("bjsxt");
	}
	public int size(){
		return list.size();
	}
	
	public static void main(String[] args) {
		
		final ListAdd2 list2 = new ListAdd2();
		final Object lock = new Object();
		Thread t1 = new Thread(new Runnable() {
			@Override
			public void run() {
				try {
					synchronized (lock) {
						System.out.println("t1启动..");
						for(int i = 0; i <10; i++){
							list2.add();
							System.out.println("当前线程：" + Thread.currentThread().getName() + "添加了一个元素..");
							Thread.sleep(500);
							if(list2.size() == 5){
								System.out.println("已经发出通知..");
								lock.notify();
							}
						}						
					}
				} catch (InterruptedException e) {
					e.printStackTrace();
				}

			}
		}, "t1");
		
		Thread t2 = new Thread(new Runnable() {
			@Override
			public void run() {
				synchronized (lock) {
					System.out.println("t2启动..");
					if(list2.size() != 5){
						try {
							lock.wait();
						} catch (InterruptedException e) {
							e.printStackTrace();
						}
					}
					System.out.println("当前线程：" + Thread.currentThread().getName() + "收到通知线程停止..");
					throw new RuntimeException();
				}
			}
		}, "t2");	
		t2.start(); // 注意此处，t2线程先启动
		t1.start();
		
	}
	
}

2.实时通信

public class ListAdd3 {
    private volatile static List list = new ArrayList();

    final static CountDownLatch countDownLatch = new CountDownLatch(1);  // 数字表示发起几次通知，线程才会被唤醒，如果为2，则需要写两次通知，如代码中注释

    public void add(){
        list.add("bjsxt");
    }
    public int size(){
        return list.size();
    }

    public static void main(String[] args) {

        final ListAdd3 list2 = new ListAdd3();
        final Object lock = new Object();
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                  //  synchronized (lock) {
                        System.out.println("t1启动..");
                        for(int i = 0; i <10; i++){
                            list2.add();
                            System.out.println("当前线程：" + Thread.currentThread().getName() + "添加了一个元素..");
                            Thread.sleep(500);
                            if(list2.size() == 5){
                                System.out.println("已经发出通知..");
                                countDownLatch.countDown();
                                //countDownLatch.countDown(); // 如果括号中数字为2，则这里写几次
                               // lock.notify();
                            }
                        }
                   // }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

            }
        }, "t1");

        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                //synchronized (lock) {
                    System.out.println("t2启动..");
                    if(list2.size() != 5){
                        try {
                            //lock.wait();
                            countDownLatch.await();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                    System.out.println("当前线程：" + Thread.currentThread().getName() + "收到通知线程停止..");
                    throw new RuntimeException();
                }
           // }
        }, "t2");
        t2.start();
        t1.start();

    }

}

import java.util.ArrayList;
import java.util.List;

public class ListAdd1 {

	private volatile static List list = new ArrayList();	
	
	public void add(){
		list.add("bjsxt");
	}
	public int size(){
		return list.size();
	}
	
	public static void main(String[] args) {
		
		final ListAdd1 list1 = new ListAdd1();
		
		Thread t1 = new Thread(new Runnable() {
			@Override
			public void run() {
				try {
					for(int i = 0; i <10; i++){
						list1.add();
						System.out.println("当前线程：" + Thread.currentThread().getName() + "添加了一个元素..");
						Thread.sleep(500);
					}	
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		}, "t1");
		
		Thread t2 = new Thread(new Runnable() {
			@Override
			public void run() {
				while(true){
					if(list1.size() == 5){
						System.out.println("当前线程收到通知：" + Thread.currentThread().getName() + " list size = 5 线程停止..");
						throw new RuntimeException();
					}
				}
			}
		}, "t2");		
		
		t1.start();
		t2.start();
	}
	
	
}