問題：線上程中我們會遇見兩個執行緒之間的通訊，一個執行緒處於等待狀態，另一個執行緒通知才會繼續往下執行。

方法：1、利用object 的wait 和notify 屬性 2、加上鎖synchronized。

package com.thread;


public class ThreadA extends Thread {
Object lock = new Object();


@Override
public void run() {
try {
synchronized (lock) {
ThreadB t = new ThreadB(lock);
t.start();
System.out.println("主執行緒等待");
lock.wait();
System.out.println("我已經睡醒啦，可以繼續工作了");
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}


public static void main(String[] args) {
ThreadA t = new ThreadA();
t.start();
}
}package com.thread;


public class ThreadA extends Thread {
Object lock = new Object();


@Override
public void run() {
try {
synchronized (lock) {
ThreadB t = new ThreadB(lock);
t.start();
System.out.println("主執行緒等待");
lock.wait();
System.out.println("我已經睡醒啦，可以繼續工作了");
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}


public static void main(String[] args) {
ThreadA t = new ThreadA();
t.start();
}
}

package com.thread;


public class ThreadB extends Thread {
Object lock;


public ThreadB(Object lock) {
this.lock = lock;
}


@Override
public void run() {
try {
synchronized (lock) {
System.out.println("執行子執行緒方法");
lock.notify();
Thread.sleep(5000);
System.out.println("我已經喊醒主執行緒，我可以結束了");
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}