public class MyObject {

  synchronized public void methodA() {
    //do something....
  }

  synchronized public void methodB() {
    //do some other thing
  }
}

public class ThreadA extends Thread {

  private MyObject object;
//省略构造方法
  @Override
  public void run() {
    super.run();
    object.methodA();
  }
}

public class ThreadB extends Thread {

  private MyObject object;
//省略构造方法
  @Override
  public void run() {
    super.run();
    object.methodB();
  }
}

public class Run {
  public static void main(String[] args) {
    MyObject object = new MyObject();

    //线程A与线程B 持有的是同一个对象:object
    ThreadA a = new ThreadA(object);
    ThreadB b = new ThreadB(object);
    a.start();
    b.start();
  }
}

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

public class MyList {

  private List<String> list = new ArrayList<String>();
  public void add() {
    list.add("elements");
  }
  public int size() {
    return list.size();
  }
}

import mylist.MyList;

public class ThreadA extends Thread {

  private MyList list;

  public ThreadA(MyList list) {
    super();
    this.list = list;
  }

  @Override
  public void run() {
    try {
      for (int i = 0; i < 10; i++) {
        list.add();
        System.out.println("添加了" + (i + 1) + "个元素");
        Thread.sleep(1000);
      }
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
}

import mylist.MyList;

public class ThreadB extends Thread {

  private MyList list;

  public ThreadB(MyList list) {
    super();
    this.list = list;
  }

  @Override
  public void run() {
    try {
      while (true) {
        if (list.size() == 5) {
          System.out.println("==5, 线程b准备退出了");
          throw new InterruptedException();
        }
      }
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
}

import mylist.MyList;
import extthread.ThreadA;
import extthread.ThreadB;

public class Test {

  public static void main(String[] args) {
    MyList service = new MyList();

    ThreadA a = new ThreadA(service);
    a.setName("A");
    a.start();

    ThreadB b = new ThreadB(service);
    b.setName("B");
    b.start();
  }
}

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

public class MyList {

  private static List<String> list = new ArrayList<String>();

  public static void add() {
    list.add("anyString");
  }

  public static int size() {
    return list.size();
  }
}


public class ThreadA extends Thread {

  private Object lock;

  public ThreadA(Object lock) {
    super();
    this.lock = lock;
  }

  @Override
  public void run() {
    try {
      synchronized (lock) {
        if (MyList.size() != 5) {
          System.out.println("wait begin "
              + System.currentTimeMillis());
          lock.wait();
          System.out.println("wait end "
              + System.currentTimeMillis());
        }
      }
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
}


public class ThreadB extends Thread {
  private Object lock;

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

  @Override
  public void run() {
    try {
      synchronized (lock) {
        for (int i = 0; i < 10; i++) {
          MyList.add();
          if (MyList.size() == 5) {
            lock.notify();
            System.out.println("已经发出了通知");
          }
          System.out.println("添加了" + (i + 1) + "个元素!");
          Thread.sleep(1000);
        }
      }
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
}

public class Run {

  public static void main(String[] args) {

    try {
      Object lock = new Object();

      ThreadA a = new ThreadA(lock);
      a.start();

      Thread.sleep(50);

      ThreadB b = new ThreadB(lock);
      b.start();
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
}