转自：http://blog.csdn.net/difffate/article/details/63684290

方法一：通过共享对象锁加上可见变量来实现。

    public class MyService {  
      
        private volatile int orderNum = 1;  
      
        public synchronized void methodA() {  
            try {  
                while (orderNum != 1) {  
                    wait();  
                }  
                for (int i = 0; i < 2; i++) {  
                    System.out.println("AAAAA");  
                }  
                orderNum = 2;  
                notifyAll();  
            } catch (InterruptedException e) {  
                e.printStackTrace();  
            }  
        }  
      
        public synchronized void methodB() {  
            try {  
                while (orderNum != 2) {  
                    wait();  
                }  
                for (int i = 0; i < 2; i++) {  
                    System.out.println("BBBBB");  
                }  
                orderNum = 3;  
                notifyAll();  
            } catch (InterruptedException e) {  
                e.printStackTrace();  
            }  
        }  
      
        public synchronized void methodC() {  
            try {  
                while (orderNum != 3) {  
                    wait();  
                }  
                for (int i = 0; i < 2; i++) {  
                    System.out.println("CCCCC");  
                }  
                orderNum = 1;  
                notifyAll();  
            } catch (InterruptedException e) {  
                e.printStackTrace();  
            }  
        }  
    }  

import service.MyService;  
public class ThreadAA extends Thread {  
  
    private MyService dbtools;  
  
    public ThreadAA(MyService dbtools) {  
        super();  
        this.dbtools = dbtools;  
    }  
  
    @Override  
    public void run() {  
        dbtools.methodA();  
    }  
  
}  

import service.MyService;  
public class ThreadBB extends Thread {  
  
    private MyService dbtools;  
  
    public ThreadBB(MyService dbtools) {  
        super();  
        this.dbtools = dbtools;  
    }  
  
    @Override  
    public void run() {  
        dbtools.methodB();  
    }  
  
}  

import service.MyService;  
public class ThreadCC extends Thread {  
  
    private MyService dbtools;  
  
    public ThreadCC(MyService dbtools) {  
        this.dbtools = dbtools;  
    }  
  
    @Override  
    public void run() {  
        dbtools.methodC();  
    }  
  
}  

import extthread.ThreadCC;  
import service.MyService;  
import extthread.ThreadAA;  
import extthread.ThreadBB;  
  
public class Run {  
  
    public static void main(String[] args) {  
        MyService myService = new MyService();  
        for (int i = 0; i < 2; i++) {  
            ThreadBB output = new ThreadBB(myService);  
            output.start();  
            ThreadAA input = new ThreadAA(myService);  
            input.start();  
            ThreadCC threadCC = new ThreadCC(myService);  
            threadCC.start();  
        }  
    }  
  
}  

可以看到线程的启动按顺序执行了。共享对象锁，可以保证每个方法只能同时有一个线程进入，配合wait和notifyall方法，可以启动或者唤醒线程。

方法二：通过主线程Join()

class T11 extends Thread {  
    public void run() {  
        System.out.println("in T1");  
    }  
}  
  
class T22 extends Thread {  
    public void run() {  
        System.out.println("in T2");  
    }  
}  
  
class T33 extends Thread {  
    public void run() {  
        System.out.println("in T3");  
    }  
}  
  
public class Test2 {  
    public static void main(String[] args) throws InterruptedException {  
        T11 t1 = new T11();  
        T22 t2 = new T22();  
        T33 t3 = new T33();  
        t1.start();  
        t1.join();  
        t2.start();  
        t2.join();  
        t3.start();  
    }  
}  

方法三：通过线程执行时Join()

class T1 extends Thread {  
    public void run(){  
        Random random = new Random();  
        try {  
            Thread.sleep(random.nextInt(1000));  
        } catch (InterruptedException e) {  
            e.printStackTrace();  
        }  
        System.out.println("in T1");  
    }  
}  
  
class T2 extends Thread{  
    private Thread thread;  
    public T2(Thread thread) {  
        this.thread = thread;  
    }  
  
    public void run(){  
        try {  
            thread.join();  
        } catch (InterruptedException e) {  
            e.printStackTrace();  
        }  
        System.out.println("in T2");  
    }  
}  
  
class T3 extends Thread{  
    private Thread thread;  
    public T3(Thread thread) {  
        this.thread = thread;  
    }  
  
    public void run(){  
        try {  
            thread.join();  
        } catch (InterruptedException e) {  
            e.printStackTrace();  
        }  
        System.out.println("in T3");  
    }  
}  
  
public class Test {  
    public static void main(String[] args) throws InterruptedException {  
        T1 t1 = new T1();  
        T2 t2 = new T2(t1);  
        T3 t3 = new T3(t2);  
        t2.start();  
        t1.start();  
        t3.start();  
    }  
}