Condition類的signal則是喚醒被Condition類使用await作用的那個執行緒，它會有針對性的喚醒執行緒，而不是隨機喚醒一個執行緒，以保證執行緒執行的順序：

package com.yzh.job.test;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class Thread3 {
	public static void main(String[] args) {
		final G g = new G();
		Thread t1 = new Thread(){
			@Override
			public void run(){
				String str = "Thread1";
				g.show1(str);
			}
		};
		Thread t2 = new Thread(){
			@Override
			public void run(){
				String str = "Thread2";
				g.show2(str);
			}
		};
		
		Thread t3 = new Thread(){
			@Override
			public void run(){
				String str = "Thread3";
				g.show3(str);
			}
		};
		t1.start();
		t2.start();
		t3.start();
	}
}

class G{
	//注意要寫在方法外面
	Lock lock = new ReentrantLock();
	//有幾個執行緒就定義幾個condition物件
	Condition c1 = lock.newCondition();
	Condition c2 = lock.newCondition();
	Condition c3 = lock.newCondition();
	int i = 3;
	public void show1(String str){
		lock.lock();
		if(i != 3){
			try {
				c3.await();//相當於鎖住當前這一個執行緒，釋放鎖
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		for(int i = 0;i<1;i++){
			System.out.println(str);
		}
		i = 2;
		//喚醒c2那一個作用的執行緒：指定執行緒喚醒
		try {
			c2.signal();
		} catch (Exception e) {
			e.printStackTrace();
		}
		lock.unlock();
	} 
	
	public void show2(String str){
		lock.lock();
		if(i != 2){
			try {
				c2.await();//相當於鎖住當前這一個執行緒，釋放鎖
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		for(int i = 0;i<2;i++){
			System.out.println(str);
		}
		i = 1;
		//喚醒c1那一個作用的執行緒：指定執行緒喚醒
		try {
			c1.signal();
		} catch (Exception e) {
			e.printStackTrace();
		}
		lock.unlock();
	} 
	
	public void show3(String str){
		lock.lock();
		if(i != 1){
			try {
				//釋放當前鎖
				c1.await();//相當於鎖住當前這一個執行緒，釋放鎖
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		for(int i = 0;i<3;i++){
			System.out.println(str);
		}
		i = 3;
		//喚醒c3那一個作用的執行緒：指定執行緒喚醒
		try {
			c3.signal();
		} catch (Exception e) {
			e.printStackTrace();
		}
		lock.unlock();
	} 
}