面试题：启动3个线程打印递增的数字.........

浅浅的花香味﹌ 2024-04-17 16:41 37阅读 0赞

附加题---需要使用synchronized和lock两种方式来完成  
1：启动3个线程打印递增的数字, 线程1先打印1,2,3,4,5, 然后是线程2打印6,7,8,9,10, 然后是线程3打印11,12,13,14,15. 接着再由线程1打印16,17,18,19,20....以此类推, 直到打印到75. 程序的输出结果应该为:

线程1: 1  
线程1: 2  
线程1: 3  
线程1: 4  
线程1: 5

线程2: 6  
线程2: 7  
线程2: 8  
线程2: 9  
线程2: 10  
...  
线程3: 71  
线程3: 72  
线程3: 73  
线程3: 74  
线程3: 75

解题思路：先定义一个int数，默认为1，表示从1开始，接着定义一个标识，来控制锁对象 ，利用分离的思想创建三个方法。

synchronized方式

public class PrintNum {
    	public int num=1;//从1开始打印
    	public int isPrint=1;//标识，1,2,3中标识分别代表三种状态
    	//synchronized方式
    	//方法一   标识1
    	public synchronized void fun1() {
    		while (isPrint!=1) {
    			try {
    				wait();
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    		}
    		
    		printXunHuan();
    		
    		isPrint=2;
    		notifyAll();
    	}
    	
    	//方法二   标识2
    	public synchronized void fun2() {
    		while (isPrint!=2) {
    			try {
    				wait();
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    		}
    		
    		printXunHuan();
    		
    		isPrint=3;
    		notifyAll();
    	}
    	
    	//方法三 标识3
    	public synchronized void fun3() {
    		while (isPrint!=3) {
    			try {
    				wait();
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    		}
    		printXunHuan();
    		isPrint=1;
    		notifyAll();
    	}
    	public void printXunHuan() {
    		for (int i = 0; i < 5; i++) {
    			System.out.println(Thread.currentThread().getName()+":"+num++);
    
    			try {
    				Thread.sleep(500);
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    		}
    	}
    	
    	
    }

import com.qf.bean.PrintNum;
    
    public class PrintNumTest {
    	
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
    		PrintNum printNum=new PrintNum();
    		//线程1
    		new Thread(new Runnable() {
    			
    			@Override
    			public void run() {
    				// TODO Auto-generated method stub
    				while (printNum.num<=65) {
    					printNum.fun1();
    				}
    			}
    		}, "线程1").start();
    		
    		//线程2
    		new Thread(new Runnable() {
    			
    			@Override
    			public void run() {
    				// TODO Auto-generated method stub
    				while (printNum.num<=70) {
    					printNum.fun2();
    				}
    			}
    		}, "线程2").start();
    		
    		//线程3
    		new Thread(new Runnable() {
    			
    			@Override
    			public void run() {
    				// TODO Auto-generated method stub
    				while (printNum.num<=75) {
    					printNum.fun3();
    				}
    			}
    		}, "线程3").start();
    	}
    
    }

lock方式

import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    public class PrintNumLock {
    	private int num=1;//从1开始
    	private int isPrint=1;//标识  1,2,3
    	public int getNum() {
    		return num;
    	}
    	public void setNum(int num) {
    		this.num = num;
    	}
    	public PrintNumLock() {
    		super();
    	}
    	
    	final Lock lock=new ReentrantLock();
    	final Condition oneCondition=lock.newCondition();
    	final Condition twoCondition=lock.newCondition();
    	final Condition threeCondition=lock.newCondition();
    	
    	//锁1
    	public void funOne() {
    		lock.lock();
    		try {
    			while (isPrint!=1) {
    				try {
    					oneCondition.await();
    				} catch (InterruptedException e) {
    					// TODO Auto-generated catch block
    					e.printStackTrace();
    				}
    			}
    			
    			printXunHuan();
    			
    			isPrint=2;//切换标识2  唤醒锁2
    			twoCondition.signal();
    			
    		} finally {
    			// TODO: handle finally clause
    			lock.unlock();
    		}
    	}
    	
    	//锁2
    	public void funTwo() {
    		lock.lock();
    		try {
    			while (isPrint!=2) {
    				try {
    					twoCondition.await();
    				} catch (InterruptedException e) {
    					// TODO Auto-generated catch block
    					e.printStackTrace();
    				}
    			}
    			
    			printXunHuan();
    			
    			isPrint=3;//切换标识3  唤醒锁3
    			threeCondition.signal();
    			
    		} finally {
    			// TODO: handle finally clause
    			lock.unlock();
    		}
    	}
    	
    	//锁3
    	public void funThree() {
    		lock.lock();
    		try {
    			while (isPrint!=3) {
    				try {
    					threeCondition.await();
    				} catch (InterruptedException e) {
    					// TODO Auto-generated catch block
    					e.printStackTrace();
    				}
    			}
    
    			printXunHuan();
    			
    			isPrint=1;//切换为标识1  唤醒锁1
    			oneCondition.signal();
    		} finally {
    			// TODO: handle finally clause
    			lock.unlock();
    		}
    	}
    	//控制循环5次
    	public void printXunHuan() {
    		for (int i = 0; i < 5; i++) {
    			System.out.println(Thread.currentThread().getName()+":"+num++);
    
    			try {
    				Thread.sleep(500);
    			} catch (InterruptedException e) {
    				// TODO Auto-generated catch block
    				e.printStackTrace();
    			}
    		}
    	}
    }

import com.qf.bean.PrintNumLock;
    
    public class PrintNumLockTest {
    	
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
    		PrintNumLock printnum=new PrintNumLock();
    		new Thread(new Runnable() {
    			
    			@Override
    			public void run() {
    				// TODO Auto-generated method stub
    				while (printnum.getNum()<=65) {
    					printnum.funOne();
    				}
    			}
    		}, "线程1").start();
    		
    		new Thread(new Runnable() {
    			
    			@Override
    			public void run() {
    				// TODO Auto-generated method stub
    				while (printnum.getNum()<=70) {
    					printnum.funTwo();
    				}
    			}
    		}, "线程2").start();
    		
    		new Thread(new Runnable() {
    			
    			@Override
    			public void run() {
    				// TODO Auto-generated method stub
    				while (printnum.getNum()<=75) {
    					printnum.funThree();
    				}
    			}
    		}, "线程3").start();
    		
    	}
    
    }

本题还有简单的解法 ，就是把三个方法合并为一个进行控制。大家有兴趣可以试试。。。。。