一道经典的Java多线程编程题

清疚 2022-06-04 03:10 124阅读 0赞

问题描述  
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

解法一：

class PrintRunnable implements Runnable \{

private static volatile int printNum = 0;
    private int threadId;
    private Object o;
    public PrintRunnable(int threadId,Object o){
        this.threadId = threadId;
        this.o=o;
    }
    @Override
    public void run() {
        while(printNum < 75){
            synchronized (o){
                if (printNum/5%3 + 1 == threadId){
                //该判断确保对应线程输出
                    for (int i = 0; i <5; i++) {
                        System.out.println("线程"+threadId+":"+(++printNum));
                    }
                    o.notifyAll();
                }else {
                    try {
                        o.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
    
            }
        }
    }

\}  
public class Main \{  
public static void main(String\[\] args) throws InterruptedException \{  
Object o = new Object();  
new Thread(new PrintRunnable(1,o)).start();  
new Thread(new PrintRunnable(2,o)).start();  
new Thread(new PrintRunnable(3,o)).start();  
\}  
\}  
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
21  
22  
23  
24  
25  
26  
27  
28  
29  
30  
31  
32  
33  
34  
35  
36  
37  
38  
39  
解法二：

public class Print123456 implements Runnable\{  
private String name;  
private Object prev;  
private Object self;  
private int count;  
public Print123456(String name,Object prev,Object self,int count)\{  
this.name=name;  
this.prev=prev;  
this.self=self;  
this.count=count;  
\}  
@Override  
public void run() \{  
while(count<=75)\{  
synchronized (prev)\{  
synchronized (self)\{  
for (int i=0;i<5;i++)\{  
count=count+1;  
if(count>75)break;  
System.out.println(name+”: “+count);

}
                    count=count+10;
                    //System.out.println("释放自身锁，并唤醒在等待该锁的线程");
                    self.notify();//释放自身锁，并唤醒在等待该锁的线程
    
                }
                //System.out.println("释放自身锁成功");
                try {
                    //System.out.println("等待前一个锁");
                    prev.wait();//等待前一个锁
    
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            //System.out.println("两个锁全部释放，重新进入新的循环，但是由于有prev.wait()所以该线程等待获取prev的锁");
        }
    }

\}  
public class Main \{  
public static void main(String\[\] args) throws InterruptedException \{  
Object a=new Object();  
Object b=new Object();  
Object c=new Object();  
Print123456 A=new Print123456(“线程1”,c,a,0);  
Print123456 B=new Print123456(“线程2”,a,b,5);  
Print123456 C=new Print123456(“线程3”,b,c,10);  
new Thread(A).start();  
Thread.sleep(100);  
new Thread(B).start();  
Thread.sleep(100);  
new Thread(C).start();  
Thread.sleep(100);  
\}  
\}