一道很經典的線程筆試題-子線程打印30次，主線程打印20次，如此一輪，循環50輪。

一道很經典的線程筆試題-子線程打印30次，主線程打印20次，如此一輪，循環50輪。

第一種方法

public class Test{

    private boolean isSub = true;
    public synchronized void sub(int i){
        while(!isSub){
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

        
        for(int j=1;j<=30;j++){
            System.out.println("--------------------子線程執行第"+i+"輪，第"+j+"次。");
        }
        
        isSub = false;
        this.notify();
        
    }
    
    public synchronized void master(int i){
        while(isSub){
            try {
                this.wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        
        
        for(int j=1;j<=20;j++){
            System.out.println("主線程執行第"+i+"輪，第"+j+"次。");
        }
        
        isSub = true;
        this.notify();
        
    }
    
    public static void main(String[] args) {
        Test t = new Test();
        new Thread(new Runnable() {
            @Override
            public void run() {
                // TODO Auto-generated method stub
                for(int i=1;i<=50;i++){
                    t.sub(i);
                }
            }
        }).start();
        
        for(int i=1;i<=50;i++){
            t.master(i);
        }
    }
    
}

第二種方法

public class ThreadTest {  
    private static Object object = new Object();  
    public static void main(String[] args) throws InterruptedException {  
        // TODO Auto-generated method stub  
        new Thread(new Runnable() {  
              
            public void run() {  
                // TODO Auto-generated method stub  
                for (int i = 1; i <= 50; i++) {  
                    synchronized (object) {  
                        for (int j = 1; j <= 30; j++) {  
                            System.out.println("--------------------子線程執行第"+i+"輪，第"+j+"次。");  
                        }   
                        object.notify();  
                        try {  
                            object.wait();  
                        } catch (InterruptedException e) {  
                            // TODO Auto-generated catch block  
                            e.printStackTrace();  
                        }                         
                    }  
                }  
            }  
        }).start();  
  
        for(int i = 1; i <= 50; i++){  
            synchronized (object) {  
                object.wait();  
                for (int j = 1; j <= 20; j++) {  
                    System.out.println("主線程執行第"+i+"輪，第"+j+"次。"); 
                }              
                object.notify();                  
            }  
        }  
    }
}