一個線程打印A，一個線程打印B，一個線程打印C，實現(xiàn)循環(huán)打印ABC 10次。主函數(shù)有個小地方不懂！

/*功能：三個線程，一個打印A，一個打印B，一個打印C，主函數(shù)實現(xiàn)循環(huán)打印ABCABCABCABC...  共打印10次ABC*/

public class ThreadABC {
    public static void main(String[] args) {
        Print p = new Print();
        
        /*打印A的進(jìn)程*/
        new Thread(new Runnable() {
            public void run() {
                for(int i = 0;i <10;++i){//我設(shè)置的i打印10次啊
                    p.print_A();
        /*為什么只打印 5 次？？？！?。?/
        /*加上下面這行代碼，就能正常打印10次，why？？？*/
                    //try{Thread.sleep();}catch(Exception e){;}
                }
                
            }
        }).start();
        
        /*啟動打印B的線程*/
        new Thread(new Runnable() {
            public void run() {
                while(true)
                p.print_B();
            }
        }).start();
        
        /*啟動打印C的線程*/
        new Thread(new Runnable() {
            public void run() {
                while(true)
                p.print_C();
            }
        }).start();
    }
}

/**/
class Print {
    /*flag用來同步*/
    private int flag = 1;
    /*打印 A */
    synchronized void print_A() {
        
        if(flag == 1) {
            System.out.print("A");
            flag = 2;
            try {this.notifyAll();}catch(Exception e) {e.printStackTrace();}
        }
        else {
            try {this.wait();}catch(Exception e) {e.printStackTrace();}
        }
    }
    /*打印B*/
    synchronized void print_B() {
        if(flag == 2) {
            System.out.print("B");
            flag = 3;
            try {this.notifyAll();}catch(Exception e) {e.printStackTrace();}
        }
        else {
            try {this.wait();}catch(Exception e) {e.printStackTrace();}
        }
    }
    /*打印C*/
        synchronized void print_C() {
        if(flag == 3) {
            System.out.println("C");
            flag = 1;
            try {this.notifyAll();}catch(Exception e) {e.printStackTrace();}
        }
        else {
            try {this.wait();}catch(Exception e) {e.printStackTrace();}
        }
    }
}