Gientxk
Gientxk
2017-11-24 11:13

多线程问题:使用两个线程交替打印A和B,使用最大打印次数控制,详见代码。

  • 多线程

多线程问题:使用两个线程交替打印A和B,使用最大打印次数控制,详见代码。
出现的问题是:当运行线程B中的run()方法时,程序没有先while()判断,而是直接进入了while循环体。

 /**
 * 共享资源:打印机
 * @author Tangxkun
 *
 */
public class Printer {

    //最大打印次数
    private final int MAX_COUNT = 7;
    //false表示该打印机未打印A,true表示该打印机正在打印A
    private boolean printingA = false;
    private int count = 0;

    public synchronized void printA(){
        System.out.print(count++);
        printingA = true;
        System.out.print("A-");
        notifyAll();
    }
    public synchronized void printB(){
        System.out.print(count++);
        printingA = false;
        System.out.print("B-");
        notifyAll();
    }
    public synchronized void aWaiting() throws InterruptedException{
        while(printingA == true){
            wait();
        }
    }
    public synchronized void bWaiting() throws InterruptedException{
        while(printingA == false){
            wait();
        }
    }

    public int getCount() {
        return count;
    }
    public void setCount(int count) {
        this.count = count;
    }
    public int getMAX_COUNT() {
        return MAX_COUNT;
    }
}
 /**
 * 打印A的线程
 * @author Tangxkun
 *
 */
public class PrintA implements Runnable{

    private Printer printer;

    public PrintA(Printer printer) {
        super();
        this.printer = printer;
    }

    @Override
    public void run() {
        while(printer.getCount() < printer.getMAX_COUNT()){

            printer.printA();

            try {
                printer.aWaiting();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }
    }

}
 /**
 * 打印B的线程
 * @author Tangxkun
 *
 */
public class PrintB implements Runnable{

    private Printer printer;

    public PrintB(Printer printer) {
        super();
        this.printer = printer;
    }

    @Override
    public void run() {
        while(printer.getCount() < printer.getMAX_COUNT()){

            try {
                printer.bWaiting();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            printer.printB();

        }
    }

}
 /**
 * 测试代码
 * @author Tangxkun
 *
 */
public class Test {

    public static void main(String[] args) {

        Printer printer = new Printer();
        PrintA printA = new PrintA(printer);
        PrintB printB = new PrintB(printer);

        Thread threadA = new Thread(printA,"A");
        Thread threadB = new Thread(printB, "B");

        threadA.start();
        threadB.start();

    }
}

当设置MAX_COUNT=5时,输出结果为:图片说明

当设置MAX_COUNT=6时,输出结果为:图片说明

当设置MAX_COUNT=7时,输出结果为:图片说明

烧脑了半天还是没有找出端倪,所以来请教一下各位大神!

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