java 多线程（生产者消费者）

转 https://www.oschina.net/code/snippet_111708_25438

这个问题挺经典，我这个解法的本质在于将问题抽象为生产者消费者模型，但是是一个特殊的生产者消费者模型，有两点要求：
1、缓冲区大小为1（用一个布尔变量表示就可以了）
2、缓冲区初始为空
再具体点可以将其想象为一个一次只能放一张纸打印的打印机，放纸的线程是A，打印的线程是B。初始状态打印机没有纸。

// 打印机类

public class Printer {

     

    private boolean hasBufferToPrint = false;   // 打印缓冲区是否有内容可以打印

 

    // 打印A：相当于生产者，放一张纸

    public synchronized void printA() {

        while(hasBufferToPrint) {   // 缓冲区还有内容

            try {

                wait();

            } catch (InterruptedException e) {

                e.printStackTrace();

            }

        }

         

        System.out.print("A");

        hasBufferToPrint = true;

         

        notify();   // 唤醒打印B的线程

    }

     

    // 打印B：相当于消费者，消耗缓冲区中的纸，打印纸张

    public synchronized void printB() {

        while (!hasBufferToPrint) {

            try {

                wait();

            } catch (InterruptedException e) {

                e.printStackTrace();

            }

        }

         

        System.out.print("B");

        hasBufferToPrint = false;

         

        notify();   // 唤醒打印A的线程

    }

 

    static class ThreadA extends Thread {

        private Printer printer;

 

        public ThreadA(Printer printer) {

            this.printer = printer;

        }

 

        public void run() {

            for(int i = 0; i < 10; i++) {

                printer.printA();

            }

        }

    }

 

    static class ThreadB extends Thread {

        private Printer printer;

         

        public ThreadB(Printer printer) {

            this.printer = printer;

        }

         

        public void run() {

            for(int i = 0; i < 10; i++) {

                printer.printB();

            }

        }

    }

 

    public static void main(String args[]) {

        Printer printer = new Printer();   // A、B线程共享同一个打印机

        Thread a = new ThreadA(printer);

        Thread b = new ThreadB(printer);

         

        a.start();

        b.start();

    }

}