Javaの虚偽の目覚めとどのように虚偽の目覚めを避けるのか.『マルチスレッド学習の14』

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package duoxiancheng.bao;

/*
 *        ：
 *  wait      while    。
 */
public class LockTest {
    public static void main(String[] args) {
        Clerk clerk = new Clerk();
        Producter producter = new Producter(clerk);
        Customer customer = new Customer(clerk);

        new Thread(producter,"   A").start();
        new Thread(customer,"   A").start();
        new Thread(producter,"   B").start();
        new Thread(customer,"   B").start();
    }
}

//    
class Clerk {
    private int product = 0;

    //   
    public synchronized void add() {
        //     
        while (product >=1) {
            System.out.println(Thread.currentThread().getName() + ": " + "  ！");
            try {
                this.wait();
            } catch (InterruptedException e) {
            }
        }
        ++product;
        //     while      ，      
        System.out.println(Thread.currentThread().getName() + ": " +"....................    ，  "+product);
        this.notifyAll();
    }

    //   
    public synchronized void sale() {
        while (product <=0) {
            System.out.println(Thread.currentThread().getName() + ": " + "     ");
            try {
                this.wait();
            } catch (InterruptedException e) {
            }
        }
        --product;
        System.out.println(Thread.currentThread().getName() + ":     ，   " + product);
        this.notifyAll();
    }
}

//    
class Producter implements Runnable {
    private Clerk clerk;

    public Producter(Clerk clerk) {
        this.clerk = clerk;
    }

    //   
    @Override
    public void run() {
        for(int i = 0; i < 20; ++i) {
            try {
                Thread.sleep(200);
            } catch (InterruptedException e) {
            }
            clerk.add();
        }
    }
}

//    
class Customer implements Runnable {
    private Clerk clerk;
    public Customer(Clerk clerk) {
        this.clerk = clerk;
    }

    //   
    @Override
    public void run() {
        for(int i = 0; i < 20; ++i) {
            clerk.sale();
        }
    }
}

   while (product >=1) {}
     if (product >=1) {}
        

  if      ，          if（）   
 while  ，            while（）