wait() 和 notifyAll（）的一个设计题

Question

Suppose we wish instead to implement a class of blocking counters;
for such counters, an inc() operation should block only if the counter is maxed
out, and proceed only when it is not. Is the approach below a good one? Explain
why or why not.

public class BoundedCounterThreadSafe {
    private int value;
    private int upperBound;
    public synchronized int current(); // Return value
    public synchronized void reset(); // Reset value to 0
    public synchronized boolean isMaxed(); // Return true if value is maxed out
    public synchronized void inc(); // Increment value if < upperBound
}
public class BlockingCounter {
    private BoundedCounterThreadSafe c;
    ....
    public synchronized void inc() throws InterruptedException {
    while (c.isMaxed()) {
        wait();
    }
    c.inc();
    notifyAll();
}
....
}

题目的意思就是这个设计是不是一个好的设计？为什么？谢谢大神回答！

Answer 1

public class BlockingCounter {
private BoundedCounterThreadSafe c;
....
public synchronized void inc() throws InterruptedException {
synchronized(c){//锁定c，保证在Wait前，其它线程都不能修改c
if (c.isMaxed()) {//不用while，while,因为c已经锁定，如果达到max那就直接等待其它线程消费value后唤醒该线程
c.wait();
}
c.inc();
c.notifyAll();//唤醒其它等待消费的线程进行消费
}
}
....
}