三种写法

public class Thread5 {
    private static int num = 0;
    private static int MAX_NUM = 20;
    private static Object lock = new Object();

    public static void subNum() {
        synchronized (lock) {
            while (num == 0) {
                try {
                    lock.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            num--;
            try {
                Thread.sleep(0);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            lock.notifyAll();
            System.out.println(Thread.currentThread().getName() + ",当前num: " + num + ",消费: " + 1);
        }
    }

    public static void addNum() {
        synchronized (lock) {
            while (num == MAX_NUM) {
                try {
                    lock.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            num++;
            try {
                Thread.sleep(0);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            lock.notifyAll();
            System.out.println(Thread.currentThread().getName() + ",当前num: " + num + ",生产: " + 1);
        }
    }

    public static void main(String[] args) {
        for (int i = 0; i < 10; i++) {
            Thread thread = new Thread(new Runnable() {
                @Override
                public void run() {
                    subNum();
                }
            });
            thread.setName("消费者" + i);
            thread.start();
        }
        for (int j = 0; j < 10; j++) {
            Thread t = new Thread(new Runnable() {
                @Override
                public void run() {
                    addNum();
                }
            });
            t.setName("生产者" + j);
            t.start();
        }
    }
}

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class Thread6 {
    private static int num = 0;
    private static int MAX_NUM = 20;
    private static Lock lock = new ReentrantLock();
    private static Condition full = lock.newCondition();
    private static Condition empty = lock.newCondition();

    public static void subNum() {
        lock.lock();
        while (num == 0) {
            try {
                empty.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        num--;
        try {
            Thread.sleep(0);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        full.signalAll();
        System.out.println(Thread.currentThread().getName() + ",当前num: " + num + ",消费: " + 1);
        lock.unlock();
    }

    public static void addNum() {
        lock.lock();
        while (num == MAX_NUM) {
            try {
                full.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        num++;
        try {
            Thread.sleep(0);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        empty.signalAll();
        System.out.println(Thread.currentThread().getName() + ",当前num: " + num + ",生产: " + 1);
        lock.unlock();
    }

    public static void main(String[] args) {
        for (int i = 0; i < 10; i++) {
            Thread thread = new Thread(new Runnable() {
                @Override
                public void run() {
                    subNum();
                }
            });
            thread.setName("消费者" + i);
            thread.start();
        }
        for (int j = 0; j < 10; j++) {
            Thread t = new Thread(new Runnable() {
                @Override
                public void run() {
                    addNum();
                }
            });
            t.setName("生产者" + j);
            t.start();
        }
    }
}

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;

public class Thread7 {
    private static int MAX_NUM = 2;
    private static BlockingQueue<String> queue = new ArrayBlockingQueue<String>(MAX_NUM);

    public static void subNum() {
        try {
            String item = queue.take();
            System.out.println(Thread.currentThread().getName() + ",当前num: " + queue.size() + ",消费: " + 1);

        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void addNum() {
        try {
            queue.put("1");
            System.out.println(Thread.currentThread().getName() + ",当前num: " + queue.size() + ",生产: " + 1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        for (int i = 0; i < 10; i++) {
            Thread thread = new Thread(new Runnable() {
                @Override
                public void run() {
                    subNum();
                }
            });
            thread.setName("消费者" + i);
            thread.start();
        }
        for (int j = 0; j < 10; j++) {
            Thread t = new Thread(new Runnable() {
                @Override
                public void run() {
                    addNum();
                }
            });
            t.setName("生产者" + j);
            t.start();
        }
    }
}