面试多线程题

多线程打印奇偶数

Sychronized写法

public class PrintOddEven {
    private static int MAX_COUNT = 10;
    private static int num = 1;
    private static Object lock = new Object();

    public static void print(int isOdd) {
        for (int i = 0; i < MAX_COUNT; i++) {
            synchronized (lock) {
                while (num % 2 != isOdd) {
                    try {
                        lock.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }

                System.out.println(Thread.currentThread().getName() + ": " + num);
                num++;
                lock.notify();
            }
        }
    }

    public static void main(String[] args) throws InterruptedException {
        Thread threadA = new Thread(new Runnable() {
            @Override
            public void run() {
                print(0);
            }
        }, "Thread-a");

        Thread threadB = new Thread(new Runnable() {
            @Override
            public void run() {
                print(1);
            }
        }, "Thread-b");

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

        threadA.join();
        threadB.join();
    }
}

ReentrantLock写法

public class PrintOddEvenReentrant {
    private static int MAX_COUNT = 10;
    private static int num = 1;
    private static ReentrantLock lock = new ReentrantLock();
    private static Condition odd = lock.newCondition();
    private static Condition even = lock.newCondition();

    public static void printOdd() {
        for (int i = 0; i < MAX_COUNT; i++) {
            lock.lock();
            try {
                while (num % 2 != 1) {
                    odd.await();
                }
                System.out.println(Thread.currentThread().getName() + ": " + num);
                num++;
                even.signal();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            } finally {
                lock.unlock();
            }
        }
    }

    public static void printEven() {
        for (int i = 0; i < MAX_COUNT; i++) {
            lock.lock();
            try {
                while (num % 2 != 0) {
                    even.await();
                }
                System.out.println(Thread.currentThread().getName() + ": " + num);
                num++;
                odd.signal();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            } finally {
                lock.unlock();
            }
        }
    }

    public static void main(String[] args) throws InterruptedException {
        Thread threadA = new Thread(new Runnable() {
            @Override
            public void run() {
                printOdd();
            }
        }, "Thread-a");

        Thread threadB = new Thread(new Runnable() {
            @Override
            public void run() {
                printEven();
            }
        }, "Thread-b");

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

        threadA.join();
        threadB.join();
    }
}