两个线程交替打印1-100

一、实现方案

• 使用ReentrantLock
• synchronized同步锁

二、ReentrantLock实现

public class Test {
    private static int maxCount = 100;
    private static volatile int num = 1;
    private static Lock lock = new ReentrantLock();
    private static Condition oddCondition = lock.newCondition();
    private static Condition evenCondition = lock.newCondition();

    public static void main(String[] args) {
        Thread oddThread = new Thread(() -> {
            printOdd();
        }, "OddThread");

        Thread evenThread = new Thread(() -> {
            printEven();
        }, "EvenThread");

        oddThread.start();
        evenThread.start();
    }

    private static void printOdd() {
        while (num <= maxCount) {
            try {
                lock.lock();
                if (num % 2 != 0) {
                    System.out.println("printOdd " + num);
                    num++;
                }
                evenCondition.signal();
                oddCondition.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }

    }

    private static void printEven() {
        while (num <= maxCount) {
            try {
                lock.lock();
                if (num % 2 == 0) {
                    System.out.println("printEven " + num);
                    num++;
                }
                oddCondition.signal();
                evenCondition.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    }
}

public class Test {

    public volatile static int count = 1;

    public static void main(String[] args) throws Exception {
        System.out.println("start....");
        ReentrantLock lock = new ReentrantLock();
        Condition condition1 = lock.newCondition();
        Condition condition2 = lock.newCondition();
        Condition condition3 = lock.newCondition();

        new Thread(() -> {
            while (count < 100) {
                try {
                    lock.lock();

                    if (count % 3 == 1) {
                        System.out.println("threadA:" + count);
                        count++;
                        condition2.signal();
                        condition1.await();
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    lock.unlock();
                }
            }

        }, "threadA").start();

        new Thread(() -> {
            while (count < 100) {
                try {
                    lock.lock();

                    if (count % 3 == 2) {
                        System.out.println("threadB:" + count);
                        count++;
                        condition3.signal();
                        condition2.await();
                    }

                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    lock.unlock();
                }
            }

        }, "threadB").start();

        new Thread(() -> {
            while (count < 100) {
                try {
                    lock.lock();

                    if (count % 3 == 0) {
                        System.out.println("threadC:" + count);
                        count++;
                        condition1.signal();
                        condition3.await();
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    lock.unlock();
                }
            }

        }, "threadC").start();
    }
}

三、synchronized同步锁

public class Test {
    private static int maxCount = 100;
    private static int num = 1;
    private static Object lock = new Object();

    public static void main(String[] args) {
        Thread oddThread = new Thread(() -> {
            printOdd();
        }, "OddThread");

        Thread evenThread = new Thread(() -> {
            printEven();
        }, "EvenThread");

        oddThread.start();
        evenThread.start();
    }

    private static void printOdd() {
        while (num <= maxCount) {
            try {
                synchronized (lock) {
                    if (num % 2 != 0) {
                        System.out.println("printOdd " + num);
                        num++;
                        lock.notify();
                        lock.wait();
                    }
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

    }

    private static void printEven() {
        while (num <= maxCount) {
            try {
                synchronized (lock) {
                    if (num % 2 == 0) {
                        System.out.println("printEven " + num);
                        num++;
                        lock.notify();
                        lock.wait();
                    }
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}