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一、内置锁

• 同步：synchronized
• 协作：Object # wait/notify/notifyAll

public class PrintNumber {    /**     * 打印锁，同一时刻仅有一个任务可以持有此锁     */    private static Object lock = new Object();    /**     * 计数器     */    private static int counter = 1;    /**     * 计数器最大值     */    private static final int MAX_COUNTER = 100;    public static void main(String args[]) {        // 奇数打印线程        Thread oddThread = new Thread() {            @Override            public void run() {                // 请求打印锁                synchronized (lock) {                    while (counter <= MAX_COUNTER) {                        // counter为奇数，打印counter并唤醒偶数打印线程                        if (counter % 2 != 0) {                            System.out.println("Thread1 : " + counter);                            counter = counter + 1;                            lock.notifyAll();                        }                        // counter为偶数，挂起并等待偶数打印线程唤醒                        else {                            try {                                lock.wait();                            } catch (Exception e) {                                e.printStackTrace();                            }                        }                    }                }            }        };        // 偶数打印线程        Thread evenThread = new Thread() {            @Override            public void run() {                // 请求打印锁                synchronized (lock) {                    while (counter <= MAX_COUNTER) {                        // counter为偶数，打印counter并唤醒奇数打印线程                        if (counter % 2 == 0) {                            System.out.println("Thread2 : " + counter);                            counter = counter + 1;                            lock.notifyAll();                        }                        // counter为奇数，挂起并等待奇数打印线程唤醒                        else {                            try {                                lock.wait();                            } catch (Exception e) {                                e.printStackTrace();                            }                        }                    }                }            }        };        oddThread.start();        evenThread.start();    }}

二、显式锁

• 同步：lock/unlock
• 协作：Condition # await/signal/signalAll

public class PrintNumber {    /**     * 打印锁，同一时刻仅有一个任务可以持有此锁     */    private static Lock lock = new ReentrantLock();    private static Condition oddCondition = lock.newCondition();    private static Condition evenCondition = lock.newCondition();    /**     * 计数器     */    private static int counter = 1;    /**     * 计数器最大值     */    private static final int MAX_COUNTER = 100;    public static void main(String args[]) {        // 奇数打印线程        Thread oddThread = new Thread() {            @Override            public void run() {                try {                    // 请求打印锁                    lock.lock();                    while (counter <= MAX_COUNTER) {                        // counter为奇数，打印counter并唤醒偶数打印线程                        if (counter % 2 != 0) {                            System.out.println("Thread1 : " + counter);                            counter = counter + 1;                            evenCondition.signalAll();                        }                        // counter为偶数，挂起并等待偶数打印线程唤醒                        else {                            try {                                oddCondition.await();                            } catch (Exception e) {                                e.printStackTrace();                            }                        }                    }                } finally {                    // 释放打印锁                    lock.unlock();                }            }        };        // 偶数打印线程        Thread evenThread = new Thread() {            @Override            public void run() {                try {                    // 请求打印锁                    lock.lock();                    while (counter <= MAX_COUNTER) {                        // counter为偶数，打印counter并唤醒奇数打印线程                        if (counter % 2 == 0) {                            System.out.println("Thread2 : " + counter);                            counter = counter + 1;                            oddCondition.signalAll();                        }                        // counter为奇数，挂起并等待奇数打印线程唤醒                        else {                            try {                                evenCondition.await();                            } catch (Exception e) {                                e.printStackTrace();                            }                        }                    }                } finally {                    // 释放打印锁                    lock.unlock();                }            }        };        oddThread.start();        evenThread.start();    }}

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