synchronized

synchronized

synchronized

解决避免临界区的竞态条件的发生，$synchronized$即俗称的对象锁，它采用互斥的方式让同一时刻至多只有一个线程能持有对象锁，其他线程想要再获取这个对象锁时就会阻塞住，这样就能保证拥有锁的线程可以安全的执行临界区的代码。。

代码

@Slf4j(topic = "c.Test11") public class Test11 { static int count = 0; static final Object lock = new Object(); public static void main(String[] args) throws InterruptedException { Thread t1 = new Thread(() -> { for (int i = 0; i < 5000; i ++) { synchronized (lock) { count ++; } } }); Thread t2 = new Thread(() -> { for (int i = 0; i < 5000; i ++) { synchronized (lock) { count --; } } }); t1.start(); t2.start(); t1.join(); t2.join(); log.debug("count的值是 {}", count); } }

做面向对象的改进

@Slf4j(topic = "c.Test11") public class Test11 { public static void main(String[] args) throws InterruptedException { Room r = new Room(); Thread t1 = new Thread(() -> { for (int i = 0; i < 5000; i ++) { r.increase(); } }); Thread t2 = new Thread(() -> { for (int i = 0; i < 5000; i ++) { r.decrease(); } }); t1.start(); t2.start(); t1.join(); t2.join(); log.debug("count的值是 {}", r.getCount()); } } class Room { private int count = 0; public void increase() { synchronized (this) { count ++; } } public void decrease() { synchronized (this) { count --; } } public int getCount() { return count; } }

加在方法上

class Test { public synchronized void test() {} } //等价于 class Test { public void test() { synchronized (this) { } } } class Test { public synchronized static void test() {} } //等价于 class Test { public void test() { synchronized (Test.this) { } } }

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