Java synchronized关键字

对象锁

• 同步代码块_对象锁（thread.join可表示为当前线程执行完毕后在进行下一个线程执行）

  • public class SynchronizedObjBlock implements Runnable {
        Object object = new Object();
        Object object2 = new Object();
    
        @Override
        public void run() {
            synchronized (object){
                System.out.println(Thread.currentThread().getName() + "占用🔒OBJ");
                try {
                    Thread.sleep(3000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName()+"釋放🔒OBJ");
            }
            synchronized (object2){
                System.out.println(Thread.currentThread().getName() + "占用🔒OBJ2");
                try {
                    Thread.sleep(3000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName()+"釋放🔒OBJ2");
            }
        }
    
        static SynchronizedObjBlock synchronizedObjBlock = new SynchronizedObjBlock();
        public static void main(String[] args) {
            Thread t1 = new Thread(synchronizedObjBlock);
            Thread t2 = new Thread(synchronizedObjBlock);
            t1.start();
            t2.start();
            while (t1.isAlive() || t2.isAlive()) {
            }
            System.out.println("finish");
        }
    }
    

• 方法锁形式：用以修饰普通方法，锁对象默认为this

  • public class SynchronizedMethodBlock implements Runnable {
        Object object = new Object();
        Object object2 = new Object();
    
        public  synchronized void method() throws InterruptedException {
            System.out.println(Thread.currentThread().getName()+"正在执行");
            Thread.sleep(3000);
            System.out.println(Thread.currentThread().getName()+"结束执行");
        }
        @Override
        public void run() {
            try {
                method();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    
        static SynchronizedMethodBlock synchronizedObjBlock = new SynchronizedMethodBlock();
        public static void main(String[] args) {
            Thread t1 = new Thread(synchronizedObjBlock);
            Thread t2 = new Thread(synchronizedObjBlock);
            t1.start();
            t2.start();
            while (t1.isAlive() || t2.isAlive()) {
            }
            System.out.println("finish");
        }
    }
    
    

类锁

• 对static方法：

  • public class SynchronizedStaticMethodBlock implements Runnable {
        Object object = new Object();
        Object object2 = new Object();
    
        public static synchronized void method() throws InterruptedException {
            System.out.println(Thread.currentThread().getName()+"正在执行");
            Thread.sleep(3000);
            System.out.println(Thread.currentThread().getName()+"结束执行");
        }
        @Override
        public void run() {
            try {
                method();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    
        static SynchronizedStaticMethodBlock synchronizedObjBlock = new SynchronizedStaticMethodBlock();
        static SynchronizedStaticMethodBlock synchronizedObjBlock2 = new SynchronizedStaticMethodBlock();
        public static void main(String[] args) {
            Thread t1 = new Thread(synchronizedObjBlock);
            Thread t2 = new Thread(synchronizedObjBlock2);
            t1.start();
            t2.start();
            while (t1.isAlive() || t2.isAlive()) {
            }
            System.out.println("finish");
        }
    }
    

• synchronized（*.clasa）代码块

  • public class SynchronizedClassBlock implements Runnable {
        Object object = new Object();
        Object object2 = new Object();
    
        public void method() throws InterruptedException {
            synchronized (SynchronizedClassBlock.class) { //点
                System.out.println(Thread.currentThread().getName()+"正在执行");
                Thread.sleep(3000);
                System.out.println(Thread.currentThread().getName()+"结束执行");
            }
        }
        @Override
        public void run() {
            try {
                method();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    
        static SynchronizedClassBlock synchronizedObjBlock = new SynchronizedClassBlock();
        static SynchronizedClassBlock synchronizedObjBlock2 = new SynchronizedClassBlock();
        public static void main(String[] args) {
            Thread t1 = new Thread(synchronizedObjBlock);
            Thread t2 = new Thread(synchronizedObjBlock2);
            t1.start();
            t2.start();
            while (t1.isAlive() || t2.isAlive()) {
            }
            System.out.println("finish");
        }
    }