java基础---->多线程之synchronized（六）

　　这里学习一下java多线程中的关于synchronized的用法。我来不及认真地年轻，待明白过来时，只能选择认真地老去。

synchronized的简单实例

一、 synchronized在方法上的使用

public class SynchronizedTest {
    public static void main(String[] args) {
        MyThreadB threadB = new MyThreadB();
        new Thread(threadB, "T-1").start();
        new Thread(threadB, "T-2").start();
    }
 
    static class MyThreadB implements Runnable {
        @Override
        public void run() {
            System.out.println(Thread.currentThread().getName() + " before");
            printString();
            System.out.println(Thread.currentThread().getName() + " after");
        }
 
        private synchronized void printString() {
            for (int i = 0; i < 3; i++) {
                try {
                    TimeUnit.SECONDS.sleep(i + 1);
                    System.out.println(Thread.currentThread().getName() + " , i = " + i);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

运行的一次结果如下：

T- before
T- before
T- , i =
T- , i =
T- , i =
T- after
T- , i =
T- , i =
T- , i =
T- after

如果去掉synchronized之后，一次的打印结果如下：

T- before
T- before
T- , i =
T- , i =
T- , i =
T- , i =
T- , i =
T- after
T- , i =
T- after

二、synchronized代码块的使用

public class SynchronizedTest {
    public static void main(String[] args) {
        MyThreadA threadA = new MyThreadA();
        new Thread(threadA, "T-1").start();
        new Thread(threadA, "T-2").start();
    }
 
    static class MyThreadA implements Runnable {
        @Override
        public void run() {
            System.out.println(Thread.currentThread().getName() + " outside of synchronized.");
            synchronized (this) {
                for (int i = 0; i < 3; i++) {
                    try {
                        TimeUnit.SECONDS.sleep(i + 1);
                        System.out.println(Thread.currentThread().getName() + " , i = " + i);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }
}

一次的运行结果如下：

T- outside of synchronized.
T- outside of synchronized.
T- , i =
T- , i =
T- , i =
T- , i =
T- , i =
T- , i = 

如果去掉synchronized之后，一次的打印结果如下：

T- outside of synchronized.
T- outside of synchronized.
T- , i =
T- , i =
T- , i =
T- , i =
T- , i =
T- , i = 

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