1.Synchronized
synchronized是Java中解决并发问题的一种最常见也是最简单的方法。synchrinzed的作用主要作用有三个：
（1）确保线程互斥的访问同步代码
（2）保证共享变量的修改能够及时看到
（3）有效解决重排序问题
synchronized总共有三个作用：
（1）修饰普通方法
（2）修饰静态方法
（3）修饰代码块
1.没有同步块的情况
public class SynchronizedTest {
public static void main(String[] args) {
final SynchronizedTest test =new SynchronizedTest();
new Thread(new Runnable() {
@Override
public void run() {
test.methodOne();
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
test.methodTwo();
}
}).start();
}
public void methodOne() {
System.out.println("Method One start");
try {
System.out.println("Method One execute");
Thread.sleep(3000);
}catch (Exception e) {
e.printStackTrace();
}
System.out.println("Method One end");
}
public void methodTwo() {
System.out.println("Method Two start");
try {
System.out.println("Method Two execute");
Thread.sleep(1000);
}catch (Exception e) {
e.printStackTrace();
}
System.out.println("Method Two end");
}
}
执行结果：
Method One start
Method One execute
Method Two start
Method Two execute
Method Two end
Method One end
Process finished with exit code 0
2.对普通方法使用synchronized修饰同步
public class SynchronizedTest {
public static void main(String[] args) {
final SynchronizedTest test =new SynchronizedTest();
new Thread(new Runnable() {
@Override
public void run() {
test.methodOne();
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
test.methodTwo();
}
}).start();
}
public synchronized void methodOne() {
System.out.println("Method One start");
try {
System.out.println("Method One execute");
Thread.sleep(3000);
}catch (Exception e) {
e.printStackTrace();
}
System.out.println("Method One end");
}
public synchronized void methodTwo() {
System.out.println("Method Two start");
try {
System.out.println("Method Two execute");
Thread.sleep(1000);
}catch (Exception e) {
e.printStackTrace();
}
System.out.println("Method Two end");
}
}
执行结果：
Method One start
Method One execute
Method One end
Method Two start
Method Two execute
Method Two end
Process finished with exit code 0
3.使用synchronized修饰静态方法