java线程 同步与锁定

　　

public class Foo {
private int x = 100;
public synchronized int getX(){
    System.out.println("getx"+x);
    return x;
}
public  int  getY(int y){
 synchronized (this) {
  x=x-y;
System.out.println("gety"+x);
 return x;
 }
 
}}

public class MyThread implements Runnable{
    private Foo foo= new Foo();
    public static void main(String[] args) {
        MyThread m = new MyThread();
        Thread ta = new Thread(m,"thread　A");
        Thread tb = new Thread(m,"thread　B");
        ta.start();
        tb.start();
    }
    @Override
    public void run() {
        for (int i = 0; i < 3; i++) {
            this.get(30);
            try {
                Thread.sleep(20);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName()+":"+foo.getX());
        }
    }

    public int get(int y){
        return foo.getY(y);
    }
}

以上代码只有在加锁时才能保证数据的合理性，两个线程用锁来控制对Foode的访问。

要同步静态方法：需要一个用于整个类对象的锁，这个对象就是这个类（XXX.class）

public  int  getY(int y){
synchronized (xxx.class) {
  x=x-y;
System.out.println("gety"+x);
return x;
}