静态方法内的同步块将获取类级别锁或对象级别锁

Question

在下面的代码片段中，我有一个问题。线程将获取类级别锁或对象级别锁？

private static Object lock=new Object();
private static Object lock2=new Object();

public static void m1(){
synchronized(lock){
//statements
}
}

public static void m2(){
synchronized(lock2){
//statements
}
}

Answer 1

每个对象都有一个“监视器”。使用同步块时，请指定要在其上同步其监视器的实例。除了同步的块，还有同步的方法。同步的[[instance方法将获取该方法在其上被调用的实例的监视器，而同步的[[static方法将获取该封闭类的java.lang.Class对象的监视器。]

public class Foo {

  private static final Object STATIC_LOCK = new Object();
  private final Object instanceLock = new Object();

  public static void bar() {
    synchronized (STATIC_LOCK) { // acquires monitor of "STATIC_LOCK" instance
      // guarded code
    }
  }

  public static synchronized void baz() { // acquires monitor of "Foo.class" instance
    // guarded code
  }

  public void qux() {
    synchronized (instanceLock) { // acquires monitor of "instanceLock" instance
      // guarded code
    }
  }

  public synchronized void quux() { // acquires monitor of "this" instance
    // guarded code
  }
}

Answer 2

monitor

Answer 3

public class Test {
private static Object lock2 = new Object();

public synchronized void m1() { 
// Lock on current object instance(this) as this is an instance method
}
public synchronized static void m2() { 
    // Lock at class level as this is a static method
 }
public static void m3() {

    synchronized (lock2) { 
        // Lock on `lock2` object. It doesn't make a difference if this method 
        // is static or not at the time of acquiring lock on a given object here
    }
}

}