Kingamere Kingamere - 1 year ago 115
Java Question

Java acquire monitor lock of other class

Let's say I have this class:

public class Status {
private int x;

// monitor lock?
public Object myLock = new Object();

public Status(int x) {
this.x = x;

public int checkVar() {
return x;

public int incrementVar() {

Then I have a thread class like this:

public class MyThread implements Runnable {

public void run() {
// Is this how to acquire monitor lock of Status class?
synchronized (statusInstance.myLock) {

This is how you acquire the monitor lock of another class right?

Answer Source

In Java if you have a reference to any object you can use it as a mutex. But you would be locking on the object and not the class.

The problem is that anyone can mutate that object because it is public and obtain a lock they shouldn't be acquiring.

 statusInstance.myLock = new Object();

Using public mutable objects as mutexes is considered harmful. You can lock on the class given there is only one class in the ClassLoader


Or making your lock static final

public static final Object MY_LOCK = new Object();    
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