Java synchronized static methods: lock on object or class

java class static methods synchronized
jbu picture jbu · Jan 13, 2009 · Viewed 98.4k times · Source

The Java documentation says:

It is not possible for two invocations of synchronized methods on the same object to interleave.

What does this mean for a static method? Since a static method has no associated object, will the synchronized keyword lock on the class, instead of the object?

Answer

Cowan picture Cowan · Jan 13, 2009

Just to add a little detail to Oscar's (pleasingly succinct!) answer, the relevant section on the Java Language Specification is 8.4.3.6, 'synchronized Methods':

A synchronized method acquires a monitor (§17.1) before it executes. For a class (static) method, the monitor associated with the Class object for the method's class is used. For an instance method, the monitor associated with this (the object for which the method was invoked) is used.

Related questions

Does static class contain only static method in java?

I have found code in which static class contains methods that are not declared static. Compiler doesn't display any warning. It seems confusing, doesn't it?

Read More
Static nested class in Java, why?

I was looking at the Java code for LinkedList and noticed that it made use of a static nested class, Entry. public class LinkedList<E> ... { ... private static class Entry<E> { ... } } What is the reason for using …

Read More
Java: Static Class?

I have a class full of utility functions. Instantiating an instance of it makes no semantic sense, but I still want to call its methods. What is the best way to deal with this? Static class? Abstract?

Read More