What are immutable objects?

Question

What is the relationship with thread-safety and immutable objects? Does it makes easier to share a single resource among multiple threads? If immutable objects are stateless, can they be pooled in a container like a J2EE container?

thanks

Answer 1

Immutable objects are objects that can not be changed. If an object can not be changed, then there is no concern that a competing thread will change the object state "behind the back" of the executing thread, and therefore immutable objects do not need to be protected via synchronization or some other technique.