Use of Mutability in Java

An immutable class is a class whose state cannot be changed. This can be done in three ways.

• Private: If a field is private, it cannot be externally changed. If it's a final, you cannot accidentally change it. 
• Do not provide the setter: In support to the earlier point, if the fields are private and no setter is provided, this class fields always remain the same. 
• Declare as final: Sub-classes should not be able to override the methods. 

Pro's:

• Immutable objects can make life easier. An immutable object is automatically thread-safe, and it has no synchronization issues. They make concurrent programming safer and cleaner.
• Immutable objects do not need a copy constructor or an implementation of clone. For the sake of simplicity.
• When an immutable object throws any exception, it will never result with the object left in an indeterminate state. - atomicity by Joshua Bloch in Effective Java

Con's:

• Making copies of objects in order to mutate them can drain our resources, especially when dealing with complex data structures. Also, changing objects with a distinct identity can be also more intuitive.

In Effective Java, Joshua Block writes:
“Classes should be immutable unless there’s a very good reason to make them mutable. If a class cannot be made immutable, limit its mutability as much as possible.”


Immutability can solve many problems and make your life easier, especially when it comes to working in a concurrent environment.