Immutability must be familiar to every one when we talk about String & StringBuffer classes in java. Strings are considered immutable because the values contained in the reference variable cannot be changed. Whereas String Buffer is considered mutable because the value in a string buffer can be changed (i.e. mutable). However I always thought how to make our user defined classes as immutable though I am unaware as to why any one would need this. The reason perhaps might be clear once we have a look at the code. Now in order to make a class immutable we must restrict changing the state of the class object by any means. This in turn means avoiding an assignment to a variable. We can achieve this through a final modifier. To further restrict the access we can use a private access modifier. Above do not provide any method where we modify the instance variables.
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