Class variable: public access read-only, but private access r/w

Question

In my current project I have a class which stores its Instance in a variable. This Instance should be accesible by all other classes in the project, but it may only be altered by its own class.

How can I achieve this?

Answer 1

Write a public getter but no public setter. And the field itself private

Answer 2

In short that is called immutable object, state of Object cannot change after it is constructed.

String is a common example of immutable Class.

Make a class immutable by following-

• ensure the class cannot be overridden - make the class final, or use static factories and keep constructors private.
• make fields private and final
• force callers to construct an object completely in a single step, instead of using a no-argument constructor combined with subsequent calls to setXXX methods.
• do not provide any methods which can change the state of the object in any way - not just setXXX methods, but any method which can change state
• if the class has any mutable object fields, then they must be defensively copied when passed between the class and its caller.