Java Object Oriented Design - Java Immutable Objects

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An object whose state cannot be changed after it is created is called an immutable object.

A class whose objects are immutable is called an immutable class.

An immutable object can be shared by different areas of a program without worrying about its state changes.

An immutable object is inherently thread-safe.

Example

The following code creates an Example of an Immutable Class.

public  class  IntWrapper {
    private  final  int  value;
/*from w  w w.j  ava2 s  . c  o m*/
    public IntWrapper(int value) {
        this.value = value;
    }
    public int  getValue() {
        return value;
    }
}

Note

This is how you create an object of the IntWrapper class:

IntWrapper wrapper  = new IntWrapper(101);

At this point, the wrapper object holds 101 and there is no way to change it.

Therefore, the IntWrapper class is an immutable class and its objects are immutable objects.

It is good practice to declare all instance variables final so the Java compiler will enforce the immutability during compile time.

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