Why String in immutable?

String class immutable. You can not change its state once after creation.  String str=new String("java"); This line creates object of string "java" . You have again this time str=new String("core"); So be clear that it does not assign this value to the previous object(having "java" value) instead it creates new object and assigns "java" value. Now str will point only new object which we have created recently having "java" value. An object having "core" value is unreachable , it may get garbage collected when gc will run. This is the reason string is called immutable.

Following could be the reason of string immutability :

• Mostly we use string value  parameter to pass to another method.
• Classloader uses string type to load the classes.
• String could cache its own hash code.

These are the reasons which i think , if you know any other please post here