Why string is called immutable in java?

Why string is called immutable in java?

References

Reference NO 1

http://stackoverflow.com/questions/15198735/why-string-is-called-immutable-in-java

Reference NO 2

http://stackoverflow.com/questions/279507/what-is-meant-by-immutable

Reference NO 3

http://javarevisited.blogspot.com/2010/10/why-string-is-immutable-in-java.html

Reference NO 4

http://www.coderanch.com/t/522391/java-programmer-SCJP/certification/String-class-immutable

Reference NO 5

http://www.careercup.com/question?id=12215810

Reference NO 6

http://en.wikipedia.org/wiki/Immutable_object

Reference NO 7

http://javapapers.com/core-java/java-string/

Reference NO 8

http://java.about.com/od/i/g/immutable.htm