String pool in java

The easiest way of creating a String object is using a string literal:

String str1 = "You cannot change me!";
String str2 = "You cannot change me!";

here str1 and str2 holds the same String literal.

so at the Compile time  java compiler optimizes handling of string literals(and compile-time constant
expressions that evaluate to strings)

so for the above two String str1 and str2 holds the same character sequence so they will be sharing a single string reference .these type of String are said to be "Interned".

The String class maintains a private pool where such strings are interned.

and if you call any methods on str2 wont effect the str1 reference.

String str3 = "You cannot" + "change me!";

this intern can be applied to str3 also

String s = "change me!";

String str5 = "You cannot" + s ;

 intern will not be applied to str5 so a new string will be created for str5.

and finally A string constructed with new operator will always creates a new reference in jvm.