String is immutable whether We create object or not

Hi,

I have taken a one string and did not create a object of String API. Then I did concatination for the string after concantination I am printing the value

of original string then its returning me a orininal value. 

So question is whether we create object of string or not we can not alter the value of string. In video you said that once object is created we can not alter the value of string.

Please clarify more.