Immutable strings in Java

Strings are said to be immutable in Java.Immutability refers to ability toprevent change in value.
It means whenever you change the value of String, you create a new object and make that variable refer to new object.Appending a string is also a same kind of operation internally.

Each time you use "+" operator or ( String.concat() ) , a new string is created, old data is copied and new data is appended. Old string will be garbage collected.

When to use "+":

1). Multiline Strings

  

String text=
    "line a\n"+
    "line l\n"+
    "line b";

2) Short messages

System.out.println("x:"+x+" y:"+y); 

When you have multiple string blocks to concat use StringBuilder or 

StringBuffer( if multithreading is used ) class.