Answer:   A string is immutable means you cannot change it after it was created. Any operation that appears to change the string instead returns a new instance whereas when you need a mutable string, such as where you need to change lots of things, you use a StringBuilder which is a buffer of characters that can be changed.

Answer:   String a =”GangBoard”;
String b =”Online Training”
Stirng C = a + b ;
it will create three separate memory in the Heap
Whereas
Stringbuilder s = new stringbuilder();
s.append(“GangBoard”);
s.append(“Online Training”);
//It will create single instance memory in the Heap