in java, i have created 2 string literals having same value
String a = "Hello";
String b = "Hello";
now both of them should have same reference
System.out.println(a==n); // returns true
but when i do
b+=" World";
System.out.println(a==b); // returns false
Now i have 2 questions here
1. why a and b are not referencing to same object after 'b+=' operation?
2. how come i'm able to change string b without any error?(because i have read String class is immutable)
The reason you can change b is because you're technically making a new String object and assigning it to the existing reference.
b += " World"
is the same as
b = b + " World";
b is technically pointing to a new String object. So to start out, a and b are pointing to the same object, but when b is modified it is now a different object, so a will not equal "Hello World" and a==b will now be false.
For examples of mutable String classes, try StringBuffer or StringBuilder. You can use their .append() method to add to the string, along with other methods to modify it.