Understanding Java String Immutability and Assignment

Define a String

String s = "abcd";

The variable s stores a reference to a String object; the arrow in the accompanying diagram indicates that the reference is stored.

Assign a Variable to Another Variable

String s2 = s;

The variable s2 holds the same reference value as s , representing the same object.

String Concatenation

s = s.concat("ef");

After concatenation, s now references a newly created String object.

Summary

Once a String object is created in heap memory, it cannot be modified. All methods of the String class return new objects rather than altering the original string.

If a mutable string is needed, use StringBuffer or StringBuilder ; otherwise, many temporary objects will be created, leading to unnecessary garbage‑collection overhead.