Strings look simple…

But Java Strings hide some very important concepts:

Immutability

String Pool

Memory optimization

And interviewers LOVE asking about them.

What is a String?

A String is a sequence of characters.

In Java:

Strings are objects of the String class.

String name = "Java";

Why Strings Are Immutable

Once a String is created:

Its value cannot be changed.

Example:

String s = "Hello";

s = s + " World";

This creates:

Old object → "Hello"

New object → "Hello World"

The original string remains unchanged.

String Pool Explained

Java stores string literals inside a special memory area called the String Pool.

String s1 = "Hello";

String s2 = "Hello";

Both variables point to the same pooled string.

This saves memory and improves performance.

Important String Methods

String str = " Java DSA ";

str.length();

str.trim();

str.toUpperCase();

str.charAt(2);

str.indexOf("DSA");

str.substring(2, 9);

equals() vs ==

This is one of the most common beginner mistakes.

String a = new…