String in Java - Complete guide for Beginners

Introduction

In Java, a String is used to store text data.

Example:

String name = "Jay";

Here "Jay" is a String.

Strings are one of the most commonly used data types in Java because almost every application works with text like usernames, emails, messages, passwords, etc.

What is String in Java?

A String is a sequence of characters.

Example:

String word = "Hello";

Characters:

H e l l o
Why String is Important?

Strings are used everywhere:

• Login systems
• Search functionality
• Form inputs
• APIs
• Database values
• Chat applications

Without Strings, handling text is impossible.

How to Create a String?

1. Using String Literal

String s1 = "Hello";

This is the most commonly used way.

Java stores it inside the String Pool.

2. Using new Keyword

String s2 = new String("Hello");

This creates a new object in heap memory.

Difference Between Literal and new Keyword

String Literal	new Keyword
Stored in String Pool	Stored in Heap
Memory efficient	Creates separate object
Faster	Slightly slower

Example:

String a = "Java";
String b = "Java";


System.out.println(a == b);

Output:

true

• Because both refer to the same object.

String a = new String("Java");
String b = new String("Java");

System.out.println(a == b);

Output:

false

• Because two different objects are created.

String is Immutable

Immutable means:

Once a String is created, it cannot be changed.

Example:

String s = "Hello";

s.concat(" World");

System.out.println(s);

Output:

Hello

• Because concat() creates a new object.

Correct way:

s = s.concat(" World");

System.out.println(s);

Output:

Hello World

Important String Methods

length()

Returns total characters.

String s = "Java";

System.out.println(s.length());

Output:

4

charAt()

Gets character by index.

String s = "Java";

System.out.println(s.charAt(1));

Output:

a

toUpperCase()

String s = "java";

System.out.println(s.toUpperCase());

Output:

JAVA

toLowerCase()

String s = "JAVA";

System.out.println(s.toLowerCase());

Output:

java

equals()

Compares values.

String a = "Java";
String b = "Java";

System.out.println(a.equals(b));

Output:

true

equalsIgnoreCase()

Ignores uppercase/lowercase.

String a = "java";
String b = "JAVA";

System.out.println(a.equalsIgnoreCase(b));

Output:

true

contains()

Checks whether text exists.

String s = "Java Programming";

System.out.println(s.contains("Java"));

Output:

true

startsWith()

String s = "Java";

System.out.println(s.startsWith("Ja"));

Output:

true

endsWith()

String s = "Java";

System.out.println(s.endsWith("va"));

Output:

true

replace()

String s = "Java";

System.out.println(s.replace('a', 'o'));

Output:

Jovo

substring()

• Extracts part of String.

String s = "Programming";

System.out.println(s.substring(0, 6));

Output:

Progra

split()

• Splits String into parts.

String s = "Java Python React";

String arr[] = s.split(" ");

for(String word : arr)
{
    System.out.println(word);
}

Output:

Java
Python
React

== vs equals()

==

• Checks memory reference.

equals()

• Checks actual content.

Example:

String a = new String("Java");
String b = new String("Java");

System.out.println(a == b);
System.out.println(a.equals(b));

Output:

false
true
String Pool

Java stores String literals in a special memory area called:

String Constant Pool

Example:

String a = "Java";
String b = "Java";

• Both point to the same object.
• This saves memory.

StringBuilder

Since String is immutable, repeated modifications create many objects.

To solve this, Java provides:

StringBuilder

Example:

StringBuilder sb = new StringBuilder("Hello");

sb.append(" World");

System.out.println(sb);

Output:

Hello World
StringBuffer

Similar to StringBuilder but thread-safe.

StringBuilder	StringBuffer
Faster	Slower
Not synchronized	Synchronized

Common Interview Programs

Reverse String

String s = "Java";

for(int i = s.length()-1; i >= 0; i--)
{
    System.out.print(s.charAt(i));
}

Output:

avaJ

Palindrome String

String s = "madam";
String rev = "";

for(int i = s.length()-1; i >= 0; i--)
{
    rev += s.charAt(i);
}

if(s.equals(rev))
{
    System.out.println("Palindrome");
}
else
{
    System.out.println("Not Palindrome");
}

Output

Palindrome

And so on

Conclusion

String is one of the most important concepts in Java.

To become strong in Java:

• Understand immutability
• Learn String methods
• Practice String programs
• Know String Pool concept
• Learn difference between == and equals()

Mastering Strings will help a lot in:

• Interviews
• Backend Development
• Spring Boot
• Problem Solving
• Real-world Applications