Java’s String class provides a rich set of built-in methods for manipulating text. In this post, we demonstrate the most commonly used string functions — including case conversion, length, concatenation, trimming, character access, equality checks, and index searching — through a simple interactive Java program.

String Methods Covered

Java Program: String Manipulation Demo

import java.io.*;

public class StringManipulation {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        // Read two input strings from the user
        System.out.print("Enter first string: ");
        String firstString = reader.readLine();

        System.out.print("Enter second string: ");
        String secondString = reader.readLine();

        // Display the original strings
        System.out.println("\n--- String Information ---");
        System.out.println("First string  : " + firstString);
        System.out.println("Second string : " + secondString);

        // Case conversion
        System.out.println("\n--- Case Conversion ---");
        System.out.println("First string in lowercase  : " + firstString.toLowerCase());
        System.out.println("Second string in uppercase : " + secondString.toUpperCase());

        // Length
        System.out.println("\n--- Length ---");
        System.out.println("Length of first string  : " + firstString.length());
        System.out.println("Length of second string : " + secondString.length());

        // Concatenation
        System.out.println("\n--- Concatenation ---");
        System.out.println("Concatenated string : " + firstString.concat(secondString));

        // Trim (removes leading/trailing whitespace)
        System.out.println("\n--- Trim ---");
        System.out.println("First string after trim : " + firstString.trim());

        // Character access (index 2 = third character, 0-based)
        System.out.println("\n--- Character Access (index 2) ---");
        System.out.println("3rd character of first string  : " + firstString.charAt(2));
        System.out.println("3rd character of second string : " + secondString.charAt(2));

        // Equality checks
        System.out.println("\n--- Equality ---");
        System.out.println("Strings are equal (case-sensitive)  : " + firstString.equals(secondString));
        System.out.println("Strings are equal (ignore case)     : " + firstString.equalsIgnoreCase(secondString));

        // Index of character
        System.out.println("\n--- Index Search ---");
        System.out.println("Index of 'a' in second string : " + secondString.indexOf('a'));
    }
}

How the Code Works

1. Input — Two strings are read from the console using BufferedReader.
2. toLowerCase() / toUpperCase() — Return new string objects with all letters converted; the original string is unchanged (strings are immutable in Java).
3. length() — Returns the number of characters, including spaces and special characters.
4. concat() — Returns a new string with the argument appended to the end. Equivalent to the + operator for strings.
5. trim() — Strips whitespace from both ends. Useful when processing user input that may have accidental spaces.
6. charAt(2) — Returns the character at index 2 (the third character, since indexing starts at 0).
7. equals() — Performs a case-sensitive character-by-character comparison. Returns false if any character differs in case.
8. equalsIgnoreCase() — Same comparison but treats uppercase and lowercase as equal.
9. indexOf(‘a’) — Scans the string left-to-right for the first occurrence of the character 'a'. Returns its index or -1 if not found.

Sample Output

Enter first string: Ankur
Enter second string: Mhatre

--- String Information ---
First string  : Ankur
Second string : Mhatre

--- Case Conversion ---
First string in lowercase  : ankur
Second string in uppercase : MHATRE

--- Length ---
Length of first string  : 5
Length of second string : 6

--- Concatenation ---
Concatenated string : AnkurMhatre

--- Trim ---
First string after trim : Ankur

--- Character Access (index 2) ---
3rd character of first string  : k
3rd character of second string : a

--- Equality ---
Strings are equal (case-sensitive)  : false
Strings are equal (ignore case)     : false

--- Index Search ---
Index of 'a' in second string : 2

Output Explanation

• Lowercase / Uppercase — “Ankur” → “ankur”; “Mhatre” → “MHATRE”.
• charAt(2) — In “Ankur” the characters are A(0) n(1) k(2) u(3) r(4), so index 2 is ‘k’. In “Mhatre”, index 2 is ‘a’.
• equals / equalsIgnoreCase — Both return false because “Ankur” and “Mhatre” are completely different strings.
• indexOf(‘a’) — In “Mhatre”, ‘a’ first appears at index 2 (M=0, h=1, a=2).

See Also

• Implementing Singly Linked List in Java — Another Java data structure implementation
• Implementing Tower of Hanoi Problem in Java — Classic Java recursion example

Conclusion

Java’s String class is one of the most feature-rich classes in the standard library. The methods demonstrated here cover the most common text-processing tasks you’ll encounter in everyday programming. Remember that all string methods in Java return new strings rather than modifying the original, because Java strings are immutable by design.