ICSE Class 10 Computer Applications: Java String Handling Guide

Ever tried to rearrange the letters of a word to make a secret code? In Java, that kind of fun is called string handling.

A string is just a line of text – like a necklace of characters. Java lets you grab, cut, stitch, or compare those necklaces in many ways, all with simple commands.

What is a String in Java?

A String (capital S) is a built‑in object that stores a sequence of characters, such as letters, numbers, or symbols. Think of it as a train where each carriage holds one character. Once you create a string, Java keeps it safe and you can ask it questions or change it without breaking the train.

Creating Strings

You can make a string in two common ways:

String s = "Hello World"; – the text is written directly between double quotes.
String s = new String("Hello World"); – you ask Java to build a new string object using the new keyword.

Both give you a string called s. The first style is shorter and is what most students use in exams.

Common String Methods

Methods are actions you can perform on a string, like tools in a toolbox. Below is a quick cheat‑sheet that shows the most useful ones for ICSE.

Method	What it does	Example
`length()`	Returns the number of characters in the string.	`"Java".length() // 4`
`charAt(int index)`	Gives the character at the specified position (starting at 0).	`"Java".charAt(2) // 'v'`
`substring(int start, int end)`	Extracts part of the string from `start` (inclusive) to `end` (exclusive).	`"Java".substring(1,3) // "av"`
`concat(String str)`	Joins another string to the end of the current one.	`"Hello".concat(" World") // "Hello World"`
`equals(Object obj)`	Checks if two strings have exactly the same characters.	`"abc".equals("ABC") // false`
`compareTo(String another)`	Compares two strings alphabetically; returns 0 if equal, negative if first is smaller, positive if larger.	`"apple".compareTo("banana") // negative`
`toUpperCase()`	Changes every letter to its capital form.	`"Java".toUpperCase() // "JAVA"`
`toLowerCase()`	Changes every letter to its small form.	`"Java".toLowerCase() // "java"`
`trim()`	Removes blank spaces at the beginning and end.	`" hello ".trim() // "hello"`
`replace(char old, char new)`	Swaps every occurrence of `old` with `new`.	`"ball".replace('b','c') // "call"`
`split(String regex)`	Breaks the string into an array using a delimiter (like commas).	`"a,b,c".split(",") // ["a","b","c"]`

Worked Example: Counting Vowels

Suppose the exam asks you to count how many vowels (a, e, i, o, u) are in a sentence. Here’s a clean way using the methods above:

import java.util.Scanner;

public class VowelCount {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a sentence: ");
        String input = sc.nextLine();
        // Step 1: remove extra spaces
        input = input.trim();
        // Step 2: make everything lower case for easy checking
        input = input.toLowerCase();
        int count = 0;
        for (int i = 0; i

Notice how we used trim(), toLowerCase(), length(), and charAt() – all classic string tools.

Typical String Processing Flow

When a question asks you to clean and analyse text, you usually follow a tiny pipeline. The flowchart below shows the usual steps.

graph TD A[Read String] --> B[Trim spaces] B --> C[Convert to lower case] C --> D[Split into words] D --> E[Process each word] E --> F[Display result]

Tips for ICSE Exams

Remember that == checks if two string references point to the same object, not if the text is equal. Use equals() for content comparison.
String objects are immutable – once created, they cannot change. Methods like concat() actually create a new string.
When you need many modifications, consider StringBuilder (but for most ICSE questions, the basic methods are enough).

📝 Likely Exam Questions

Write a program to reverse a string entered by the user.
Model answer: use StringBuilder sb = new StringBuilder(input); sb.reverse(); System.out.println(sb.toString());
Explain the difference between equals() and == for strings.
Model answer: equals() compares the actual characters; == compares memory addresses (whether both references point to the same object).
Given the string " Java Programming ", show the output of trim(), toUpperCase(), and substring(5,13) in that order.
Model answer: After trim() → "Java Programming"; after toUpperCase() → "JAVA PROGRAMMING"; after substring(5,13) → "PROGRAM".
Write a short code snippet to count how many times the word "java" appears in a paragraph (case‑insensitive).
Model answer: Convert paragraph to lower case, use split("java"), then count = parts.length - 1.

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