String Handling

Q: Define the String class and state the package it belongs to.

The String class is the built-in Java class whose objects store sequences of characters and whose methods process them. It belongs to `java.lang`, which is imported automatically.

Q: Why is a Java string said to be immutable?

Once a String object is created its characters cannot be changed. Methods such as `toUpperCase()` and `replace()` return a new string and leave the original as it was.

Q: Give the output of `System.out.println("Ans: " + 2 + 3);` and `System.out.println(2 + 3 + " Ans");`.

`Ans: 23` and `5 Ans`. In the first, the string comes first, so each number is joined. In the second, the numbers are added before the string appears.

Q: Differentiate between `length` and `length()`.

`length` is a property of an array that gives the number of elements and is written without brackets. `length()` is a String method that gives the number of characters and is written with brackets.

Q: For `s = "HYDERABAD"`, find `s.indexOf('A')`, `s.lastIndexOf('A')` and `s.charAt(s.length() - 2)`.

The indices are H0 Y1 D2 E3 R4 A5 B6 A7 D8. Therefore `indexOf('A')` returns 5, `lastIndexOf('A')` returns 7, and `charAt(7)` returns `'A'`.

Q: Why should `equals()` be used instead of `==` to compare two strings?

`==` checks whether two variables refer to the same object, while `equals()` checks whether the two strings contain the same characters. Two different objects can hold the same text, so `==` can give `false` for equal strings.

Q: What value does `"CRICKET".compareTo("CRICKETER")` return? Give the reason.

-2. All seven characters of "CRICKET" match the start of "CRICKETER", so the difference of lengths, 7 - 9 = -2, is returned.

Q: What value does `"apple".compareTo("Apple")` return?

32. The first characters differ: `'a'` is 97 and `'A'` is 65, and 97 - 65 = 32.

ICSE Class 10 · Computer Applications · Chapter 8

What this chapter covers

The String class
Length, character access and case methods
Search methods
Comparison methods
Extraction and modification methods
Extracting and modifying the characters of a string
String arrays
Alphabetical order of strings: bubble sort
Alphabetical order of strings: selection sort
Searching for a string: linear search

Key points

A string is a sequence of characters written in double quotes; `String` is a class in `java.lang`, so a String variable holds a reference to an object.
Characters in a string are indexed from 0 to `length() - 1`; an index outside this range causes `StringIndexOutOfBoundsException`.
Strings are immutable: every method that seems to change a string returns a new string, which must be stored or used.
`length()` counts characters; `charAt(n)` returns the character at index `n`; `trim()` removes spaces only at the two ends.
`toUpperCase()` and `toLowerCase()` change only letters; digits and symbols stay the same.
`indexOf(ch)` and `lastIndexOf(ch)` return the first and last positions of a character, or -1 if it is absent.
`startsWith(str)` and `endsWith(str)` return `true` or `false` and are case-sensitive.
Compare string contents with `equals()` or `equalsIgnoreCase()`, never with `==`.
`compareTo()` returns 0 for equal strings, the difference of Unicode values at the first mismatch, or the difference of lengths when one string begins the other; `compareToIgnoreCase()` does the same while ignoring case.
`substring(b, e)` returns characters from index `b` to index `e - 1`, so its length is `e - b`.
`replace(old, new)` replaces every occurrence of a character; `concat(str)` joins a string; `String.valueOf()` turns any type into a string.
String programs build a new result string in a loop using `charAt()`: counting characters, toggling case, reversing, palindromes, Pig Latin and initials.
Bubble sort and selection sort put a String array in alphabetical order by using `compareTo()` in place of `>` or `<`.
Linear search on a String array compares the key with each element using `equals()` or `equalsIgnoreCase()` and reports -1 if it is not found.

Questions answered

Define the String class and state the package it belongs to.

The String class is the built-in Java class whose objects store sequences of characters and whose methods process them. It belongs to `java.lang`, which is imported automatically.

Why is a Java string said to be immutable?

Once a String object is created its characters cannot be changed. Methods such as `toUpperCase()` and `replace()` return a new string and leave the original as it was.

Give the output of `System.out.println("Ans: " + 2 + 3);` and `System.out.println(2 + 3 + " Ans");`.

`Ans: 23` and `5 Ans`. In the first, the string comes first, so each number is joined. In the second, the numbers are added before the string appears.

Differentiate between `length` and `length()`.

`length` is a property of an array that gives the number of elements and is written without brackets. `length()` is a String method that gives the number of characters and is written with brackets.

For `s = "HYDERABAD"`, find `s.indexOf('A')`, `s.lastIndexOf('A')` and `s.charAt(s.length() - 2)`.

The indices are H0 Y1 D2 E3 R4 A5 B6 A7 D8. Therefore `indexOf('A')` returns 5, `lastIndexOf('A')` returns 7, and `charAt(7)` returns `'A'`.

Why should `equals()` be used instead of `==` to compare two strings?

`==` checks whether two variables refer to the same object, while `equals()` checks whether the two strings contain the same characters. Two different objects can hold the same text, so `==` can give `false` for equal strings.

What value does `"CRICKET".compareTo("CRICKETER")` return? Give the reason.

-2. All seven characters of "CRICKET" match the start of "CRICKETER", so the difference of lengths, 7 - 9 = -2, is returned.

What value does `"apple".compareTo("Apple")` return?

32. The first characters differ: `'a'` is 97 and `'A'` is 65, and 97 - 65 = 32.

Past board exam questions

ICSE 2026 board paper · 15 marks

Write a program to accept a word and print the Symbolic of the accepted word. Symbolic word is formed by extracting the characters from the first consonant, then add characters before the first consonant of the accepted word and end with "TR". Example: AIRWAYS Symbolic word is RWAYSAITR BEAUTY Symbolic word is BEAUTYTR

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``` import java.util.Scanner; class Symbolic { public static void main(String args[]) { Scanner sc = new Scanner(System.in); System.out.print("Enter a word: "); String w = sc.next().toUpperCase(); int pos = w.length(); for (int i = 0; i < w.length(); i++) { char ch = w.charAt(i); if (Character.isLetter(ch) && "AEIOU".indexOf(ch) == -1) { pos = i; break; } } String sym = w.substring(pos) + w.substring(0, pos) + "TR"; System.out.println("Symbolic word is " + sym); } } ```

ICSE 2026 board paper · 1 mark

To extract the word NOW from the word "ACKNOWLEDGEMENT", the Java statement "ACKNOWLEDGEMENT".substring(3, ____) is used. Choose the correct number to fill in the blank.

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ICSE 2026 board paper · 1 mark

Assertion (A): The substring() method modifies the original String. Reason (R): The substring() method can extract part of a String starting from a specific index.

(A) is true and (R) is false.
(A) is false and (R) is true.
Both (A) and (R) are true and (R) is the correct explanation of (A).
Both (A) and (R) are true, but (R) is not the correct explanation of (A).

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(A) is false and (R) is true.

ICSE 2026 board paper · 1 mark

``` String a[ ] = {"Atasi", "Aditi", "Anant", "Amit", "Ahana"}; System.out.println(a[1].charAt(1) + "*" + a[2].charAt(2)); ``` The output of the above statement is:

da
d * a
ti
t * i

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d * a

ICSE 2026 board paper · 1 mark

Which of the following String methods returns a negative value?

length()
equals()
compareTo()
charAt()

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compareTo()

ICSE 2026 board paper · 2 marks

Give the output of the following program segment: ``` String S = "GRACIOUS".substring(4); System.out.println(S); System.out.println ("GLAMOROUS".endsWith(S)); ```

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IOUS false ("GRACIOUS".substring(4) gives "IOUS"; "GLAMOROUS" ends with "ROUS", not "IOUS", so endsWith returns false.)

ICSE 2026 board paper · 2 marks

Name the following: (a) The return data type of the method equals(). (b) The String method which has no parameter and returns a String.

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(a) boolean (b) toUpperCase() (also toLowerCase() or trim())

ICSE 2025 board paper · 15 marks

Define a class to accept a String and Print if it is a Super string or not. A String is Super if the number of uppercase letters are equal to the number of lower case letters. [Use Character & String methods only] Example : “COmmITmeNt” Number of Uppercase letters – 5 Number of Lowercase letters – 5 String is a Super String

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import java.util.Scanner; class SuperString { public static void main(String args[]) { Scanner sc = new Scanner(System.in); System.out.print("Enter a string: "); String s = sc.nextLine(); int upper = 0, lower = 0; // counts of uppercase and lowercase letters for (int i = 0; i < s.length(); i++) { char ch = s.charAt(i); if (Character.isUpperCase(ch)) upper++; else if (Character.isLowerCase(ch)) lower++; } System.out.println("Number of Uppercase letters - " + upper); System.out.println("Number of Lowercase letters - " + lower); if …