Input in Java ICSE Class 10 Computer Applications

What Input in Java is about

Weightage: CISCE publishes no chapter weightage. Section A (40 marks) is compulsory: 1-mark MCQs and 2-mark short answers including output and error questions; in Section B you answer any four of six 15-mark programming questions written in Java.Source: CISCE ICSE Computer Applications (661) specimen paper structure for 2027

Key concepts

Three ways to give data to a program

(1) Initialisation: data is written in the program itself before execution: int a = 10; double rate = 8.5; The values are fixed unless the program is edited.

(2) Parameters (arguments): data is supplied at the time of execution, when the method is called. In BlueJ, if main is written as void main(int a, int b), a dialog box asks for a and b when you run it.
class Add
{
void main(int a, int b)
{
System.out.println("Sum = " + (a + b));
}
}
Running with 6 and 9 prints Sum = 15.

(3) Input stream: data is entered by the user during execution, through the keyboard, using the Scanner class: the program pauses, the user types, and the value is read.

Worked example

(2 marks) Distinguish between initialisation and input through Scanner.

Try it first, then show the solutionSolution

1. Initialisation: values are fixed in the program before execution - 1 mark.
2. Scanner: values are entered by the user during execution, so the program works for any data - 1 mark.

Answer: In initialisation the data is written into the program before it runs (int a = 10;), so it is the same every time; with Scanner the user enters data during execution, so the program can work on different values each time.

Packages and the Scanner class

A package is a group of related classes. java.lang is the default package, imported automatically; it contains System, String, Math and the wrapper classes such as Integer and Character. java.util contains utility classes such as Scanner, and must be imported: import java.util.Scanner; (or import java.util.*;) at the top of the program, before the class.

Creating a Scanner object linked to the keyboard:
Scanner sc = new Scanner(System.in);

Methods (as listed in the syllabus):
nextShort() - short; nextInt() - int; nextLong() - long; nextFloat() - float; nextDouble() - double;
next() - one word (up to a space);
nextLine() - a whole line including spaces;
next().charAt(0) - one character (the first character of the next word).

Prompt the user before reading: System.out.print("Enter age: "); int age = sc.nextInt();

Worked example

(2 marks) Write statements to accept a full name with spaces and a grade letter.

Try it first, then show the solutionSolution

1. String name = sc.nextLine(); reads the whole line including spaces - 1 mark.
2. char grade = sc.next().charAt(0); reads one character - 1 mark.

Answer: String name = sc.nextLine();
char grade = sc.next().charAt(0);

next() vs nextLine() and a common trap

next() reads characters up to the next space, so for the input 'Ravi Kumar' it returns only Ravi. nextLine() reads the rest of the line, so it returns Ravi Kumar.

Trap: after nextInt() or nextDouble(), the Enter key's line break is left in the input. A nextLine() called next will read that empty remainder and return "". Solutions: read the String first, or add an extra sc.nextLine(); to clear the line before reading the String.

Example:
int age = sc.nextInt();
sc.nextLine();
String city = sc.nextLine();

Worked example

(2 marks) The user types Neha Sharma. What do next() and nextLine() each return if called first?

Try it first, then show the solutionSolution

1. next() stops at the space: Neha - 1 mark.
2. nextLine() reads the whole line: Neha Sharma - 1 mark.

Answer: next() returns "Neha"; nextLine() returns "Neha Sharma".

Types of errors

(1) Syntax (compile-time) errors: breaking the grammar rules of Java, found by the compiler; the program does not compile. Examples: missing semicolon, misspelt keyword (Int), undeclared variable, mismatched brackets, assigning a double to an int without a cast, using a local variable before giving it a value.

(2) Runtime errors: the program compiles but stops abnormally while running. Examples: dividing an integer by zero (ArithmeticException), using an array index outside its range, entering text when nextInt() expects a number (InputMismatchException).

(3) Logical errors: the program compiles and runs but gives a wrong result because the logic is wrong. Examples: using + instead of *, the wrong formula, a wrong loop condition, 1 / 2 giving 0 in an expression.

Note: in the 2025 cone program, a = 22.0/7*r*l; came before l was given a value. A local variable must be assigned before use, so the compiler rejects it: a syntax (compile-time) error, not a logical error.

Worked example

(2 marks) Identify the type of error: (a) int x = 10 / 0; (b) area = l + b; for the area of a rectangle.

Try it first, then show the solutionSolution

1. (a) Compiles but crashes on execution (division by zero): runtime error - 1 mark.
2. (b) Runs but gives a wrong answer (should be l * b): logical error - 1 mark.

Answer: (a) Runtime error (ArithmeticException: / by zero). (b) Logical error.

Comments

Comments are notes in a program that the compiler ignores; they explain the code to readers.
Single-line comment: starts with // and runs to the end of the line.
// calculate the total
Multi-line comment: starts with /* and ends with */ and can span several lines.
/* This program accepts marks
and prints the average */
(A documentation comment /** ... */ is also used for documentation.)

Good comments, together with a variable description table, help the examiner follow a Section B answer.

Worked example

(1 mark) Which is a valid multi-line comment?
(a) // text //
(b) /* text */
(c) <!-- text -->
(d) text

Try it first, then show the solutionSolution

1. Multi-line comments use /* to start and */ to end.

Answer: (b) /* text */

Input in Java in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Scanner Methods for Reading Values
• Types of Errors and Comments in Java

Input in Java: syntax and key facts

Scanner set-up

import java.util.Scanner; … Scanner sc = new Scanner(System.in);

Import before the class.

Scanner methods

nextShort, nextInt, nextLong, nextFloat, nextDouble, next(), nextLine(), next().charAt(0)

next(): one word; nextLine(): whole line.

Errors

Syntax: compiler rejects; Runtime: crashes while running; Logical: wrong output

Comments

// single line; /* multi-line */

Ignored by the compiler.

How the board asks Input in Java

The question patterns to expect, and the method that works for each.

Tricks to remember Input in Java

Short memory aids. Say each one aloud once, then use it on a question the same day.

• util for input

  Scanner is a utility: java.util. Everything basic (System, Math, String, wrappers) is in java.lang.

  Use it when: Package questions.

• S-R-L

  Syntax stops compiling, Runtime stops running, Logic stops being right.

  Use it when: Types of errors.

Input in Java: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section B style)

Read the situation, then answer every part. In the board paper this is a 10-mark question split into 2 + 3 + 5 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Input in Java

The slips examiners see most often, and what to write instead.

• ✗Mistake: Unable to accept String and char input

  The 2024 examiners reported this in the courier program.

  ✓Do this: String: sc.nextLine() or sc.next(); char: sc.next().charAt(0).

  Usually costs: 1 to 2 marks of 15.

• ✗Mistake: Initialising data instead of accepting it

  In 2024 (EvenPal) and 2025 (Super string) candidates used sample values instead of accepting input.

  ✓Do this: If the question says 'accept', read with Scanner.

  Usually costs: 1 to 2 marks.

• ✗Mistake: Calling a compile-time error logical

  The 2025 examiners noted candidates called the cone program's error logical.

  ✓Do this: If the compiler would refuse the code, it is a syntax (compile-time) error.

  Usually costs: 1 mark.

• ✗Mistake: Forgetting import java.util.Scanner

  Without it, Scanner is an unknown class.

  ✓Do this: Write the import as the first line of every program that uses Scanner.

  Usually costs: 1 mark.

Practice questions on Input in Java

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   Which method reads a whole line including spaces?
   (a) next()
   (b) nextLine()
   (c) nextInt()
   (d) charAt()

   Hint

   Line.

   Answer

   (b) nextLine()

2. Q2 · 1 mark · MCQBoard level

   Scanner belongs to the package:
   (a) java.lang
   (b) java.util
   (c) java.io only
   (d) java.math

   Hint

   Utility.

   Answer

   (b) java.util

3. Q3 · 1 mark · MCQBoard level

   Dividing an integer by zero causes a:
   (a) syntax error
   (b) logical error
   (c) runtime error
   (d) comment

   Hint

   While running.

   Answer

   (c) runtime error

4. Q4 · 2 marks · Very short answerBoard level

   Distinguish between a syntax error and a logical error with an example each.

   Hint

   Compile vs result.

   Answer

   A syntax error breaks Java's rules and is caught by the compiler, e.g. a missing semicolon. A logical error lets the program run but gives wrong output, e.g. writing area = l + b; instead of l * b.

5. Q5 · 2 marks · Very short answerHarder board level

   Write statements to accept a long phone number and a float weight.

   Hint

   nextLong, nextFloat.

   Answer

   long phone = sc.nextLong();
   float weight = sc.nextFloat();

6. Q6 · 2 marks · Short answerHOTS / competency

   The user types: 25 Delhi Public School. What do these give, in order? int a = sc.nextInt(); String s = sc.next(); String t = sc.nextLine();

   Hint

   next stops at space.

   Answer

   a = 25; s = "Delhi"; t = " Public School" (the rest of the line, starting with the space).

7. Q7 · 2 marks · Very short answerHarder board level

   Why is java.lang not imported in programs, while java.util is?

   Hint

   Default.

   Answer

   java.lang is imported automatically into every Java program because it holds essential classes (System, String, Math, wrappers); other packages such as java.util must be imported explicitly.

8. Q8 · 15 marks · Long answerBoard level

   Write a program to accept the length of a side of a square and its unit as a word (e.g. cm), and print the area and perimeter with the unit.

   Hint

   next() for the unit.

   Answer

   import java.util.Scanner;
   class Square
   {
   public static void main(String args[])
   {
   Scanner sc = new Scanner(System.in);
   System.out.print("Side: ");
   double s = sc.nextDouble();
   System.out.print("Unit: ");
   String u = sc.next();
   System.out.println("Area = " + (s * s) + " sq " + u);
   System.out.println("Perimeter = " + (4 * s) + " " + u);
   }
   }
   Trace with 6 and cm: Area = 36.0 sq cm; Perimeter = 24.0 cm.

9. Q9 · 2 marks · Short answerHOTS / competency

   A program prints the average of 5 and 6 as 5. Name the error type and explain a likely cause.

   Hint

   int division.

   Answer

   A logical error: the average was probably computed as (a + b) / 2 with int variables, so 11 / 2 gave 5. Use (a + b) / 2.0 to get 5.5.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Default package of Java?Show answer

   java.lang

2. 2.Read one character?Show answer

   sc.next().charAt(0)

3. 3.Error caught by the compiler?Show answer

   Syntax (compile-time) error.

4. 4.Single-line comment symbol?Show answer

   //

5. 5.Three ways of giving data?Show answer

   Initialisation, parameters, input stream (Scanner).

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Initialisation: before execution; parameter: at execution; Scanner: during execution.
• ☐import java.util.Scanner; Scanner sc = new Scanner(System.in);
• ☐nextInt, nextDouble, nextLong, nextShort, nextFloat, next, nextLine, next().charAt(0).
• ☐Syntax error: won't compile; runtime: crashes; logical: wrong output.
• ☐// one line; /* many lines */

Input in Java: frequently asked questions