Input in Java

Chapter 6

Input in Java

Class 10 - Logix Kips ICSE Computer Applications with BlueJ

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Assignment Questions and Answers

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Question 1

Suppose you want to use the class MyClass of the package MyPackage.UtilityLibrary in a program you are writing. What do you need to do to make the following?

i. class MyClass available to your program

Answer

import MyPackage.UtilityLibrary.MyClass;

ii. all the classes of the package available to your program

Answer

import MyPackage.UtilityLibrary.*;

Question 2

Explain data input technique in a program using the Scanner class.

Answer

The data entered by the user through the keyboard is provided to our Java program with the help of standard input stream that is specified as System.in in the program. We connect our Scanner class to this stream while creating its object. The input received by Scanner class is broken into tokens using a delimiter pattern. The default delimiter is whitespace. Scanner class provides various next methods to read these tokens from the stream. The different next methods provided by Scanner class are next(), nextShort(), nextInt(), nextLong(), nextFloat(), nextDouble(), nextLine(), next().charAt(0).

Question 3

What are delimiters? Which is the default delimiter used in the Scanner class?

Answer

A delimiter is a sequence of one or more characters that separates two tokens. The default delimiter is a whitespace.

Question 4

What are errors in a program?

Answer

Errors are mistakes in a program that prevents it from its normal working. They are often referred to as bugs. Errors are classified into three categories — Syntax Errors, Runtime Errors and Logical Errors.

Question 5

Explain the following terms, giving an example of each.

i. Syntax error

Answer

Syntax Errors are the errors that occur when we violate the rules of writing the statements of the programming language. These errors are reported by the compiler and they prevent the program from executing. For example, the following statement will give an error as we missed terminating it with a semicolon:

int sum

ii. Runtime error

Answer

Errors that occur during the execution of the program primarily due to the state of the program which can only be resolved at runtime are called Run Time errors.
Consider the below example:

import java.util.Scanner; 
class RunTimeError
{   
    public static void main(String args[]) {
          Scanner in = new Scanner(System.in);
          System.out.print("Enter a number: ");
          int n = in.nextInt();
          int result = 100 / n;
          System.out.println("Result = " + result);
      }
}

This program will work fine for all non-zero values of n entered by the user. When the user enters zero, a run-time error will occur as the program is trying to perform an illegal mathematical operation of division by 0. When we are compiling the program, we cannot say if division by 0 error will occur or not. It entirely depends on the state of the program at run-time.

iii. Logical error

Answer

When a program compiles and runs without errors but produces an incorrect result, this type of error is known as logical error. It is caused by a mistake in the program logic which is often due to human error. Logical errors are not caught by the compiler. Consider the below example for finding the perimeter of a rectangle with length 2 and breadth 4:

class RectanglePerimeter{
    public static void main(String args[]) {
        int l = 2, b = 4;
        double perimeter = 2 * (l * b);    // This line has a logical error
        System.out.println("Perimeter = " + perimeter);
     }
 }

Output

Perimeter = 16

The program gives an incorrect perimeter value of 16 as the output due to a logical error. The correct perimeter is 12. We have written the formula of calculating perimeter incorrectly in the line double perimeter = 2 * (l * b);. The correct line should be double perimeter = 2 * (l + b);.

Question 6

If a student forgot to put a closing quotation mark on a string, what kind error would occur?

Answer

Syntax error

Question 7

A program has compiled successfully without any errors. Does this mean the program is error free? Explain.

Answer

Successful compilation of the program only ensures that there are no syntax errors. Runtime and logical errors can still be there in the program so we cannot say that the program is error free. Only after comprehensive testing of the program, we can say that the program is error free.

Question 8

A program needed to read an integer, but the user entered a string instead, and an error occurred when the program was executed. What kind of error is this?

Answer

This is a Runtime error.

Question 9

A student was asked to write a program for computing the area of a rectangle and he, mistakenly, wrote the program to compute the perimeter of a rectangle. What kind of error is this?

Answer

This is a Logical error.

Question 10

What is a java package? Give an example.

Answer

A package is a named collection of Java classes that are grouped on the basis of their functionality. For example, java.util.

Question 11

Explain the use of import statement with an example.

Answer

import statement is used to import built-in and user-defined packages and classes into our Java program. For example, we can import all the classes present in the java.util package into our program using the below statement:

import java.util.*;

Question 12

Distinguish between the following:

i. next() and nextLine()

Answer

 

ii. next() and next().charAt(0)

Answer

 

iii. next() and hasNext()

Answer

 

iv. hasNext() and hasNextLine()

Answer

Question 13

Consider the following input:
    one, two three, four, five

What values will the following code assign to the variables input1 and input2 ?

    String input1 = keyboard.next();
     String input2 = keyboard.next();

Answer

input1 ⇒ one,
input2 ⇒ two

Question 14

Write a line of code that:

i. Creates a Scanner object named scanner to be used for taking keyboard input.

Answer

Scanner scanner = new Scanner(System.in);

ii. Uses the object scanner to read a word from the keyboard and store it in the String variable named stg.

Answer

String stg = scanner.next();

Question 15

Write a code that creates a Scanner object and sets its delimiter to the dollar sign.

Answer

Scanner scanner = new Scanner(System.in);
scanner.useDelimiter("$");

Question 16

Write a statement to let the user enter an integer or a double value from the keyboard.

Answer

Scanner keyboard = new Scanner(System.in);
double num = keyboard.nextDouble();