Class 10 Library Classes Mock Test (ICSE)

Topics in Library Classes

• Wrapper classes
• Autoboxing and unboxing
• Character class methods
• Parsing strings to numbers with Integer.parseInt and Double.parseDouble
• Packages and import

Library Classes practice questions with answers

1. Q1Multiple choice·1 mark
   Which method is used to convert a String representation of a decimal number into a primitive double value?

   1. (a)Double.parseDouble()
   2. (b)Float.parseFloat()
   3. (c)Integer.parseInt()
   4. (d)Double.valueOf()
   Show answer and step marks

   1. Correct option: (a) Double.parseDouble()+1

   Answer: (a)
2. Q2Multiple choice·1 mark
   What is autoboxing in Java?

   1. (a)Automatic conversion of a wrapper class object to its primitive type
   2. (b)Manual conversion using the valueOf() method
   3. (c)Automatic conversion of a primitive type to its corresponding wrapper class object
   4. (d)Converting a String to an integer using parseInt()
   Show answer and step marks

   1. Correct option: (c) Automatic conversion of a primitive type to its corresponding wrapper class object+1

   Answer: (c)
3. Q3Multiple choice·1 mark
   What will be the output of the following statement? `System.out.println(Character.isLetter('9'));`

   1. (a)9
   2. (b)false
   3. (c)true
   4. (d)Compilation error
   Show answer and step marks

   1. Correct option: (b) false+1

   Answer: (b)
4. Q4Short answer·2 marks
   What is a wrapper class in Java? State the primitive data types corresponding to the `Integer` and `Character` wrapper classes.
   Show answer and step marks

   1. A wrapper class is a class that wraps (encapsulates) a value of a primitive data type into an object.+1
   2. `Integer` corresponds to `int`.+0.5
   3. `Character` corresponds to `char`.+0.5

   Answer: A wrapper class wraps a primitive type into an object; Integer corresponds to int and Character corresponds to char.
5. Q5Long answer·4 marks
   Write a Java program to accept an integer number using the Scanner class. Store this value in a primitive int variable, perform autoboxing to store it in an Integer wrapper object, unbox it to perform arithmetic addition of $5$, and finally print the updated value using System.out.println.
   Show answer and step marks

   1. `import java.util.Scanner;` with the class and `main` method declared correctly.+1
   2. `Scanner` object created and the integer read into a primitive `int` variable with `nextInt()`.+1
   3. Autoboxing: assigning the primitive to a wrapper object, `Integer boxed = n;`.+0.5
   4. Unboxing: using the wrapper object in arithmetic, `int updated = boxed + 5;`.+0.5
   5. Printing the updated value with `System.out.println` and a message.+1

   Answer: import java.util.Scanner; class BoxingDemo { public static void main(String args[]) { Scanner sc = new Scanner(System.in); System.out.print("Enter an integer: "); int n = sc.nextInt(); Integer boxed = n; int updated = boxed + 5; System.out.println("Updated value = " + updated); } } Here Integer boxed = n; is autoboxing and boxed + 5 unboxes boxed to an int.
6. Q6Long answer·4 marks
   Write a Java program using the `Scanner` class to accept $10$ integer numbers from the user and store them in an `Integer` array, thereby demonstrating **autoboxing**. Then, traverse the array to compute the sum of all the numbers and find the maximum number, thereby demonstrating **unboxing**. Finally, display the calculated sum and the maximum number.
   Show answer and step marks

   1. `import java.util.Scanner;`, the class and `main` declared, and a `Scanner` object created.+0.5
   2. `Integer arr[] = new Integer[10];` filled in a loop with `arr[i] = sc.nextInt();`, the `int` values being autoboxed.+1
   3. Sum: `sum = sum + arr[i];` in a loop, each `Integer` unboxed to `int`.+0.5
   4. Maximum: `max` initialised to `arr[0]` and replaced whenever `arr[i] > max`.+1
   5. Display of the sum.+0.5
   6. Display of the maximum.+0.5

   Answer: import java.util.Scanner; class WrapperArray { public static void main(String args[]) { Scanner sc = new Scanner(System.in); Integer arr[] = new Integer[10]; System.out.println("Enter 10 integers:"); for (int i = 0; i < 10; i++) { arr[i] = sc.nextInt(); } int sum = 0; int max = arr[0]; for (int i = 0; i < 10; i++) { sum = sum + arr[i]; if (arr[i] > max) max = arr[i]; } System.out.println("Sum = " + sum); System.out.println("Maximum = " + max); } }

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