Chapter 4

Question 1

What are the shortcut operators for incrementing or decrementing a variable?

Answer 1

++ (increment) and – (decrement).

Question 2

What is the difference between prefix and postfix notation in increment/decrement?

Answer 2

Prefix (++number): Increment/decrement happens before the rest of the expression is evaluated.

Postfix (number++): Increment/decrement happens after the rest of the expression is evaluated.

Question 3

What is the syntax of a while loop in Java?

Answer 3

while (condition) {
statements;
}

Question 4

When does a while loop stop executing?

Answer 4

When the condition becomes false.

Question 5

What is a common mistake that causes infinite loops?

Answer 5

Failing to update the condition variable (e.g., forgetting to decrement x in while (x > 0)).

Question 6

How can a while loop be used for input validation?

Answer 6

while (number < 1 || number > 100) {
System.out.println(“Invalid input!”);
number = keyboard.nextInt();
}

Question 7

What is the syntax of a do-while loop?

Answer 7

do {
statements;
} while (condition);

Question 8

How is a do-while loop different from a while loop?

Answer 8

A do-while loop always executes the body at least once before testing the condition.

Question 9

What is the syntax of a for loop in Java?

Answer 9

for (initialization; test; update) {
statements;
}

Question 10

What are the three sections of a for loop?

Answer 10

Initialization: Initializes the loop control variable(s).

Test: Condition that determines whether the loop runs.

Update: Updates the loop control variable(s).

Question 11

Why should you avoid modifying the control variable inside the body of a for loop?

Answer 11

It makes the code harder to debug and maintain.

Question 12

What happens if you omit all parts of a for loop (e.g., for(;;))?

Answer 12

It creates an infinite loop.

Question 13

Can a for loop initialize and update multiple variables?

Answer 13

Yes, for example:

java
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for (int i = 0, j = 10; i < 5 && j > 5; i++, j–) {
// Loop body
}

Question 14

What does the break statement do in a loop?

Answer 14

It terminates the loop immediately.

Question 15

What does the continue statement do in a loop?

Answer 15

It skips the current iteration and moves to the next iteration.

Question 16

Why should break and continue be avoided?

Answer 16

They make code harder to read and debug.

Question 17

How does a nested loop execute?

Answer 17

The inner loop runs completely for each iteration of the outer loop

Question 18

If there is a nested loop with 10 iterations for both inner and outer loops, how many total iterations occur?

Answer 18

100 iterations.

Question 19

What are the steps to handle files in Java?

Answer 19

Open the file.
Write or read data.
Close the file.

Question 20

How do you write to a file using PrintWriter?

Answer 20

PrintWriter outFile = new PrintWriter(“output.txt”);
outFile.println(“Hello, world!”);
outFile.close();

Question 21

How do you append data to a file without overwriting it?

Answer 21

FileWriter fw = new FileWriter(“output.txt”, true);
PrintWriter outFile = new PrintWriter(fw);
outFile.println(“Additional data”);
outFile.close();

Question 22

How do you handle file paths with backslashes in Windows?

Answer 22

Use \ in string literals:

java
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PrintWriter outFile = new PrintWriter(“C:\folder\file.txt”);

Question 23

How do you avoid exceptions when writing to a file?

Answer 23

Add throws IOException to the method header:

java
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public static void main(String[] args) throws IOException {
PrintWriter outFile = new PrintWriter(“output.txt”);
outFile.close();
}

Question 24

When should you use a while loop?

Answer 24

When the number of iterations is unknown and the loop may not execute at all.

Question 25

When should you use a do-while loop?

Answer 25

When the loop must execute at least once before testing the condition.

Question 26

When should you use a for loop?

Answer 26

When there is a known iteration count or a counting variable.

Question 27

What is a sentinel value, and how is it used in loops?

Answer 27

A special value (e.g., -1) used to signal the end of user input.

Question 28

Why is it bad practice to update the control variable in a loop body?

Answer 28

It complicates code readability and debugging.

Question 29

What is the code to create a Scanner instance for reading keyboard input?

Answer 29

Scanner keyboard = new Scanner(System.in);

Question 30

How do you prompt a user to enter a filename and read it as a string?

Answer 30

System.out.print(“Enter the filename: “);
String filename = keyboard.nextLine();

Question 31

How do you create a File object to represent a file using the filename input by the user?

Answer 31

File file = new File(filename);

Question 32

What code creates a Scanner to read data from a file?

Answer 32

Scanner inputFile = new Scanner(file);

Question 33

What method is used to check if there is more data to read in a file?

Answer 33

The hasNext() method. Example:

java
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while (inputFile.hasNext()) {
String str = inputFile.nextLine();
System.out.println(str);
}

Question 34

How do you close a file after reading from it?

Answer 34

inputFile.close();

Question 35

What exception must be handled or declared when working with files using Scanner?

Answer 35

IOException. Add a throws IOException clause in the method header:

java
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public static void main(String[] args) throws IOException {
// Code here
}

Question 36

What import statement is used to include the Random class in your program?

Answer 36

import java.util.Random;

Question 37

How do you create an instance of the Random class?

Answer 37

Random randomNumbers = new Random();

Question 38

What method generates a random integer within a specific range?

Answer 38

int number = randomNumbers.nextInt(bound);
This generates a number between 0 (inclusive) and bound (exclusive).

Question 39

What method generates a random floating-point number between 0.0 and 1.0?

Answer 39

double number = randomNumbers.nextDouble();

Question 40

What method generates a random boolean value (true or false)?

Answer 40

boolean flag = randomNumbers.nextBoolean();

Question 41

What is a full example of reading from a file using Scanner?

Answer 41

File file = new File(“data.txt”);
Scanner inputFile = new Scanner(file);

while (inputFile.hasNext()) {
String str = inputFile.nextLine();
System.out.println(str);
}

inputFile.close();

Question 42

Why is it important to close a file after reading?

Answer 42

To free system resources and avoid resource leaks.

Question 43

What happens if a file doesn’t exist when creating a Scanner?

Answer 43

An IOException is thrown, and the program must handle it with try-catch or a throws clause.