Java Coding Questions

Given the following class, what’s the output when creating a book with no parameters?

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class Book { String title; Book() { this("Untitled"); System.out.println("Default constructor called"); } Book(String title) { this.title = title; System.out.println("Title constructor called: " + title); } }

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Book b = new Book();

• Only “Default constructor called”

• Only “Title constructor called: Untitled”

• Both lines, in order

• Compilation error

You want to store a list of books borrowed by a user. Which of the following is the most appropriate collection?

• A. HashSet<Book>

• B. ArrayList<Book>

• C. TreeMap<Book>

• D. Vector<Book>

When a user tries to borrow a book that’s not available, a BookNotAvailableException should be thrown. Which is the correct way to define and throw a custom exception?

• A. throw new Exception("Not available");

• B. class BookNotAvailableException extends RuntimeException

• C. throw new BookNotAvailableException(); after defining the class extending Exception

• D. All of the above are correct

What will happen when the following code is executed?

int[] arr = {10, 20, 30}; for (int i = 0; i <= arr.length; i++) { System.out.println(arr[i]); }

• A. Prints all elements successfully

• B. Compiles but throws ArrayIndexOutOfBoundsException at runtime

• C. Compile-time error

• D. Prints garbage values

Which of the following lines will throw a NullPointerException?

String s = null;

• A. if (s == null)

• B. if ("test".equals(s))

• C. if (s.equals("test"))

• D. System.out.println(s)

What is the output of the following code?

boolean flag = false; if (flag = true) { System.out.println("Flag is true"); } else { System.out.println("Flag is false"); }

• A. Flag is true

• B. Flag is false

• C. Compile-time error

• D. Runtime exception

What is the result of the code below?

public class Test { public static void main(String[] args) { return; System.out.println("This won't print"); } }

• A. Code runs normally

• B. Compilation error: unreachable code

• C. Prints the statement

• D. Runtime exception

What happens when the following code runs?

public class Demo { public void greet() { System.out.println("Hello"); } public static void main(String[] args) { greet(); } }

• A. Hello

• B. Compile-time error: non-static method called from static context

• C. Runtime error

• D. Nothing happens

What’s the issue in the following code?

int i = 0; while (i < 5) { System.out.println(i); }

• A. It prints 0 to 4

• B. Infinite loop

• C. Compile-time error

• D. None

public class Test {

public static void main(String[] args) {

String s1 = "Java";

String s2 = new String("Java");

System.out.println(s1 == s2);

}

}

• A. true

• B. false

• C. Compilation error

• D. Runtime error