Java Professional Certification

1. What is the default value of a boolean variable in Java?

false

undefined

null

true

2. Which method is used to start a thread in Java?

start()

run()

begin()

execute()

3. What is the correct way to declare a constant in Java?

final int MAX = 100;

static int MAX = 100;

int MAX = 100;

const int MAX = 100;

4. Which of these is a checked exception in Java?

ArrayIndexOutOfBoundsException

ArithmeticException

NullPointerException

IOException

5. Which keyword is used to inherit a class in Java?

super

extends

implements

inherits

6. What does the hashCode() method in Java return?

An integer representation of the object

The size of the object in bytes

A unique identifier for each object

The memory address of the object

7. Which collection class allows you to access elements using a unique key?

HashSet

HashMap

LinkedList

ArrayList

8. What is the purpose of the final keyword in Java?

To define a variable that cannot be changed

To prevent method overriding

To prevent class inheritance

All of the above

9. What is the default access modifier for a class, method, or variable in Java?

public

private

protected

package-private (default)

10. Which of the following statements is correct about interfaces in Java?

Interfaces can have constructors.

Interfaces can contain static methods with implementations.

Interfaces can contain instance variables.

Interfaces cannot extend other interfaces.

11. What is the output of the following code snippet?

                    
                        String s1 = "hello";
                        String s2 = "hello";
                        System.out.println(s1 == s2);

false

Compilation error

true

Runtime error

12. Which Java feature ensures that objects no longer in use are removed from memory?

Garbage collection

Reference counting

Memory mapping

Automatic variable declaration

13. What will be the result of the following code snippet?

                    
                        int x = 5;
                        int y = 10;
                        System.out.println(x > y ? x : y);

10

Runtime error

Compilation error

5

14. Which of the following is true for a finally block in Java?

It must be placed before the try block.

It always executes after the try block.

It executes only when there is no catch block.

It executes only when an exception is thrown.

15. Which package is imported by default in every Java program?

java.lang

java.net

java.io

java.util

16. Which of the following statements is true about the static keyword in Java?

Static methods can access instance variables.

A static variable is shared among all instances of a class.

Static methods can be overridden.

A static block can only initialize instance variables.

17. What is the base class of all classes in Java?

java.util.Object

java.lang.Class

java.lang.Object

java.util.Class

18. Which statement about Java constructors is true?

A constructor must have the same name as the class.

You cannot have a parameterized constructor in Java.

Constructors can return a value.

Constructors cannot be overloaded.

19. What is the correct syntax for declaring an abstract method in Java?

abstract void myMethod() { }

void myMethod() abstract;

void myMethod();

void myMethod() abstract;