OPP Revision Unit I & II

What is the main purpose of an abstract class in Java?

• To provide a complete implementation

• To provide partial implementation

• To define a contract for subclasses

• To allow instantiation of objects

Which keyword is used to declare an abstract method?

• abstract

• final

• static

• void

What is the output of the following code? class A { void display() { System.out.println("Hello"); } } A a = new A(); a.display();

• Hello

• Error

• Hello World

• Nothing

Which of the following is true about interfaces in Java?

• Interfaces can be instantiated

• Interfaces can have constructors

• Interfaces can contain instance fields

• Interfaces can extend multiple other interfaces

What is the purpose of the 'super' keyword in Java?

• To define a new class

• To access private members of a class

• To call a method from the parent class

• To create a new instance of a class

What will happen if a subclass does not implement all abstract methods of its superclass?

• The superclass will be ignored

• The subclass will compile successfully

• The subclass must also be declared abstract

• The program will run with errors

Which of the following statements about packages is true?

• Packages are not necessary in Java

• Packages cannot be nested

• Packages help avoid naming conflicts

• Packages can only contain classes

What is the default access modifier for a class in Java if no modifier is specified?

• public

• protected

• private

• default

Which of the following is a characteristic of an abstract class?

• Can be instantiated

• Can have both abstract and concrete methods

• Cannot have constructors

• Cannot have any methods

What is the output of the following code? System.out.println(5 + 3 + " is the result");

• 5 + 3 is the result

• Error

• 53 is the result

• 8 is the result