Partial abstraction in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is partial abstraction in Java?

Partial abstraction means a class has some methods with implementation and some without. It is done using <code>abstract</code> classes that can have both abstract and concrete methods.

beginner

How do you declare an abstract method in Java?

Use the abstract keyword before the method signature and do not provide a body. For example: abstract void display();

beginner

Can you create an object of an abstract class?

No, you cannot create an object of an abstract class directly. You must create a subclass that implements the abstract methods and then create an object of that subclass.

intermediate

Why use partial abstraction instead of full abstraction?

Partial abstraction lets you share common code in the abstract class while forcing subclasses to provide specific details. It helps avoid code duplication and provides a template for subclasses.

beginner

Example of a partial abstraction in Java?

An abstract class Animal with an abstract method sound() and a concrete method sleep(). Subclasses like Dog implement sound().

Which keyword is used to declare a class with partial abstraction in Java?

A abstract

B partial

C interface

D final

The abstract keyword declares a class that can have both abstract and concrete methods.

Can an abstract class have implemented methods?

A Yes, it can have both abstract and concrete methods

B No, all methods must be abstract

C Only static methods can be implemented

D Only private methods can be implemented

Abstract classes can have both abstract methods (without body) and concrete methods (with body).

What happens if a subclass does not implement all abstract methods?

A It will compile without errors

B It becomes a concrete class

C It must be declared abstract

D It automatically implements methods

If a subclass does not implement all abstract methods, it must also be declared abstract.

Which of these is NOT true about partial abstraction?

A It uses abstract classes

B It cannot be instantiated directly

C It allows some methods to have code

D It requires all methods to be abstract

Partial abstraction means some methods have code; not all methods are abstract.

Why might you choose partial abstraction over interfaces?

A Because interfaces cannot have methods

B To provide common method implementations

C To force all methods to be abstract

D To allow object creation of the abstract class

Partial abstraction allows sharing common code in abstract classes, unlike interfaces which traditionally only declare methods.

Explain partial abstraction in Java and how it differs from full abstraction.

Think about classes that have some methods with code and some without.

Describe a simple example of partial abstraction using an abstract class and a subclass.

Use an animal or vehicle example.