OOP Concepts and UML

Abstract Classes

• The keyword abstract is used to declare a class as abstract.
• An abstract class cannot have objects created from it.
• It is not necessary for a derived class to implement all the abstract methods of the base class.

Interfaces

• Default methods in Java interfaces allow adding new functionality to an interface without breaking the implementing classes.
• An interface can be extended by another interface.
• Multiple interfaces can be implemented by a class using the implements keyword, separated by commas.

Class Relationships

• The strongest relationship that can exist among the Bank, Account, and Customer classes in a Java program is composition.
• A derived class can extend the Bank class and override its getRateOfInterest() method.
• The classes that should implement the Account interface in a Java banking system program are those that represent types of accounts.

Object-Oriented Programming

• Dependency in object-oriented programming is a relationship where one class uses another class.
• The «creates» stereotype indicates a creation relationship in an association relationship.
• Aggregation is a relationship where one class contains a collection of another class, while composition is a relationship where one class owns a collection of another class.
• The purpose of extending an interface is to add new functionality or to create a new interface that is a modified version of the original interface.

Keywords

• The keyword final is used to declare a class as final in Java.
• Interfaces in Java cannot have instances created from them, and all methods are abstract.
• The implements keyword is used to implement one or more interfaces in a class.
• The correct syntax to implement multiple interfaces in Java is class MyClass implements Interface1, Interface2, ....
• The keyword abstract is used to declare a class as abstract in Java.
• Abstract classes can have constructors.

Methods

• The purpose of an abstract method in a superclass is to provide a blueprint for a method that must be implemented by its subclasses.
• Default methods in Java interfaces allow adding new functionality to an interface without breaking the implementing classes.
• Final methods in Java cannot be overridden by subclasses.

Inheritance

• Inheritance in object-oriented programming is a mechanism of creating a new class from an existing class.

Interfaces

• The purpose of interfaces in Java is to define a contract that must be implemented by any class that implements it.