Inheritance in Java Flashcards

Inheritance Principles

• Private fields and methods of the superclass are not inherited by the subclass.
• If a subclass constructor does not call a superclass constructor, Java automatically invokes the superclass's default (no-arg) constructor.
• Methods can be both overloaded and overridden in subclasses—overloading occurs when methods share the same name but differ in parameters.

Concepts in Object-Oriented Design

• The term "has a" relates to the concept of aggregation, indicating a whole-part relationship.
• The term "is a" relates to inheritance, illustrating a hierarchical relationship between classes.
• When a subclass inherits fields and methods from a superclass, they are not physically included in the subclass's memory.

Relation Indicators

• The keyword extends signifies that a subclass inherits from a superclass.
• In UML diagrams, inheritance is represented with an open arrowhead pointing from the subclass to the superclass.

Object Creation and Constructors

• A subclass can be seen as a specialized version of the superclass, inheriting its properties and behaviors.
• When a new object of a subclass is created, the superclass's constructor is executed before the subclass's constructor.
• If a superclass has a private field (e.g., numHours), it cannot be accessed directly by the subclass.
• Superclass constructors are not inherited by subclasses; each subclass must invoke the superclass constructor if needed.

Default Constructor and Overriding

• The superclass's default constructor is executed first when a subclass is instantiated.
• If a superclass lacks a default no-arg constructor, all subclass constructors must explicitly call a constructor from the superclass.
• The super keyword is essential for invoking the superclass's constructor and accessing its members.

Access Modifiers and Method Overriding

• Protected members are accessible by methods in the subclass and methods within the same package, ensuring controlled access.
• In UML, a protected member is denoted with a #.
• To prevent a method from being overridden in a subclass, use the final modifier in the superclass method definition.

Object Class and Static Members

• All classes in Java inherit from the Object class, which provides fundamental methods like toString and equals.
• Every class has a toString and equals method because they inherit from the Object class.
• Static members belong to a class and cannot be overridden by subclasses, as they are not tied to instances.

Test your knowledge of inheritance in Java with these flashcards. Covering key concepts such as visibility of fields and automatic constructor calls, these flashcards are perfect for anyone needing a refresher on Java inheritance principles.