Java Class Design Flashcards

Questions and Answers

What types of inheritance does Java support?

Java supports single inheritance.

How do you extend a class in Java?

By using the 'extends' keyword.

How are classes accessed if they are not marked as public?

Only subclasses and classes from the same package can access them.

What do all Java objects implicitly extend from?

java.lang.Object. Signup and view all the answers

What must you ensure when using constructors and inheritance?

The child's constructor and the parent's constructor must match up. Signup and view all the answers

How do you access inherited class members in Java?

You can access them like they're part of your own class. Signup and view all the answers

What happens if you override a method in Java?

The child class method replaces the parent class method. Signup and view all the answers

What are the rules for method overriding in Java?

The method must have the same signature and be at least as accessible. Signup and view all the answers

What is the difference between overriding and method hiding?

Overriding allows dynamic method resolution, while hiding occurs with static methods. Signup and view all the answers

What happens if you create a final method in a parent class?

It cannot be overridden or hidden in a child class. Signup and view all the answers

What can you say about variables in Java inheritance?

Variables can't be overridden but can be hidden. Signup and view all the answers

What is an abstract class in Java?

A class marked with the abstract keyword that cannot be instantiated. Signup and view all the answers

What must the first concrete class extending an abstract class do?

It must implement all abstract methods. Signup and view all the answers

What is an interface in Java?

An abstract data type that defines a list of abstract public methods. Signup and view all the answers

What are the conditions for implementing multiple interfaces?

The methods must have the same signature or differ only in parameters. Signup and view all the answers

What is the default interface method?

A method in an interface marked with the default keyword that has a body. Signup and view all the answers

What should happen if two interfaces with default methods conflict?

The compiler will throw an error. Signup and view all the answers

What must be provided to use a static method in an interface?

A reference to the name of the interface. Signup and view all the answers

What does polymorphism allow in Java?

Accessing a Java object with a reference type that is its own type, a super class, or an interface. Signup and view all the answers

What is required when casting an object from a superclass to a subclass?

An explicit cast is required. Signup and view all the answers

What can you do with polymorphic parameters?

Use a superclass as a parameter for methods with subclass instances. Signup and view all the answers

Study Notes

Inheritance in Java

Java supports single inheritance, allowing a class to inherit from only one parent class, which enhances code clarity.
A class can implement multiple interfaces, allowing for greater flexibility in design.

Extending Classes

The extends keyword is used to indicate a child class deriving from a parent class, granting access to public and protected members.
Constructors in a child class can call parent constructors using super(), with ordering requirements for explicit calls.

Access Modifiers

Public access modifier on a class allows access from any other class; absence of the modifier restricts access to subclasses and classes in the same package.

Object Hierarchy

All Java objects implicitly extend java.lang.Object if they do not extend another class.

Constructor Behavior

The child's constructor must match the parent's constructor signatures if the parent requires arguments.
If not explicitly called, a no-argument constructor is automatically provided by the compiler.

Accessing Members

Public and protected members can be accessed in child classes as if they were defined there, using this. for local context and super. for parent context.

Method Overriding

Non-private parent methods can be overridden in child classes using the same signature and return type; private methods cannot be overridden but can be "shadowed".

Overriding Rules

Overridden method in child must match signature, be equally or more accessible, and conform to exception handling rules of the parent method.

Method vs Variable Behavior

Variables cannot be overridden; they can only be hidden by declaring another variable with the same name in the child class.
For variable reference, super. is used to access parent class variables from child classes.

Abstract Classes and Methods

Abstract classes cannot be instantiated and may contain both abstract and concrete methods, but must implement all abstract methods in the first concrete subclass.

Interfaces Characteristics

Interfaces define methods that implementing classes must provide, allowing classes to implement multiple interfaces for greater functionality.

Rules for Interfaces

Interfaces cannot be instantiated, must have public access, and may not be final. All methods are considered public and abstract unless defined as static.

Default Methods in Interfaces

Introduced in Java 8, default methods allow interfaces to include method bodies, providing backward compatibility while allowing overriding.

Static Methods in Interfaces

Static methods can be defined in interfaces, accessible using InterfaceName.methodName();, and do not conflict across multiple interface implementations.

Polymorphism in Java

Allows objects to be referenced by their own type, a superclass, or an interface type, affecting accessible properties and methods based on the reference type.

Casting in Java

Implicit casting occurs when moving from subclass to superclass, while explicit casting is needed for superclass to subclass.
Runtime exceptions may occur if an object is not an instance of the target type being cast.

Polymorphic Parameters

Methods can use superclass or interface types as parameters, enabling flexibility to accept any subclass instances.

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Description

These flashcards cover essential concepts in Java class design, including types of inheritance and extending classes. Understanding these principles is crucial for effective Java programming and software design. Test your knowledge on how Java handles inheritance and class relationships to enhance your coding skills.