Java Interfaces & Abstract Classes Flashcards

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Questions and Answers

What does an interface do?

It defines common behaviors for classes.

Can abstract classes be used to create objects?

False

How do you denote an abstract method?

Using the 'abstract' modifier in the method header.

How are abstract methods and abstract classes denoted in UML?

Using italics. Signup and view all the answers

If a class contains any abstract methods, must it be defined as abstract?

True Signup and view all the answers

Abstract methods must be implemented in the subclass?

True Signup and view all the answers

How are abstract methods defined?

They are left open ended, so the subclass can provide the specific implementation. Signup and view all the answers

What happens if you don't implement all the abstract methods in a subclass?

The subclass then becomes abstract. Signup and view all the answers

Can you create an abstract class that contains non-abstract methods?

True Signup and view all the answers

Can a subclass be abstract even if the superclass is concrete?

True Signup and view all the answers

Since you cannot create an instance of an abstract class, can you use the class as a datatype?

Yes. Signup and view all the answers

An abstract method must be non-static?

True Signup and view all the answers

What's the definition of static?

Belongs to the class. Signup and view all the answers

What is an interface?

A class-like construct that contains only constants and abstract methods. Signup and view all the answers

What modifier is used to indicate an interface?

public interface. Signup and view all the answers

Can you create an instance of an interface using the new operator?

False Signup and view all the answers

What is the syntax for implementing an interface?

public class ClassName extends AnotherClass implements myInterface{} Signup and view all the answers

When a class implements an interface how are the methods used in the subclass?

You must override ALL of them using the same method signature. Signup and view all the answers

What does the Comparable interface do?

Defines the compareTo method for comparing objects. Signup and view all the answers

How many interfaces can a class implement?

1 or more. Signup and view all the answers

Which package is the Comparable interface in?

java.lang. Signup and view all the answers

What is a marker interface?

An empty interface. Signup and view all the answers

A class can extend only 1 object but can implement many interfaces.

True Signup and view all the answers

What class is the clone() method in?

Object. Signup and view all the answers

When can the object.clone method be accessed?

Only when a class implements the Cloneable interface. Signup and view all the answers

Study Notes

Java Interfaces & Abstract Classes

An interface defines common behaviors for classes, containing only constants and abstract methods.
Instantiation of abstract classes is not possible using the new operator; they cannot be instantiated.
Abstract methods are denoted by the abstract modifier in their method header.
In UML, both abstract methods and abstract classes are represented in italics.
Any class that contains abstract methods must be declared as abstract.
Abstract methods must be implemented in the subclass; failure to do so results in the subclass becoming abstract.
Abstract methods allow subclasses to provide specific implementations, as they are left open-ended.
An abstract class can contain non-abstract methods alongside abstract methods.
A subclass can be abstract even if its superclass is concrete.
Although you can't instantiate an abstract class, it can still be used as a datatype, for example: abstractClass[] ac = new abstractClass[];.
Abstract methods must be non-static; static methods indicate some level of functionality.
The term static refers to a class-level attribute or method that does not require an instance of the class.
Syntax to define an interface includes public interface InterfaceName { }.
You cannot instantiate an interface using the new operator.
To implement an interface, the syntax used is public class ClassName extends AnotherClass implements InterfaceName { }.
A class that implements an interface must override all methods in the subclass with the exact same method signatures.
The Comparable interface is utilized for defining the compareTo method that allows for object comparison.
A single class can implement one or more interfaces, but it can only extend one class.
The Comparable interface is part of the java.lang package.
A marker interface is an empty interface that serves to signify certain properties; for instance, Cloneable is a marker interface.
A class can extend only one superclass but can implement multiple interfaces simultaneously.
The clone() method is found in the Object class.
The object.clone method is accessible only when the class implements the Cloneable interface.

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Test your knowledge of Java interfaces and abstract classes with these flashcards. Each card presents key concepts such as definitions, usage, and methods in Java programming. Perfect for anyone looking to reinforce their understanding of object-oriented programming principles.