Developers consider Java one of the most popular programming languages. Despite its age and the rise of Python as an alternative, Java’s stability, and popularity guarantees that the language will be an integral part of development for years to come.
Programmers and developers who want to take full advantage of Java’s functionality should increase their understanding of the language and everything it can do. This greater understanding dovetails nicely with the concept of upskilling. To that end, we present a lesson on Java abstraction methods. This article will help you understand the differences between abstract class vs Java interface, two of the main building blocks of the Java programming language.
Now before we begin with abstract class vs interface java, let’s kick things off with some definitions.
What is Abstraction? A Refresher
The IT world generally defines abstraction as the process of hiding internal details of implementation and only showing essential functionality things to the user. To put it in non-technical terms, you don’t need to know how sausages are made before eating one. You just want to know the steps required to cook it properly. How it got to your plate is unimportant.
Put another way, the abstraction process focused on an automobile means you can see and interact with the steering wheel and gas and brake pedals. You don’t need access to the fuel injection system or the serpentine belt.
There are two different methods of achieving abstraction in Java, and that’s where we are going next to better understand abstract class vs interface Java.
What is an Abstract Class in Java?
An abstract class is defined as a class that’s declared with the “abstract” keyword. It is a collection of common subclass characteristics that should include at least one abstract method. An abstract class can have multiple concrete methods. Programmers using Java 8 and later can also incorporate default and static methods.
An abstract class cannot be instantiated, meaning you cannot create an object with it.
Programmers use abstract class vs interface Java when they need:
- Default functionality for subclasses
- Templates for future specific classes
- Defining a common interface for any subclasses
- Code reusability
Before we begin with the abstract class vs interface in java difference, let us understand more about the interface in Java.
What is an Interface in Java?
An interface is a blueprint used to implement a class. It is a collection of abstract methods and contains no concrete methods, unlike abstract class. However, the interface offers full abstraction in Java, something that abstract classes cannot do.
Like a class, an interface can contain methods and variables, though the declared methods default to abstract.
Interfaces cannot be instantiated, though abstract classes that implement interfaces can.
Programmers use interface when they need:
- To achieve abstraction
- To support a dynamic resolution at run time
- Achieving loose coupling
- Separating a method’s definition from the inheritance’s hierarchy
Now let’s explore the primary differences between abstract class and interface.
What is the Difference Between Abstract Class vs Interface Java?
The best way to quickly and easily compare abstract class vs interface Java is to illustrate the information in a table. So here we go:
|
|
Abstract Class |
Interface |
|
Access Modifiers |
Can have access modifier |
Does not have access modifiers, and everything defined inside is assumed to be a public modifier |
|
Constructors |
Can declare constructors and destructors |
Cannot declare constructors or destructors |
|
Data Fields |
Can have data fields |
Cannot have data fields |
|
Data Member Accessibility |
Can have any type of class member (e.g., public, private, protected) |
Can only have public members, by default |
|
Defining Fields |
Users can define both fields and constants |
Cannot define fields |
|
Extension Limits |
Extends just one class or one abstract class at a time. Can extend another regular (or concrete) class. |
Can extend any number of interfaces. However, it can only extend interfaces. |
|
Implementation Speed |
Faster than the interface |
Interface is slower and requires extra indirection or dereferencing |
|
Instantiation |
Cannot be instantiated, but it can be invoked if main () exist |
Cannot be instantiated, as it is absolutely abstract |
|
Keywords Used |
Abstract keyword used to declare the abstract class. Also, the abstract class can be extended by using the keyword “extends” |
Interface keyword used to declare interface. Also, interface can be implemented by using the keyword “implements” |
|
Methods |
Can have abstract and non-abstract methods. Can have default method implementation |
Can only have abstract methods, though, since Java 8, it can also have static and default methods. Cannot have implementation due to interfaces providing pure abstraction |
|
Multiple Inheritances |
Can have only one abstract class |
Can implement several interfaces |
|
Structure |
Abstract methods only |
Abstract and concrete methods |
|
Variable Types |
Can have final, non-final, static, and non-static variables |
Can only have final and static variables |
|
When It Should Be Used |
Use when several implementations of the same type share common behavior, Additionally, use it if you require a base class. |
Best used when various implementations share only method signature. Also, a good choice when your classes need additional behavior or dependency injection. |
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