When to use java abstract class and interface?

In java abstraction, we have the option of using either abstract classes or interfaces. Each has its own advantages and disadvantages, and the choice of which one to use depends on your specific requirements. In this tutorial, we will discuss when to use an abstract class and when to use an interface in Java. Let’s give it a go together:

When to Use an Abstract Class

An abstract class is a class that cannot be instantiated and can only be used as a superclass for other classes. Abstract classes can contain both abstract and non-abstract methods, as well as instance variables. Here are some scenarios where you would want to use an abstract class:

  1. When you want to provide a default implementation: If you have a set of classes that share a common implementation for some methods, you can define those methods in an abstract class. Subclasses can then inherit those methods and override them if necessary.
  2. When you want to enforce a contract: You can use an abstract class to define a contract that subclasses must adhere to. This can include things like required instance variables, required methods, or even a set of constraints that subclasses must satisfy.
  3. When you want to add new methods in the future: If you anticipate adding new methods in the future, an abstract class can be a good choice since you can add non-abstract methods to the class without breaking existing code. Subclasses can choose to override these new methods or inherit the implementation from the superclass.

When to Use an Interface

An interface is a contract that specifies a set of methods that a class must implement. Interfaces cannot have instance variables, and all methods are implicitly public. Here are some scenarios where you would want to use an interface:

  1. When you want to define a contract: Interfaces are useful when you want to define a set of methods that a class must implement. This is useful when multiple classes perform a similar function but have different implementations.
  2. When you want to achieve multiple inheritance: Java does not allow a class to inherit from multiple classes, but it does allow a class to implement multiple interfaces. This is useful when you have a set of methods that are not related to each other by inheritance but are related by function.
  3. When you want to decouple implementation from the definition: Interfaces allow you to separate the definition of a set of methods from their implementation. This can be useful when providing multiple implementations for a single interface.
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Also, see the example code JavaExamples_NoteArena in our GitHub repository. See complete examples in our GitHub repositories.