Difference Between Abstract Class and Interface in Java

The only methods interfaces could define were abstract ones or methods without implementation. Therefore, it was not a problem if a class implemented several interfaces with the same method signature.

Interfaces and abstract classes are related concepts. They are not instantiable and may comprise a mixture of methods that have been declared but have not yet been implemented. 

The ability to declare non-static and final fields and public, protected, and private concrete methods are only available with abstract classes. A static method can neither be overridden nor implemented in a child class since it is a characteristic of the class rather than the object instance. Making a static method more abstract is, therefore, useless.

Java Abstract classes are capable of implementing interfaces even in the absence of interface methods. Java Abstract classes are utilized to give all subclasses’ default or common method implementation. Although there is a single superclass limit for Java classes, they can implement several interfaces. Because of this, a class with a separate superclass can implement interfaces but not extend other abstract classes. Interfaces are a more adaptable method of exposing a shared interface and other as well.

The term interface is used to declare an interface which only contains abstract methods that cannot be implemented. Java’s abstract keyword is used to create abstract classes when declaring the class. For classes and methods, the abstract keyword is a non-access modifier. Objects cannot be created using an abstract class, which is a constrained class. An abstract method do not have a form and can only be used in an abstract class.

In contrast to interfaces, which can only extend other interfaces, abstract classes can implement other classes and extend abstract interfaces. Although an interface cannot implement the main method, we can run an abstract class if it contains a main () function.