Difference between Interface and Abstract class in Java?

Both interfaces and abstract classes are used to provide abstraction in Java, but there are some key differences between them:

Implementation: An interface is a pure abstraction that only specifies the methods that must be implemented by a class that implements the interface. An abstract class, on the other hand, can provide a partial implementation by defining methods that can be used by concrete subclasses.
Inheritance: A class can implement multiple interfaces, but it can only extend one abstract class. This is because Java supports multiple interface inheritance, but not multiple class inheritance.
Accessibility: Interface methods are implicitly public and abstract, whereas abstract class methods can have any access modifier (public, protected, private, or package-private) and can be either abstract or concrete.
Constructors: Interfaces cannot have constructors, whereas abstract classes can. This means that an abstract class can be used to provide a common constructor implementation for its subclasses.
Fields: Interface fields are implicitly public, static, and final, whereas abstract class fields can have any access modifier and can be either static or non-static.
Object class: An interface does not inherit from the Object class, whereas an abstract class does.

In general, interfaces are more appropriate for defining contracts that classes must adhere to, whereas abstract classes are more appropriate for providing a common implementation that can be shared by multiple subclasses.

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