Differences between interfaces and classes

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 In Java, there are several differences between interfaces and classes. Here are some key differences:

  1. Purpose: A class is used to define a blueprint for creating objects that encapsulate data and behavior. An interface, on the other hand, defines a contract for behavior that other classes must adhere to.

  2. Implementation: A class can be instantiated, which means that you can create objects from it. An interface cannot be instantiated directly, but other classes can implement it.

  3. Fields: A class can have instance variables and class variables (static fields). An interface can only have constant variables (static final fields).

  4. Constructors: A class can have constructors, which are used to initialize the state of objects. An interface cannot have constructors, since it cannot be instantiated.

  5. Inheritance: A class can extend another class, inheriting all of its non-private fields and methods. An interface can extend multiple other interfaces, but it cannot extend a class.

  6. Method implementation: In a class, all methods must be implemented, unless they are marked as abstract. In an interface, all methods are abstract by default, and do not have an implementation. Classes that implement an interface must provide an implementation for all of the methods declared in the interface.

  7. Access modifiers: In a class, methods and fields can have various access modifiers (public, private, protected, or package-private). In an interface, all methods and fields are implicitly public, and all fields are implicitly final (since they are constants).

In general, interfaces are used to define a contract for behavior, while classes are used to define the implementation of that behavior. Interfaces are often used in Java to create abstractions and decouple different parts of a program.

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