Interfaces

• Interfaces

  • What?

  • Why use?

  • Override method

  • Inheritence

  • Default Methods (JAVA8 +)

  • other

  • Links

What?

• is an abstract type that is used to specify a behavior that classes must implement.

  • Is just a contract. The implementing class ensures, that it will have these methods that can be used on it. It is basically a contract or a promise the class has to make.

  • A class can implement multiple interfaces

• A Java interface is a bit like a class, except a Java interface can only contain method signatures and fields. An Java interface cannot contain an implementation of the methods, only the signature (name, parameters and exceptions) of the method.

• Interfaces cannot be instantiated (does not container constructor), but rather are implemented. A class that implements an interface must implement all of the non-default methods described in the interface, or be an abstract class.

• Object references in Java may be specified to be of an interface type; in each case, they must either be null, or be bound to an object that implements the interface.

• Interfaces can extend multiple interfaces

• https://www.quora.com/If-asked-on-a-coding-interview-What-is-the-primary-difference-between-an-interface-and-abstract-class-what-is-the-correct-answer

Why use?

• Interfaces are the best way to maintain well decoupled constructs.

• You can use interfaces in Java as a way to achieve polymorphism.

Override method

• annotation

  • Use of @Override above method declaration, to say it is using the method from the interface

• Why?

  • https://stackoverflow.com/questions/94361/when-do-you-use-javas-override-annotation-and-why
  • https://javarevisited.blogspot.com/2012/11/why-use-override-annotation-in-java.html

Inheritence

• inherit from interfaces

  • classes

  • interfaces

• multiple inheritence

Default Methods (JAVA8 +)

• Issues

  • Multiple inheritence

other

• methods

• Reference types

  • polymorphism

  • cannot use concrete implementation class which has its own method with this ref type

Links