Sunday, December 14, 2008

Differences between interface and abstract class

The interfaces and abstract classes, both can't be instantiated. While an abstract class contains both implemented and non-implemented methods, an interface contains only abstract methods.

  • An interface is pure contract
  • Interface must be public
  • It may be left unused after declaration
  • When used, Implementing class must override all methods provided by that interface.
  • It contains only unimplemented methods and no function definitions
  • Variable must be abstract and final
  • Methods take abstract as default.
  • A single class can implement multiple interfaces.
  • Interface properties are included with "implements" key word

  • Abstract class must contain at least one abstract method
  • It can contain function body
  • It contains both implented and unimplemented method.
  • It allows both abstract and non abstract methods.
  •  It must be used if declared, otherwise compiler gives an error.
  • It may be public or protected.
  • Only one class can extend abstract class.
  • Abstract properties are included with extends keyword.

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