Abstract type: Difference between revisions

Java has an ''interface'' and an ''abstract class''. Neither of which can be instantiated, and require some sort of implementation or abstraction.<br />

For an ''interface'', only the ''private'' and ''default'' access modifiers are allowed, which also implies they require code.<br />

A ''private'' method cannot be overridden by a sub-class, and a ''default'' method, optionally, can.<br />

A method with no access modifier is inherently ''public'', must not contain code, and requires implementation by its sub-class.<br />

Member fields are allowed, although are effectively ''final'' and ''static'', thus requiring a value.<br />

Here is an example of an ''interface''.

The ''abstract class'' is very generalized, and for the most part is just a ''class'' that allows for un-implemented methods.<br />

The ''default'' access modifier is not used here, as it applies only to an ''interface''.<br />

Additionally, if a method is marked ''abstract'', then the ''private'' access modifier is not allowed, as the concept does not apply.<br />

Here is an example of an ''abstract class''. If the class contains ''abstract'' methods then the class definition must also have the ''abstract'' keyword.

Here is an example of a class which ''extends'' an ''abstract class''.