Classes and Interface

Memory Map

This is section is about Interface vs Class and in-depth content on usage of each.

Following rules are described:

1. Item 15: Minimize the accessibility of classes and members
2. Item 16: In public classes, use accessor methods, not public fields
3. Item 17: Minimize mutability
4. Item 18: Favor composition over inheritance
5. Item 19: Design and document for inheritance or else prohibit it
6. Item 20: Prefer interfaces to abstract classes
7. Item 21: Design interfaces for posterity
8. Item 22: Use interfaces only to define types
9. Item 23: Prefer class hierarchies to tagged classes
10. Item 24: Flavor static member classes over non-static
11. Item 25: Limit source files to a single top-level class

Highlights of section –

Terms
Implementation inheritance- when a class extends another class and
Interface inheritance– when a class implements interface or an interface extends another interface.

Loopholes in using Inheritance:

• [WRONG Statement]The problems with overriding methods-
  1. Ambiguity in case of lack of Documentation – The case of counting elements of Hashset<>:
     1. there are 2 mehods adding elments to hashset like: add() and addAll()
     2. the case is- that we have to count number of elements in hash set .
     3. we add 3 elements using addall(),and then when we call to user defined function count it RETURNS 6.
     4. Blunder !!!! so internally addAll calls add() method and so it us inserted twcie . this issue occured beasue[Conclusion] there is no documentation for the fact that addAll() call add internally.
  2. [The case of having predicate before adding in a: ]
     • the problem in inheritance in which method is added not overridden. Suppose you add a method and then in later releases java library also releases method with same signature in super class then your class will be fragile class.

summary :

Use inheritance after aptly analysing if there exists IS-A relationship then class B can extends class A i.e class-B IS-A class-A.
Inherit a class only if it made to be inherited else have proper documentation to avoid blunder as we saw in case 1