Interfaces and Inner Classes

• Java does not support multiple inheritance
• A subclass can only have one direct parent
• Modes of transportation can be refueled
• Some modes of transportation can fly
• Some modes of transportation must drive on specified roads

Interfaces, Motivation

• Multiple inheritance subsitute, pull from one class
• Classes that implement that interface

Nested Classes

• Can specify a full class definition inside another class
• The inner class can access all of its own members, as well as all of the members of the class it is in
• Often used for helper classes
  • Classes whose only purpose is really to help with the outer class
  • Keep classes directly related to the outer class rgih with the outer class, instead of being in different files

Generics Motivation

• Generics are a lot like templates in C++
• Goal of generics
  • Allows a class to be written once and suppor the use of many data types

Basic Syntax for Generic Class

public class MyGenericClass <DataType>

public DataType myGenericDataMember;
// or
public DataType myMethod(double x, DataType y);

Using extends to Restrict Data Types

• Uses compareTo method -compareTo is in the Comparable interface, which thte Integer class implements
• When making the class generic, we're saying we support other data types too
• Need to be able to say this class is generic, but will only work on types that implement the Comparable interface
• This is done using keyword extends
• There is no differentiation between whether class must extend another class or implement an interface - extends is used for both