57 lines
2.9 KiB
Markdown
57 lines
2.9 KiB
Markdown
- #[[CT2106 - Object-Oriented Programming]]
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- **Previous Topic:** [[Abstraction & Polymorphism]]
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- **Next Topic:** [[Static Fields & Exceptions]]
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- **Relevant Slides:**  
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- # Multiple Inheritance
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- What is **multiple inheritance**? #card
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card-next-schedule:: 2022-11-17T21:22:31.707Z
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card-last-reviewed:: 2022-11-14T20:22:31.708Z
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card-last-score:: 5
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- **Multiple inheritance** is where a class has multiple simultaneous superclasses.
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- However, Java does not support multiple inheritance as it has led to major problems in OOP due to conflicting field & method implementations inherited from superclasses.
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- # Interface
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- What is an **interface**? #card
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card-next-schedule:: 2022-11-17T21:25:49.658Z
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card-last-reviewed:: 2022-11-14T20:25:49.659Z
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- Java uses a structure called an **interface** to achieve a form of *multiple inheritance*.
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- An interface is like a class, but it is really more like ==an outline of what methods a class should have.==
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- Like a class, an interface can be used as a **type**.
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- By convention, interface names often end in -`able`.
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- While a class can only extend one super class (direct inheritance), a class can implement multiple interfaces.
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- ## Examples
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- ```java
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public interface Eatable
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{
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public int getCalories(); // note: method definitions have no body
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public int extractEnergy;
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}
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```
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- ```java
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public class Canary extends Bird implements Food, Comparable() ....
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```
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- What does it mean if a class implements an interface? #card
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card-next-schedule:: 2022-11-15T15:21:59.543Z
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card-last-reviewed:: 2022-11-14T16:21:59.544Z
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- 1. Any class that implements said interface can be treated as that interface's type (polymorphism).
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2. Any class that implements that interface *must* provide **concrete implementations** of its method.
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- ## Interface VS Abstract
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- ### Similarities
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- Both can be used to provide "templates" for what subclasses can implement.
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- An abstract method plays the same role as an interface method - both *must* be implemented in concrete form by a subclass.
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- An abstract class and an Interface can be used as the **type** for a reference variable.
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- ### DIfferences
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- An abstract class is used for class inheritance purposes - providing an abstract structure that subclasses inherit. Therefore, the subclasses have a lot in common.
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- However, an interface is often used to impose common functionality on classes that have nothing in common.
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