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second/semester1/logseq-stuff/pages/Interfaces.md

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+- #[[CT2106 - Object-Oriented Programming]]
+- **Previous Topic:** [[Abstraction & Polymorphism]]
+- **Next Topic:** [[Static Fields & Exceptions]]
+- **Relevant Slides:** ![Lecture-15__2022.pdf](../assets/Lecture-15_2022_1666857889307_0.pdf) ![Lecture-16__2022.pdf](../assets/Lecture-16_2022_1666857979984_0.pdf)
+-
+- # Multiple Inheritance
+	- What is **multiple inheritance**? #card
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+	  card-last-reviewed:: 2022-11-14T20:22:31.708Z
+	  card-last-score:: 5
+		- **Multiple inheritance** is where a class has multiple simultaneous superclasses.
+		- 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.
+- # Interface
+	- What is an **interface**? #card
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+	  card-last-reviewed:: 2022-11-14T20:25:49.659Z
+	  card-last-score:: 5
+		- Java uses a structure called an **interface** to achieve a form of *multiple inheritance*.
+			- An interface is like a class, but it is really more like ==an outline of what methods a class should have.==
+		- Like a class, an interface can be used as a **type**.
+		- By convention, interface names often end in -`able`.
+		- While a class can only extend one super class (direct inheritance), a class can implement multiple interfaces.
+	- ## Examples
+		- ```java
+		  public interface Eatable
+		  {
+		    public int getCalories();	// note: method definitions have no body
+		    public int extractEnergy;
+		  }
+		  ```
+		- ```java
+		  public class Canary extends Bird implements Food, Comparable() ....
+		  ```
+	- What does it mean if a class implements an interface? #card
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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).
+		  2. Any class that implements that interface *must* provide **concrete implementations** of its method.
+	- ## Interface VS Abstract
+		- ### Similarities
+			- Both can be used to provide "templates" for what subclasses can implement.
+			- An abstract method plays the same role as an interface method - both *must* be implemented in concrete form by a subclass.
+			- An abstract class and an Interface can be used as the **type** for a reference variable.
+		- ### DIfferences
+			- An abstract class is used for class inheritance purposes - providing an abstract structure that subclasses inherit. Therefore, the subclasses have a lot in common.
+			- However, an interface is often used to impose common functionality on classes that have nothing in common.
+			-