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                JAVA INTERFACES

Overview:
 - Motivation 
 - Syntax and semantics
 - Interface constants and methods
 - Extending interfaces
 - Marker interfaces

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                  MOTIVATION

Q: Why is it important to think about the design and the 
   implementation separately?








- Ideas in an early form: abstract data types (We will 
  study them more closely later) and their algebraic 
  specifications

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                MOTIVATING EXAMPLE

 - A variety of drawing elements 
    > points, lines, triangles, circles, rectangles, 
      squares, ellipses, et

 - How do we draw all such elements uniformly?

Show code*

public class Point{
 int x;
 int y;
 public Point(){ x = 0; y = 0; }
 public int getX(){return x;}
 public int getY(){return y;}
 public void setX(int x){this.x = x;}
 public void setY(int y){this.y = y;}
 public void draw(){
   System.out.println(this.toString());
  }
 public String toString(){
    return "(" + x + "," + y + ")";
  }
 }

public class Line{
 Point p1;
 Point p2;
 public Line(Point p1, Point p2){this.p1 = p1; this.p2 = p2;}
 public int getP1(){return p1;}
 public int getP2(){return p2;}
 public void setP1(Point p1){this.p1 = p1;}
 public void setP2(Point p2){this.p2 = p2;}
 public void draw(){
    System.out.println("[" + p1.toString() + "=>" +  p2.toString() + "]");
   }
 }


Alternative:

   Abstract class FigureElement

     - provides an abstract draw method
     - point, line, etc implement the interface
     - all FigureElements provide a concrete implementation

   What about multiple inheritance?


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             MULTIPLE INHERITANCE 

Explain:




Why helpful?




What are some problems?



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      DO INTERFACES PROVIDE MULTIPLE INHERITANCE?

- Is it easier to talk about interface-based multiple
  inheritance compared to class-based multiple 
  inheritance?




Mention Mix-ins briefly (Will come back to it).
Mention Open-classes briefly (Will come back to it).
Mention Hyperspaces briefly (Will come back to it).
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