complete interface examples with applet

Author: ymzong

src/section13/Colored.java

@@ -0,0 +1,8 @@
+package section13;
+
+import java.awt.*;
+
+/* Trivial interface that describes a Color getter */
+public interface Colored {
+    Color getColor();       // method is implicitly public
+}

src/section13/ColoredDrawable.java

@@ -0,0 +1,6 @@
+package section13;
+
+/* Trivial subinterface that extends both Colored and Drawable */
+public interface ColoredDrawable extends Colored, Drawable {
+    // Nothing
+}

src/section13/ColoredDrawablePoint.java

@@ -0,0 +1,19 @@
+package section13;
+
+import java.awt.*;
+
+/* Enhance a ColoredPoint as drawable; implements ColoredDrawable since it also includes draw method */
+public class ColoredDrawablePoint extends ColoredPoint implements ColoredDrawable {
+
+    Color c;
+
+    public ColoredDrawablePoint(int x, int y, Color c) {
+        super(x, y, c);
+    }
+
+    public void draw(Graphics g) {
+        System.out.println("Drawing ColoredDrawablePoint...");
+        g.fillRect(x, y, 100, 100);
+    }
+
+}

src/section13/ColoredPoint.java

@@ -0,0 +1,25 @@
+package section13;
+
+import section9.BasicPoint;
+
+import java.awt.*;
+
+/* Enhance a BasicPoint object with Color; implements Colored interface by defining getColor method */
+public class ColoredPoint extends BasicPoint implements Colored {
+
+    Color c;
+
+    /* Constructor for ColorPoint has to exist because otherwise it would call the default constructor, super().
+     * However, super(), or BasicPoint() does not exist.
+     * See: https://stackoverflow.com/q/7187799
+     */
+    public ColoredPoint(int x, int y, Color c) {
+        super(x, y);
+        this.c = c;
+    }
+
+    public Color getColor() {       // must be public since it's part of Colored interface
+        return c;
+    }
+
+}

src/section13/ColoredRectangle.java

@@ -0,0 +1,28 @@
+package section13;
+
+import java.awt.*;
+
+/* Implements a Rectangle class based on ColoredDrawable interface */
+public class ColoredRectangle implements ColoredDrawable {
+
+    Color c;
+    int x1, x2, y1, y2;
+
+    public ColoredRectangle(int x1, int x2, int y1, int y2, Color c) {
+        this.x1 = x1;
+        this.x2 = x2;
+        this.y1 = y1;
+        this.y2 = y2;
+        this.c = c;
+    }
+
+    public Color getColor() {
+        return c;
+    }
+
+    public void draw(Graphics g) {
+        System.out.println("Drawing colored rectangle...");
+        g.fillRect(x1, y1, x2-x1, y2-y1);
+    }
+
+}

src/section13/Drawable.java

@@ -0,0 +1,8 @@
+package section13;
+
+import java.awt.*;
+
+/* Trivial interface that describes a draw method */
+public interface Drawable {
+    void draw(Graphics g);      // method is implicitly public
+}

src/section13/ShapeDrawingApp.java

@@ -0,0 +1,35 @@
+package section13;
+
+import javax.swing.*;
+import java.applet.Applet;
+import java.awt.*;
+
+/* This class uses the Colored* classes defined in the package */
+public class ShapeDrawingApp extends Applet {
+
+    /* Given an array of Colored, print out their colors */
+    static void printColors(Colored[] cs) {
+        for (Colored elem : cs) {
+            System.out.println(elem.getColor().toString());
+        }
+    }
+
+    /* Draws the ColoredDrawable by using its interface methods */
+    static void draw(Graphics g, ColoredDrawable[] cds) {
+        for (ColoredDrawable cd : cds) {
+            g.setColor(cd.getColor());      // get the color of Drawable with getColor()
+            cd.draw(g);                     // draw the shape with draw(Graphics)
+        }
+    }
+
+    /* This method will be invoked by the Applet to draw shapes */
+    @Override
+    public void paint(Graphics g) {
+        ColoredDrawablePoint p1 = new ColoredDrawablePoint(12, 12, new Color(12, 12, 12));
+        ColoredRectangle r1 = new ColoredRectangle(105, 305, 205, 355, new Color(33, 75, 152));
+        ColoredDrawable[] shapes = new ColoredDrawable[] { p1, r1 };
+
+        printColors(shapes);
+        draw(g, shapes);
+    }
+}

src/section9/BasicPoint.java

@@ -7,7 +7,7 @@
  */
 public class BasicPoint {
     // Two non-static fields
-    int x, y;
+    public int x, y;
 
     // One constructor
     public BasicPoint(int x, int y) {