6. Interfaces Lesson¶

Introduction to Interfaces¶

Introduction to Interfaces

Sample solutions not included, because "Show Solutions" was not toggled before printing.

Note

Activity objective: Show the benefits of interfaces at a high level. We want students to consider when it is appropriate to use an interface.

The Drawable Interface¶

The Drawable Interface

Sample solutions not included, because "Show Solutions" was not toggled before printing.

Note

Activity objective: Show the benefits of interfaces using an example we can refactor.

Step 1: Write out disparate classes along with the main method that calls a method to draw each (name the draw method differently). The draw methods will need to be in the driver class for the first step.

Step 2: Show how we can refactor the code and put the draw method in each class and then adjust the main method.

Step 3: Add an interface and show the resulting UML diagram. The classes/relationships have changed. However, the main method is so much cleaner and won't need to be modified later.

Note

Reference: Interface and Class Listings

Listing 34 in cs1302/draw/Drawable.java¶

package cs1302.draw;

public interface Drawable {

    void draw();

} // Drawable

Listing 35 in cs1302/draw/Tree.java¶

package cs1302.draw;

import java.awt.Color;

public class Tree implements Drawable {

    private int height;
    private Color trunkColor;

    public Tree(int height, Color trunkColor) {
        this.height = height;
        this.trunkColor = trunkColor;
    } // Tree

    public void grow(int amount) {
        this.height += amount;
        System.out.println("The tree is now " + height + " feet tall.");
    } // grow

    public int getHeight() {
        return this.height;
    } // getHeight

    public Color getTrunkColor() {
        return this.trunkColor;
    } // getTrunkColor

    @Override
    public void draw() {
        System.out.println("**** Gathering info to draw Tree ****");
        System.out.printf("Getting trunk color... %s\n", this.getTrunkColor());
        System.out.printf("Getting the height... %d\n", this.getHeight());
        System.out.println("Doing some math...");
        System.out.println("**** Rendering Tree ****");
        System.out.printf(
            "This %s tree is %d meters tall.\n",
            this.getTrunkColor().toString(),
            this.getHeight()
        );
    } // draw

} // Tree

Listing 36 in cs1302/draw/Person.java¶

package cs1302.draw;

import java.awt.Color;

public class Person implements Drawable {

    private Color eyeColor;
    private Color hairColor;

    public Person(Color eyeColor, Color hairColor) {
        this.eyeColor = eyeColor;
        this.hairColor = hairColor;
    } // Person

    public void describeAppearance() {
        System.out.println("This person has " +
                           eyeColor.toString() + " eyes and " +
                           hairColor.toString() + " hair.");
    } // describeAppearance

    public Color getEyeColor() {
        return this.eyeColor;
    } // getEyeColor

    public Color getHairColor() {
        return this.hairColor;
    } // getHairColor

    @Override
    public void draw() {
        System.out.println("**** Gathering info to draw the Person ****");
        System.out.printf("Getting eye color... %s\n", this.getEyeColor());
        System.out.printf("Getting hair color... %s\n", this.getHairColor());
        System.out.println("**** Rendering Person... ****");
        System.out.printf(
            "This is a person with eye color %s and hair color %s.\n",
            this.getEyeColor(),
            this.getHairColor()
        );
    } // draw

} // Person

Listing 37 in cs1302/draw/Airplane.java¶

package cs1302.draw;

import java.awt.Color;

public class Airplane implements Drawable {

    private Color paintColor;
    private int numberOfWheels;
    private double length;

    public Airplane(Color paintColor, int numberOfWheels, double length) {
        this.paintColor = paintColor;
        this.numberOfWheels = numberOfWheels;
        this.length = length;
    } // Airplane

    public void fly() {
        System.out.printf(
            "The %s airplane, with %d wheels and a length of ~ %.2f meters, is flying high!\n",
            this.paintColor,
            this.numberOfWheels,
            this.length
        );
    } // fly

    public Color getPaintColor() {
        return this.paintColor;
    } // getPaintColor

    public int getNumberOfWheels() {
        return this.numberOfWheels;
    } // getNumberOfWheels

    public double getLength() {
        return this.length;
    } // getLength

    @Override
    public void draw() {
        System.out.println();
        System.out.println("**** Gathering info to draw Airplane ****");
        System.out.printf("Getting paint color... %s\n", this.getPaintColor());
        System.out.printf("Getting the number of wheels... %d\n", this.getNumberOfWheels());
        System.out.printf("Getting the length... ~ %.2f\n", this.getLength());
        System.out.println("**** Rendering Airplane... ****");
        this.fly();
    } // draw

} // Airplane

Listing 38 in cs1302/draw/Flower.java¶

package cs1302.draw;

import java.awt.Color;

public class Flower implements Drawable {

    private Color petalColor;
    private int numberOfPetals;

    public Flower(Color petalColor, int numberOfPetals) {
        this.petalColor = petalColor;
        this.numberOfPetals = numberOfPetals;
    } // Flower

    public void bloom() {
        System.out.println("The flower with " +
                           numberOfPetals + " petals is blooming!");
    } // bloom

    public void changeColor(Color newColor) {
        this.petalColor = newColor;
        System.out.println("The flower's color has been changed to " + newColor);
    } // changeColor

    public Color getPetalColor() {
        return this.petalColor;
    } // getPetalColor

    public int getNumberOfPetals() {
        return this.numberOfPetals;
    } // getNumberOfPetals

    @Override
    public void draw() {
        System.out.println("**** Gathering info to draw Flower ****");
        System.out.printf("Getting petal color... %s\n", this.getPetalColor());
        System.out.printf("Getting the number of petals... %s\n", this.getNumberOfPetals());
        System.out.println("**** Rendering Flower... ****");
        System.out.printf(
            "This %s flower has %d petals!\n",
            this.getPetalColor(),
            this.getNumberOfPetals()
        );
    } // draw

} // Flower

Listing 39 in cs1302/draw/Utility.java¶

package cs1302.draw;

public class Utility {

    public static void drawIt(Drawable obj) {
        obj.draw();
    } // drawIt

    public static void drawAll(Drawable[] objs) {
        for (Drawable obj : objs) {
            obj.draw();
        } // for
    } // drawAll

} // Utility