exercise9_8.java

java程序设计导论（daniel liang著） 所有偶数课后习题答案

// Exercise9_8.java:
public class Exercise9_8 {
  public static void main(String[] args) {
    new Exercise9_8();
  }

  public Exercise9_8() {
    GeometricObject[] a = {new Circle(5), new Cylinder(4, 5),
      new Rectangle(2, 3)};

    System.out.println("The total area is " + sumArea(a));
  }

  public static double sumArea(GeometricObject[] a) {
    double sum = 0;

    for (int i = 0; i < a.length; i++)
      sum += a[i].findArea();

    return sum;
  }

  // Rectangle.java: The Rectangle class that extends GeometricObject
public class Rectangle extends GeometricObject {
  private double width;
  private double height;

  /**Default constructor*/
  public Rectangle() {
    this(1.0, 1.0);
  }

  /**Construct a rectangle with width and height*/
  public Rectangle(double width, double height) {
    this(width, height, "white", false);
  }

  /**Construct a rectangle with specified width, height,
     filled, and color*/
  public Rectangle(double width, double height,
    String color, boolean filled) {
    super(color, filled);
    this.width = width;
    this.height = height;
  }

  /**Return width*/
  public double getWidth() {
    return width;
  }

  /**Set a new width*/
  public void setWidth(double width) {
    this.width = width;
  }

  /**Return height*/
  public double getHeight() {
    return height;
  }

  /**Set a new height*/
  public void setHeight(double height) {
    this.height = height;
  }

  /**Implement the findArea method in GeometricObject*/
  public double findArea() {
    return width*height;
  }

  /**Implement the findPerimeter method in GeometricObject*/
  public double findPerimeter() {
    return 2*(width + height);
  }

  /**Override the equals method defined in the Object class*/
  public boolean equals(Rectangle rectangle) {
    return (width == rectangle.getWidth()) &&
      (height == rectangle.getHeight());
  }

  /**Override the toString method defined in the Object class*/
  public String toString() {
    return "[Rectangle] width = " + width +
      " and height = " + height;
  }
}
}