繼承方法求圓和矩形面積

 

//Area.java

public abstract class Area{
 public abstract double area();
}

//RoundArea.java

public class RoundArea extends Area {
 private double radii;
 RoundArea(){}
 RoundArea(double r){
 radii=r;
 }
 public double area() {
 return Math.PI*radii*radii;
 }
}

//RectArea.java

public class RectArea extends Area {
 private double length;
 private double width;
 RectArea()
 {}
 RectArea(double l,double w){
  length=l;
  width=w;
 }
 public double area() {
  return length*width;
 }
}

//ImpleArea.java具體實現類

import javax.swing.JOptionPane;
import java.util.StringTokenizer;
public class ImpleArea {
 public static void main(String a[]) {
  String radiiString = JOptionPane.showInputDialog("Enter the radii of Round: ");
  double number_radii = Double.parseDouble(radiiString);
  RoundArea round = new RoundArea(number_radii);
  JOptionPane.showMessageDialog(null,"The area of round = "+round.area());
  String lengthAndWidth_String = JOptionPane.showInputDialog("Enter the length and the width of Rectangle: ");
  StringTokenizer length_Width_String=new StringTokenizer(lengthAndWidth_String);

//StringTokenizer類可以把字符串分成多個單詞。該類在標準的java.util軟件包中。
  double number_length = Double.parseDouble(length_Width_String.nextToken());
  double number_width=Double.parseDouble(length_Width_String.nextToken());
  RectArea rectangle = new RectArea(number_length, number_width);
  JOptionPane.showMessageDialog(null, "The area of rectangle =" + rectangle.area());

 }
}