如何重写基于周长进行比较的矩形类中的compareTo方法？

Question

I have a rectangle class here and I need to override the compareTo method so that it compares based on the rectangle's perimeters. I know the current compareTo method I have is wrong but I don't know how to fix it.

here is the code:

public class Rectangle implements Comparable<Rectangle> {
    private double length;
    private double width;
        private double perimeter;


    public Rectangle(double l, double w){
        this.length = l;
        this.width = w;
    } 

    public  double getLength() {
        return length;
    }

    public  double getWidth(){
        return width;
    }

        public void setLength(double l){
            length= l;
        }
        public void setWidth(double w){
            width = w;
        }

    public double getPerimeter(){
        perimeter = 2*(width + length);
                return perimeter;
    }


        @Override
        public int compareTo(Rectangle other){
                String t=Double.toString(perimeter);
                String o=Double.toString(other.perimeter);
        int comp = t.compareTo(o);

               return comp;
        }

        @Override
        public String toString(){
            return "Rectangle: "+ width +" by "+ length ;
        }




}

Answer 1

Try this

 public int compareTo(Rectangle otherRectangle) {
    return Double.compare(this.getPerimeter(), otherRectangle.getPerimeter());
}

Answer 2

Try this: You need to use getPerimeter because your calculation logic lies there:

@Override
    public int compareTo(Rectangle other){
          return Double.compare(getPerimeter(), other.getPerimeter());
    }

Answer 3

All the other answers are correct. This answer just adds an array of rectangles and sorts them based on their perimeters using java.util.Array.sort to demonstrate that the comparator is working. Also, the calculation of the perimeter is moved into the constructor, instead of the getPerimeter method.

import java.util.Arrays;

public class Rectangle implements Comparable<Rectangle> {
    private double length;
    private double width;
    private double perimeter;


    public Rectangle(double l, double w){
        this.length = l;
        this.width = w;
        perimeter = 2 *(width+length);
    } 

    public  double getLength() {
        return length;
    }

    public  double getWidth(){
        return width;
    }

    public void setLength(double l){
        length= l;
    }
    public void setWidth(double w){
        width = w;
    }

    public double getPerimeter(){
        perimeter = 2*(width + length);
        return perimeter;
    }


    @Override
    public int compareTo(Rectangle other){
        return Double.compare(perimeter, other.perimeter);
    }

    @Override
    public String toString(){
        return "Rectangle: "+ width +" by "+ length ;
    }

    public static void main(String args[]) {
        Rectangle [] arrayOfRectangles = new Rectangle [3];
        arrayOfRectangles[0] = new Rectangle(1.0,1.0);
        arrayOfRectangles[1] = new Rectangle(6.0,5.0);
        arrayOfRectangles[2] = new Rectangle(2.0,3.0);
        Arrays.sort(arrayOfRectangles);
        for (int i = 0; i < 3; i++) {
            System.out.println(arrayOfRectangles[i]);
        }
    }




}

Answer 4

Few things -

1. You can evaluate the parameter of a Rectangle within the constructor instead of the getter as

    public Rectangle(double l, double w) { this.length = l; this.width = w; this.perimeter = 2 * (this.width + this.length); } 

   and then your perimeter s getter and setter be like -

    public double getPerimeter() { return perimeter; } public void setPerimeter(double perimeter) { this.perimeter = perimeter; } 

2. You can compare using the Double class compare method as

    @Override public int compareTo(CompareToRectangle other) { return Double.compare(this.perimeter, other.perimeter); } 

3. You can test the same using a test method as -

    public static void testRectangle() { Rectangle first = new Rectangle(2.00, 3.00); Rectangle second = new Rectangle(4.00, 3.00); if (first.compareTo(second) == 0) { System.out.println("Similar rectangles."); } else if(first.compareTo(second) == 1) { System.out.println("First rectangle bigger than second."); } else { System.out.println("Second rectangle is bigger than first."); } }