I need help creating a Rectangle class with private instance variables, but public methods and constructors

Question

I'm new to using java and I need to make a class called Rectangle, but the code I'm using doesn't seem to work, and the notes for class aren't helpful. I feel like it has something to do with my methods because I don't understand those too well.

The class needs to follow these requirements: Create a class called rectangle with the following instance variables and public constructors:

• width, double

• height, double

• a constructor with one parameter (double) called sideLength, which sets both the width and height to sideLength.

• a constructor with two parameters width and height (double), which sets both the width and height to the corresponding values that are passed on.

• a public method computeArea with no parameters that returns the area of Rectangle as a double

• a public method computePerimeter with no parameters that returns the perimeter of Rectangle as a double

• a public method getHeight with no parameters that returns the height of Rectangle as a double

• a public method getWidth with no parameters that returns the width of Rectangle as a double

I don't need to make a main method because that was already provided.

This is the code that I'm using, but I keep getting an error that says height cannot be found from the computeArea method and down.

 class Rectangle{
     
     private static double width;
     private static double heigth;
     
     public Rectangle(double sideLength) {
         
         Rectangle width = new Rectangle(sideLength);
         Rectangle height = new Rectangle(sideLength);
     }
         
     public Rectangle(double width, double height){
         width = width;
         height = height;
     }    

     public double computeArea() {
         return height * width;
     }
         
     public double computePerimeter() {
         return 2 * (height + width);
     }
         
     public double getHeight() {
         return height;
     }
     
     public double getWidth() {
         return width;
     }
     
 }

Answer 1

Don't make the private variables static or they will be shared by all instances of Rectangle.

class Rectangle{
     
     private double width;
     private double height;
     
     public Rectangle(double sideLength) {
         
         this.width = sideLength;
         this.height = sideLength;
     }
         
     public Rectangle(double width, double height){
         this.width = width;
         this.height = height;
     }    

     public double computeArea() {
         return height * width;
     }
         
     public double computePerimeter() {
         return 2 * (height + width);
     }
         
     public double getHeight() {
         return height;
     }
     
     public double getWidth() {
         return width;
     }
 }

To use it in other code:

public class Test {
  public static void main(String[] args) {
    Rectangle square = new Rectangle(1.0);
    double area = square.computeArea();
    System.out.println(area);
    Rectangle rectangle = new Rectangle(1.0, 2.0);
    area = rectangle.computeArea();
    System.out.println(area);
  }
}

Answer 2

"... I keep getting an error that says height cannot be found from the computeArea method and down. ..."

This is because height is declared as static, thus cannot be accessed from the non-static, instance method.

class Rectangle {
    double width, height;

    Rectangle(double sideLength) {
        width = height = sideLength;
    }

    Rectangle(double width, double height) {
        this.width = width;
        this.height = height;
    }

    public double computeArea() {
        return width * height;
    }

    public double computePerimeter() {
        return 2 * (width + height);
    }

    public double getHeight() {
        return height;
    }

    public double getWidth() {
        return width;
    }
}

Alternately, use a record.

record Rectangle(double width, double height) {
    Rectangle(double sideLength) {
        this(sideLength, sideLength);
    }
    
    public double computeArea() {
        return width * height;
    }
    
    public double computePerimeter() {
        return 2 * (width + height);
    }
}