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The other questions I have seen are about intentionally referencing a superclass constructor method and failing. I am not referencing a constructor yet; just trying to extend a class.

I am creating the class Square.java, which extends Rectangle.java.

Square.java is the subclass of Rectangle.java.

Interface.java

-Abstract.java - abstract class Abstract implements Interface.java

--Rectangle.java - public class Rectangle extends Abstract

---Square.java - public class Square extends Rectangle.

When compiling Square.java, I received the error message.

Square.java:3: error: constructor Rectangle in class Rectangle cannot be applied to given types;
public class Square extends Rectangle {
       ^
  required: String,String,String,double,double
  found:    no arguments
  reason: actual and formal argument lists differ in length
1 error

The content of Square.java is

public class Square extends Rectangle {
       //no code is in the body

        }

The constructor method of rectangle is:

public Rectangle (String t,String n, String c, double w, double h ){
width = w;
height = h;
color = c;
name = n;
type = t;
    };

I want to create Square.java. Within this file, I would like to modify the Rectangle constructor method. But for right now, I just want the file to compile.

I have tried

  • Copying the Rectangle constructor method into Square.java. That resulted in the same error message.
  • Copying in the Rectangle constructor method and changing the name of the constructor method to Square. This resulted in the same error message.
  • Commenting out the Rectangle constructor method within Rectangle.java. Square.java compiled without a problem. But... I need the Rectangle constructor in Rectangle.java.
  • Creating a new Square constructor method and ran into more errors. Eventually, I want the Square constructor method to be a modified Rectangle constructor method.

From my understanding, constructor methods are not passed on to subclasses. I have not written code to intentionally reference the Rectangle constructor.

I am getting the feeling that the compiler is interpreting "... extends Rectangle { " as an attempt to reference the constructor instead of the class. I have run out of ideas on how to resolve this.

Thank you for any help.

Marcus
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2 Answers2

2
  1. All classes must contain at least one constructor. They cannot be compiled without having one.
  2. All constructors must begin with a super() call of some sort (invoking a constructor in the parent class), unless they start with a this() call (redirect to another constructor).
  3. ... However, if you fail to add a super() call, the compiler will simply assume you meant to and acts as if you wrote super(); at the top of it.
  4. ... However, if you fail to add a constructor, the compiler will simply assume you meant to write one, and acts as if you wrote: public MyClassName() { super(); }.

With these facts in mind, super() is not going to work in your case, because Rectangle does not have a no-args constructor.

All you need:

public class Square extends Rectangle {
  public Square(String t, String n, String c, double w) {
    super(t, n, c, w, w);
  }
}

This means Square has 1 constructor, taking 't', 'n', and 'c', whatever those are, as well as a single double indicating the length of any edge. (NB: This is bad code style, parameters should have clear names, especially if the type of the parameter isn't particularly enlightening. 'String c' means nothing. Color c - you can get away with that)

It then calls the Rectangle constructor, passing that 'edge length' value for both the width and height dimensions.

rzwitserloot
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The problem was solved with the help of this question. Similar content

I create another constructor with super(), this resolved the error.

public Square (String t,String n, String c, double w, double h ){
            super(t,n,c,w,h);
    };
Marcus
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  • This doesn't make sense - it would let you make a square instance that isn't a square, i.e. - an 'object with invalid state': What if I call new Square(t, n, c, 10, 20);? – rzwitserloot Dec 10 '22 at 17:05
  • You're correct. The constructor isn't finished yet I still need to modify it to ensure the width and height are the same – Marcus Dec 10 '22 at 17:17