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.

CodePudding user response：

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.

CodePudding user response：

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);
    };