Thread: BlueJ inheritance Issue. Please Help.

Hello,

I'm working on my coursework and the task is to create inheritance using "super"
Screenshot_2.png
This is the structure.

public class Gadget
    {
        public String model;
        public double price;
        public int weight;
        public String size;
 
    public Gadget(String themodel, double theprice, int theweight, String thesize)
    {
        price = theprice;
        model = themodel;
        weight = theweight;
        size = thesize;
    }
 
    //Return The price of a gadget.
    public double getPrice()
    {
        return this.price;
    }
 
    //Return The model of a gadget.
    public String getModel()
    {
        return this.model;
    }
 
    //Return The weight of a gadget.
    public int getWeight()
    {
        return this.weight;
    }
 
    //Return The size of a gadget.
    public String getSize()
    {
        return this.size;
    }
}

This is my Gadget class.
For my Phone class i have this task:
The Mobile class is a subclass of the Gadget class and has just one attribute, which corresponds to the (whole) number of minutes of calling credit remaining. The attribute is initialized in the constructor by being assigned the value of one of the constructor's five parameters and it has a corresponding accessor method. The other parameters of the constructor represent the model the price, the weight and the size of the mobile phone and these four values are passed to the constructor of the Gadget class.

public class Phone extends Gadget
{
    private int credits;
    private int balance;
 
    public void Gadget(String themodel, double theprice, int theweight, String thesize)
    {
        super();
        credits = theCredits;
    }   
}

This is my Phone class and the same error i keep getting. I've checked my code 1000 times and it look 100% correct. I just can not understand why the "super" function doesn't want to work for me. I reinstalled BlueJ but it's still the same. Please i need your help because i can't even begin the task with the most basic function.
It's telling me that the super call must be the first statement but it already is! Please help

the same error i keep getting.

Please copy the full text of the error messages and paste it here. Not as images.

Check that the code is defining a constructor vs a method. Constructors do not have a return type.
Also constructors have the same name as the class.

The error code is "call to super must be first statement in constructor". But i believe that it's already the first statement..
There is also another message:
constructor Gadget in class Gadget cannot be applied to given types;
required: java.lang.String,double,int,java.lang.String
found: no arguments
reason: actual and formal argument lists differ in length

This is a big hurdle for me and i can't do anything else until i get this fixed..

call to super must be first statement in constructor

See my previous post about constructors vs methods.

Some examples from the Gadget code:

public class Gadget
    {
        public String model;
        public double price;
        public int weight;
        public String size;
 
    public Gadget(String themodel, double theprice, int theweight, String thesize)  //<<<<< the Constructor
 
 ....
 
    //Return The price of a gadget.
    public double getPrice()                                               //<<< defines a method
    {
        return this.price;
    }

Also see the tutorial: https://docs.oracle.com/javase/tutor...structors.html

https://docs.oracle.com/javase/tutor...O/methods.html

From post#2:
Constructors do not have a return type. void is a return type
Also constructors have the same name as the class.

public void Gadget(String themodel, double theprice, int theweight, String thesize)  // defines a method named Gadget

The constructor for the Phone class needs to be named Phone not Gadget.

still doesn't compile

Please copy the full text of the error message and paste it here. It has important info about the error.

There are several problems in your code but you need to learn to figure them out. The first hint is it doesn't compile which means it must have a compilation error message. What does it say? Paste the whole think in a post. Then we can help you interpret it.

Regards,
Jim

The error messages should have the source line and line number for where the error happens.
These two line describe the problem:

required: java.lang.String,double,int,java.lang.String
found: no arguments

The constructor takes the 4 arguments listed in the message but the code calling the constructor did not have any arguments.
Change the calling code so that it provides the required arguments: java.lang.String,double,int,java.lang.String

Oh ok, so i've added the arguments to the super call and the error disappeared. Now i have another error for the 2nd part "credits = theCredits;" saying:
cannot find symbol - variable theCredits

public class Phone extends Gadget
{
   private int credits;
   private int balance;
 
   public Phone(String themodel, double theprice, int theweight, String thesize)
   {
       super(themodel, theprice, theweight, thesize);
       credits = theCredits;
   }
 
   //Return the current balance of credits.
   public String getCredits()
   {
       return theCredits;
   }
}

should i remove the "credits = theCredits;" statement outside the constructor?
According to the examples i've seen it looks correct as it is..

Ok. I am confused about something. You should have also gotten the error.

The constructor gadget() is undefined.

When you invoked super() in the subclass, Phone, the default gadget() constructor was not defined (unless you put it there later and didn't tell us about it). It is normally there by default UNLESS you add an explicit constructor. Then the default constructor goes away.

Regards,
Jim

You no longer need a default constructor in Gadget since you don't call it. But earlier you should have received an error message when you invoked super() in the Phone class.

Here is an example:

class Foo {
   int v;
 
   public Foo(int v) {
	  this.v = v;
   }
}
 
class Bar extends Foo {
   public Bar(int v) {
	  super(); <<-- error because the constructor Foo() no longer exists.
   }
}

Anyway, sorry for the distraction.

Regards,
Jim