Is this correct ? I've attempted to declare variables outside parameters

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Java

class egg extends food{
    double protein;
    double fats;
    double carbs;
    public egg(protein, fats, carbs){//declaring outside the parameters
        this.protein = protein;
        this.fats = fats;
        this.carbs = carbs;
    }
   }

What I have tried:

Java

class egg extends food{
    double protein;
    double fats;
    double carbs;
    public egg(protein, fats, carbs){//declaring outside the parameters
        this.protein = protein;
        this.fats = fats;
        this.carbs = carbs;
    }
   }

Posted 16-Jul-22 3:28am

SamuelKalubi

Updated 16-Jul-22 6:39am

Dave Kreskowiak

v2

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0x01AA 16-Jul-22 9:54am

You should show also your class food.

SamuelKalubi 16-Jul-22 9:59am

yes food is an abstract class

0x01AA 16-Jul-22 10:01am

Show the code of that class, or is it confidential?

2 solutions

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OriginalGriff · Answer 1 · 2022-07-16T04:02:00

No.
When you declare variables at class level:

class egg extends food{
   double protein;
   double fats;
   double carbs;

You are saying "I need these to exist as separate items for each instance of the class I create" and they are available to all code within the class.

When you create variables as parameters they are local top that metho: they are created when the method is called, and destroyed when the method ends. They are not the same as class level variables even if they have the same name.
In fact, if you had correctly declared your constructor method parameters:

public egg(double protein, double fats, double carbs){
   ...

then they would do something called variable shadowing, which means that they would "hide" the class level variables of the same name and you wouldn't be able to get at the class level versions at all (unless you prefixed them with this which always references the current instance of the class:

public egg(double protein, double fats, double carbs){
   this.protein = protein;
   ...

Using this tells the compiler "which version" of the variable you are talking about in each case.

Richard MacCutchan · Answer 2 · 2022-07-16T05:26:00

Solution 2

Rather than guessing you should make use of Lesson: Object-Oriented Programming Concepts (The Java™ Tutorials > Learning the Java Language)[^].

Posted 16-Jul-22 5:26am

Richard MacCutchan