why can't i use a field variable in a construction by referring this keyword

Question

I created my main use constructor with three parameter passed. the parameter above a default parameter. the goal is to set the first field which is name to be default assume user doesnt input a name. the problem come as for creditLimit and email i get the error below. why is this and what is it i do not understand? and what are the fixes.

- Cannot refer to an instance field creditLimit while explicitly invoking a 
 constructor
- Cannot refer to an instance field email while explicitly invoking a 

public class VipCustomer {
    private String name;
    private int creditLimit;
    private String email;

    public VipCustomer() 
    {
        this("Default",creditLimit,email);
    }

    public VipCustomer(String name, int creditLimit, String email) {
        // TODO Auto-generated constructor stub
        this.name = name;
        this.creditLimit = creditLimit;
        this.email = email;
    }
    public String getName() 
    {
        return this.name;
    }
    public int getCreditLimit() 
    {
        return creditLimit;
    }

score 3 · Answer 1 · answered Sep 22 '19 at 23:41

The Problem

There seems to be an issue with your first constructor which calls with second constructor with the following parameters at runtime:

this ("Default", 0, null);

This is because the values of creditLimit and email are not set.

creditLimit defaults to 0 as that is the default for ints.
email defaults to null because it is an empty object reference.

The Solution

To fix this issue, I recommend having some final fields at the top of your class that define default behavior.

public class VipCostumer {

    // Change these values to what you would like.
    public static final String DEFAULT_NAME = "Default";
    public static final int DEFAULT_CREDIT = 100;
    public static final String DEFAULT_EMAIL = "example@abc.com";

    public VipCostumer() {
        this(DEFAULT_NAME, DEFAULT_CREDIT, DEFAULT_EMAIL);
    }

    // rest of your code

}

Trade Off

While this may resolve your issue, I would recommend you consider whether or not you want to have defaults for something as specific as a costumer. Depending on your usage, you may want all costumer data to be differentiable, and creating a lot of a default costumers will take that ability away.

score 1 · Answer 2 · edited Sep 22 '19 at 23:53

1

There is a problem with your first constructor, because it will call the second constructor (the one with the parameters), but you just try to set undefined variables to themselves.

edited Sep 22 '19 at 23:53

Max Vollmer

8,412
9
28
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answered Sep 22 '19 at 23:24

GitPhilter

171
9

score 0 · Answer 3 · answered Sep 23 '19 at 00:26

If your goal is to set the first field which is name to be default assume user doesnt input a name, use this constructor

    public VipCustomer() 
    {
       this.name = "Default";
    }

if creditLimit and email is a required value while name is not

    public VipCustomer(int creditLimit, String email) {
        this.name = "Default";
        this.creditLimit = creditLimit;
        this.email = email;
    }

why can't i use a field variable in a construction by referring this keyword

3 Answers3

The Problem

The Solution