super classes and sub classes

[kenji mapes]

Assume I have a default and a param constructor in both a subclass and a super class. The members are private.

So after validation logic in the sub class param. constructor, I want to access an instance variable of the super class's default constructor to set the subclass's matching variable to the default in the super class.

Is there anyway I can do this. Of course, I have inherited setters and getters.

Thanks.

[Eric McIntyre]

Could you post a simple code example? I'm not really clear on what you'd like to accomplish.

[Campbell Ritchie]

You have set your fields as private, eg

private int a;
private double b;
private String c;  ?

Then you have public get and set methods for a b c?
Then you have more variables in your subclass?

private otherType d;

Then you have default constructors?

public class Superclass{
    public SuperClass()
    {
        a = 1;
        b = 2.3;
        c = "Campbell Ritchie";
    }
}
. . . 
public class Subclass extends Superclass{
    public Subclass()
    {
        super();
    }
}  

. . . and parameter constructors?

public Superclass(int a, double b, String c)
    {
        this.setA(a);
        this.setB(b);
        this.setC(c);
    }
 . . . 
 
public Subclass(int a, double b, String c, otherType d)
    {
        super(a, b, c);
        this.setD(d);
    }
 . . .   

[You might be able to dispense with the no-parameter constructor in the subclass, as long as you don't plan to extend it to SubSubclass .]
Then you want to set a and c and leave b unchanged. How about this?

  . . . 
public Subclass(int a, String c, otherType d)
{
    super();
    this.setA(a);
    this.setC(c);
    this.setD(d);
} 

I have no idea whether it works, but try it out and tell us what happens.
CR

[kenji mapes]

Yeah, exactly. I'll try it out.

[kenji mapes]

Here's part of the super class

public class Car implements Cloneable
{
private int year;
private int numDoors;
private double carPrice;
private String model;
private String color;

public Car()
{
year = 2002;
numDoors = 4;
color = "Blue";
carPrice = 12500;
model = "Nissan Altima";

}

public Car(int yr, int numD, String col, double carP, String mod)
{
// if_else to control year - sets to default year if invalid

if((yr >= 1970) && (yr <= 2005))
year = yr;

else
year = 2002;

// if_else to control # car doors - sets to default car doors if invalid

if((numD > 0) && (numD <= 5))
numDoors = numD;

else
numDoors = 4;

//no conditions for color

color = col;

// if_else to control car price - sets to default car prices if invalid

if((carP <= 50000) && (carP > 0))
carPrice = carP;

else
carPrice = 12500;

//no conditions for model

model = mod;

}

Now here's the sub

public class FamilyCar extends Car
{

private int mileage;

public FamilyCar()
{
super();
mileage = 15000;

}

public FamilyCar(int yr, int numD, String col, double carP, String mod, int mil)
{
// if_else to control year - sets to default year if invalid

if((yr >= 1970) && (yr <= 2005))
year = yr;

else
year = 2005;

// if_else to control # car doors - sets to default car doors if invalid

if(numD == 4)
numDoors = numD;

else
numDoors = 4;

//color must be Blue, black, Maroon, or Grey

if(col.equalsIgnoreCase("blue"))
color = col;
else if(col.equalsIgnoreCase("black"))
color = col;
else if(col.equalsIgnoreCase("maroon"))
color = col;
else if(col.equalsIgnoreCase("grey"))
color = col;
else
color = "blue";

// if_else to control car price - sets to default car prices if invalid

if((carP <= 20000) && (carP > 0))
carPrice = carP;

else
carPrice = 12500;

//no conditions for model

model = mod;

//validation logic for mileage

if((mil >= 1) && (mil <=200000 ))
mileage = mil;
else
mileage = 15000;

}

It has an extra data field. If you look in the param constructor in the sub class, instead of explicitly assigning blue as a defualt in the if else validation logic, I'd like to be able to conditionally assign it to the super class's default, which of course is blue. This is why I'd like to access the super's data field?

Almost exactly as you portrayed it Cambell How you could infer what I wanted to do from my shallow explanantion is bizzaro.
[ November 02, 2005: Message edited by: kenji mapes ]

[Eric McIntyre]

So you just want to make "blue" either a constant, or pull it into a method. Either

protected static final String DEFAULT_COLOR = "Blue";
public Car()
{
  year = 2002;
  numDoors = 4;
  color = DEFAULT_COLOR;
  carPrice = 12500;
  model = "Nissan Altima";
}

or

public Car()
{
  year = 2002;
  numDoors = 4;
  color = getDefaultColor();
  carPrice = 12500;
  model = "Nissan Altima";
}
 
protected String getDefaultColor() {
  return "Blue";
}

The advantage of using the constant is that it's very simple to implement; the advantage of the protected method is that it's more extensible (in case a subclass wants a different default color).

As a side note on design, you've got a lot of duplicate code in there. The subclass constructor might be better off delegating to the super, then validating the color after the fact. Also, if your setters need the same data validation, move that logic out of the constructor and delegate to the setters.

Eric

[Campbell Ritchie]

We try our hardest.