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Build a Constructor

6 replies on 1 page. Most recent reply: Apr 15, 2002 6:11 AM by Thomas SMETS

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Thang Nguyen

Posts: 18
Nickname: thang
Registered: Apr, 2002

Build a Constructor

Posted: Apr 14, 2002 7:33 PM

I have an empty constructor for a class, called Point.
It is like below:

public class Point {
//ordered pair (x, y)
private int x;
private int y;
public Point(){
x=0;
y=0;
}
...
} ///:~

My question is: should I set the values of co-ordinates x and y to zero or ask the user (via the keyboard or so) to enter the values for x, y?
I am very new to Java. I would appreciate your answer. - Thang

Singh M.

Posts: 154
Nickname: ms
Registered: Mar, 2002

Re: Build a Constructor

Posted: Apr 14, 2002 8:05 PM

java already has a class called Point.

java.awt.Point. Make use of it.

Matt Gerrans

Posts: 1153
Nickname: matt
Registered: Feb, 2002

Re: Build a Constructor

Posted: Apr 14, 2002 10:12 PM

Singh, I think you missed the point.

Thang, you asked whether to set x and y in your program, or ask for input. Of course, it would generally be better to get that as input, rather than hardcoding it. You could either prompt for input (which would be different for a console app, vs. a GUI app), or you could allow it to be specified on the command line (get it from the args array). Either way, you will have to subsequently convert it from String format to int (or float, or double, etc.) using Integer.parseInt() (or Float.parseFloat(), etc.).

Singh M.

Posts: 154
Nickname: ms
Registered: Mar, 2002

Point(ed)

Posted: Apr 14, 2002 10:16 PM

Maybe. But, the fact that the person is a java newbie and probably would not have known about the existence of class Point I just "pointed" him to that class.

Thomas SMETS

Posts: 307
Nickname: tsmets
Registered: Apr, 2002

Re: Point(ed)

Posted: Apr 15, 2002 12:24 AM

One more remark (but nothing personnal, he guys !)

If one has the following code :


/** 
  */
public class Point
{
/** 
  */
  int x, y;
  Point ()
  {
  }
/** 
  */
  Point (int anX, int aY)
  {
    x = anX;
    y = aY;
  }
}

With the default constructor the x & y are de facto initialized to the default value for the int's.

Hence there is no need for a default initialization in the code !
At least an initialization to zero.

Thomas,

Thang Nguyen

Posts: 18
Nickname: thang
Registered: Apr, 2002

Re: Build a Constructor

Posted: Apr 15, 2002 5:54 AM

Signh, I did not know the existence of Point actually. I will find it out.

Matt, very informative answer.

Thomas, I have tried bulding constructors with a list of arguments. However, the problems is that in my class no one knows what we should deal with the empty constructors and more, with the list of arguments in other constructors, what should we do if the values of these arguments are not valid for the use within the constructor or class? In the case that invalid values passed in as arguments are detected, should I assign the programmer default values, such as for int, value is 0, and double is 0.0, and float is 0.0f, and string or char, and so on, is "Not defined"

Anyways, I have to say that it is very interesting to be here in the Forums which I just found last night. I spend hours here just to read people's, like you guys answers to different questions. Thanks a lot! - Thang

Thomas SMETS

Posts: 307
Nickname: tsmets
Registered: Apr, 2002

Re: Build a Constructor

Posted: Apr 15, 2002 6:11 AM

>
> However, the problems is that in my class
> no one knows what we should deal with the empty
> constructors and more, with the list of
> arguments in other constructors, what should
> we do if the values of these arguments are not
> valid for the use within the constructor or class?
>

Well if that's is the case, just make it private, so none can use it !

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