Thread: Why doesnt my constructor work?

Hi

I'm new to Java & am working through the Dietels' "Java How to Program" and am stuck on exercise 6.1 (I'm not doing a formal course)
I managed to get the bulls eye required but I can't seem to get my constructor to 'work' - one of the circles should be red the colours when I create a DrawBullseye object but it defaults to black.

Any suggestions gratefully appreciated


[highlight = JAVA]
import java.util.Random;
import javax.swing.JFrame;

public class DrawSmileyTest
{

public static void main(String[] args)
{
DrawBullseye target = new DrawBullseye(200,0,0);
JFrame frame = new JFrame();

frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE);
frame.add(target);
frame.setSize( 250,250);
frame.setVisible(true);
}

}
[/highlight]

[highlight = Java]
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JPanel;
import java.util.Random;

public class DrawBullseye extends JPanel
{
int counter = 0;

int red1;
int green1;
int blue1;

int red2 = 99;
int green2 = 182;
int blue2 = 222;


public DrawBullseye(int r1, int g1, int b1)
{
red1 = r1;
green1 = g1;
blue1 = b1;
}
Color firstColour = new Color(red1, green1, blue1);
Color secondColour = new Color (red2, green2, blue2);

public void paintComponent (Graphics g)

{
super.paintComponent(g);
for (int l = 1; l<=10; l++)
{
int step = 10;
g.setColor(firstColour);
g.fillOval( 10 + (counter*step), 10 + (counter*step), 200 - (counter*2*step), 200 - (counter*2*step) );

g.setColor(secondColour);
g.fillOval ( 15 + (counter*step), 15 + (counter*step), 200 - (counter*2*step) - 10, 200 - (counter*2*step) - 10 );


counter++;
}
}
}
[/highlight]

Color firstColour = new Color(red1, green1, blue1);

You can't just put this line after the constructor and expect it to happen after the constructor is called.

In general the order of things doesn't matter much. If you want to set the value of firstColor based on the values of red1, green1 and blue1 then do that as part of the constructor.

Of course firstColor has to be declared outside the constructor so you can use it elsewhere in the painting method. It is common to group all the declarations together.

Originally Posted by pbrockway2

Color firstColour = new Color(red1, green1, blue1);

In general the order of things doesn't matter much. If you want to set the value of firstColor based on the values of red1, green1 and blue1 then do that as part of the constructor.

Thank you for your reply. I moved the Color declarations to the paint component method and it did work !

Unfortunately (for me) I don't understand why. I did want set the value of the firstColour in the constructor (having declared firstColour outside the constructo - how do I do that? I feel like I'm missing something really fundamental here...

thanks in advance

Thank you for your reply. I moved the Color declarations to the paint component method and it did work !

Unfortunately (for me) I don't understand why. I did want set the value of the firstColour in the constructor (having declared firstColour outside the constructo - how do I do that? I feel like I'm missing something really fundamental here...

thanks in advance

Your algorithm is wrong, that's the reason. The Constructor is invoked but the firstColour and secondColour were already instantiated. So, they "ignore" what you set in your constructor. Compare them with the int-variables you'll see the similarity. Your constructor should be as following:

public DrawBullseye(int r1, int g1, int b1) {
        red1 = r1;
        green1 = g1;
        blue1 = b1;
        firstColour = new Color(red1, green1, blue1);
        secondColour = new Color (red2, green2, blue2);
}
Color firstColour, secondColour;

Thanks, it works & I understand it too !

Originally Posted by veeer

I don't quite know what Voodoo is on about, considering your 'algorithm' (what algorithm?) is not wrong -- I'm not sure quite what he means when he speaks of 'ignoring' what is passed in the constructor. The reality is that you're merely recreating the Color objects every paint with the same components each time, so they turn out to be the same. This is pointless and can be replaced by initializing in the constructor, but both will have the same effect -- though not as Voodoo explained.

Wenn Du nichts verstehst, kannst Du beim Admin beschweren. If you don't understand you can complain at the admin.

Special for veeer,

int red1;
int green1; 
int blue1;
 
int red2 = 99;
int green2 = 182;
int blue2 = 222;
 
 
public DrawBullseye(int r1, int g1, int b1)
{
     red1 = r1;
     green1 = g1;
     blue1 = b1;
}
Color firstColour = new Color(red1, green1, blue1);
....
DrawBullseye target = new DrawBullseye(200,0,0);

Can you tell the forum what firstColour could be after the constructor DrawBullseye(200,0,0) is instanstiated? 0,0,0 or 200,0,0?

Aha,
firstColour = new Color(red1, green1, blue1); is BEFORE red1 = i, etc. That is, my dear schoolmarm !
Or should I call you an uber-schoolteacher? I never intend to write a java book. My answer is usually very short, sometime rude. But I never try to "schoolmarm" anyone, and never demand anyone to stop posting. Are you the owner of this forum? By the way, I never post for a help.

Man, still playing a sniffy schoolmarm,
why should I have to calm down when I'm not "angry"? It's your verbal language that makes you thinking that people are angry. You read something and decide to do something against it without having to understand what was written.
First:

Wenn Du nichts verstehst, kannst Du beim Admin beschweren. If you don't understand you can complain at the admin.

It's so obvious that the English sentence is the translation....only bad people think of evil idea.
Second:

Your algorithm is wrong, that's the reason. The Constructor is invoked but the firstColour and secondColour were already instantiated. So, they "ignore" what you set in your constructor.

public DrawBullseye(int r1, int g1, int b1) {
        red1 = r1;
        green1 = g1;
        blue1 = b1;
        firstColour = new Color(red1, green1, blue1);
        secondColour = new Color (red2, green2, blue2);
}
Color firstColour, secondColour;

What algorithm I talked about, huh? What is an algorithm? Read carefully this passage

More precisely, an algorithm is an effective method expressed as a finite list[1] of well-defined instructions[2] for calculating a function.[3] Starting from an initial state and initial input (perhaps empty),[4] the instructions describe a computation that, when executed, will proceed through a finite [5] number of well-defined successive states, eventually producing "output"[6] and terminating at a final ending state ...Algorithm - Wikipedia, the free encyclopedia.

So, why the steps of the above-mentioned code is not an algorithm and where is the problem?
Sorry, pal. Time-out and game over!

I feel a lock coming on...