rowWeights and columnWeights

[Lori Battey]

how might one go about accessing and changing these fields of the GridBagLayout class? This isn't working!!
import java.awt.*;
public class GBag extends Panel {
public GBag() {
GridBagConstraints c = new GridBagConstraints();
Font f = new Font("Serif", 0, 36);
setFont(f);
GridBagLayout gbl = new GridBagLayout();
setLayout(gbl);
c.gridx = 0;
c.gridy = 0;
add(new Button("TL"), c);
c.gridx = 1;
add(new Button("Top Middle"), c);
c.gridx = 2;
add(new Button("TR"), c);
// weights
gbl.rowWeights[0] = 1; // NULL POINTER EXCEPTION!!
gbl.columnWeights[0] = 1;
}
public static void main(String args[]) {
Frame f = new Frame("GridBag Example");
f.add(new GBag(), BorderLayout.CENTER);
f.pack();
f.setVisible(true);
}
}

Any help would be appreciated!!
Lori

[Matthew Jones]

Your two lines:

gbl.rowWeights[0] = 1;
gbl.columnWeights[0] = 1;

Should read:

gbl.weightx = 1;
gbl.weighty = 1;

[Lori Battey]

I was trying not to use weightx and weighty per RHE Complete Java Certification (latest edition) on pages 318 and 319. It suggests that rowWeights and columnWeights is a simplified way. I am just not able to find any code examples showing this "simplified" way!
Anyone??
Lori

[Manfred Leonhardt]

Hi Lori,
To use rowWeights you need to actually initialize it and fill it in. It is null double array by default.

  gbl.rowWeights = new double[] {1.};
  gbl.columnWeights = new double[] {1.};

Since you are only setting one value, this approach is not as efficient as just setting the weightx, and weighty GridBagConstraints fields.
Matthew is incorrect in his code change that he gave you since the fields belong to GridBagConstraints and not GridBagLayout!

  c.weightx = 1.0;
  c.weighty = 1.0;

Of course you need to set these before your add the components into your panel. Therefore you will need to move the lines above to the correct location.
Regards,
Manfred.

[Lori Battey]

Great information! Thanks!!
This brings up another question though...should you set rowWeights and columnWeights for each row and column? I know when you set them using weightx and weighty you are specifying which row/column should be the "stretchy" one (I guess you can specify how much "stretchiness" as well). When using rowWeights and columnWeights do you have these same options of setting how much "weight" each row/column has?
Sorry to ask so many questions but I'm brand new to gridBagLayout. Got the other ones down!
Thanks for everyones help! I love JavaRanch!!

[Manfred Leonhardt]

As I understand it, using either will achieve the same results.
Manfred.