Diverse udvidelser til kode

Hej

jeg har gang i noget kode, og det virker også fint
men jeg vil gerne lave nogle udvidelser:

1.)  Hvis felterne er NULL skal de sættes til 0
2.)  Resultatet skal retuneres med 3 decimaler.

Så hvordan kan jeg gøre dette ?

## Koden ##


/**
@Author: Claus Joergensen
@date 19. August 2004
*/

import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import java.io.*;
import java.net.*;
import javax.swing.*;

public class GridBagDemo extends JFrame {

      JLabel overskrift = new JLabel( " Indtast a,b & c " );
      JTextField inputA = new JTextField(4);
      JTextField inputB = new JTextField(4);
      JTextField inputC = new JTextField(4);
      JLabel underskrift = new JLabel( " Antal Nulpunkter " );
      JLabel blank = new JLabel("\n");
      JLabel blank2 = new JLabel("\n");
      JTextField antalNP = new JTextField(4);
      JLabel xValues = new JLabel( " X-værdier" );
      JTextField xPlus = new JTextField(2);
      JTextField xMinus = new JTextField(2);
      JButton udregnKnap = new JButton("Udregn !");

  public GridBagDemo() {
      super( "GridBagLayout" );

      Container container = getContentPane();
      GridBagLayout layout = new GridBagLayout();
      container.setLayout(layout);
      GridBagConstraints constraints = new GridBagConstraints();

      constraints.fill = GridBagConstraints.BOTH;
      constraints.gridx = 0;
      constraints.gridy = 0;
      constraints.gridwidth = 3;
      constraints.gridheight = 8;

      constraints.fill = GridBagConstraints.HORIZONTAL;
      constraints.gridx = 0;
      constraints.gridy = 0;
      constraints.gridwidth = 3;
      constraints.gridheight = 1;

      layout.setConstraints(overskrift,constraints);    // Tilføjer overskriften
      container.add(overskrift);

/*********** START INPUTS **********************************************/

      constraints.fill = GridBagConstraints.BOTH;
      constraints.gridx = 0;
      constraints.gridy = 1;
      constraints.gridwidth = 1;
      constraints.gridheight = 1;

      layout.setConstraints(inputA,constraints);  // Add inputA
      container.add(inputA);

      constraints.fill = GridBagConstraints.BOTH;
      constraints.gridx = 1;
      constraints.gridy = 1;
      constraints.gridwidth = 1;
      constraints.gridheight = 1;

      layout.setConstraints(inputB,constraints);  // Add inputB
      container.add(inputB);

      constraints.fill = GridBagConstraints.BOTH;
      constraints.gridx = 2;
      constraints.gridy = 1;
      constraints.gridwidth = 1;
      constraints.gridheight = 1;

      layout.setConstraints(inputC,constraints);  // Add inputC
      container.add(inputC);

/*********** END INPUTS *********** Start Nulpunkter *******************/
     
      constraints.fill = GridBagConstraints.BOTH;
      constraints.gridx = 0;
      constraints.gridy = 2;
      constraints.gridwidth = 3;
      constraints.gridheight = 1;

      layout.setConstraints(blank,constraints);  // Blank space
      container.add(blank);


      constraints.fill = GridBagConstraints.BOTH;
      constraints.gridx = 0;
      constraints.gridy = 3;
      constraints.gridwidth = 1;
      constraints.gridheight = 1;

      layout.setConstraints(underskrift,constraints);  // Add nulpunks lablet
      container.add(underskrift);

      constraints.fill = GridBagConstraints.HORIZONTAL;
      constraints.gridx = 1;
      constraints.gridy = 3;
      constraints.gridwidth = 2;
      constraints.gridheight = 1;

      layout.setConstraints(antalNP,constraints);  // Add antal nulpunker
      container.add(antalNP);

      constraints.fill = GridBagConstraints.BOTH;
      constraints.gridx = 0;
      constraints.gridy = 4;
      constraints.gridwidth = 3;
      constraints.gridheight = 1;

      layout.setConstraints(blank2,constraints);  // Blank space
      container.add(blank2);
     
/*********** END nulpunker *********** Start xværdier *******************/

      constraints.fill = GridBagConstraints.BOTH;
      constraints.gridx = 0;
      constraints.gridy = 5;
      constraints.gridwidth = 1;
      constraints.gridheight = 1;

      layout.setConstraints(xValues,constraints);  // Add antal en label mere
      container.add(xValues);

      constraints.fill = GridBagConstraints.BOTH;
      constraints.gridx = 0;
      constraints.gridy = 6;
      constraints.gridwidth = 1;
      constraints.gridheight = 1;

      layout.setConstraints(xPlus,constraints);  // x+
      container.add(xPlus);

      constraints.fill = GridBagConstraints.BOTH;
      constraints.gridx = 0;
      constraints.gridy = 7;
      constraints.gridwidth = 1;
      constraints.gridheight = 1;

      layout.setConstraints(xMinus,constraints);  // x-
      container.add(xMinus);

      constraints.fill = GridBagConstraints.BOTH;
      constraints.gridx = 1;
      constraints.gridy = 6;
      constraints.gridwidth = 2;
      constraints.gridheight = 2;

      layout.setConstraints(udregnKnap,constraints);  // Knappen som udregner resultatet.
      container.add(udregnKnap);

      udregnKnap.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent evt) {
      udregnKnapActionPerformed(evt);
      }
        }
      );

      setSize( 250, 270 );
      setVisible( true );
  }


  private void udregnKnapActionPerformed(ActionEvent evt) {
  double a = Integer.parseInt(inputA.getText());
  double b = Integer.parseInt(inputB.getText());
  double c = Integer.parseInt(inputC.getText());

  double xPlusRes = (-b + (Math.sqrt((b*b)-4*a*c))) / (a * 2);
  String xPlusString = String.valueOf(xPlusRes);
  xPlus.setText(xPlusString);

  double xMinusRes = (-b - (Math.sqrt((b*b)-4*a*c))) / (a * 2);
  String xMinusString = String.valueOf(xMinusRes);
  xMinus.setText(xMinusString);


  }

  public static void main( String args[] )  {
      GridBagDemo application = new GridBagDemo();
      application.setDefaultCloseOperation(
              JFrame.EXIT_ON_CLOSE );
  }

}