Question

My code is for an applet that expands a binomial. I haven’t finished it, but it’ll only accept an exponent between 1 and 10, inclusive. I got it to 7, but like I said, I haven’t finished. My problem is this: in the first textField, it’ll accept a number and a variable (like 4a, or something). And the code I wrote can’t take into account that number (it’s supposed to only accept a variable). So…How do I get it so that the first textField can’t allow there to be an int? THANKS!

import java.applet.Applet; 
import java.awt.*;
import java.awt.event.*; 
import java.applet.*; 
import javax.swing.*; 
import java.text.DecimalFormat; 
import java.util.ArrayList; 
import javax.swing.Action;

public class BinomialExpander extends JApplet implements ActionListener
{
  JLabel welcome;
  JLabel directions;
  JLabel example;

  JLabel instructions;
  JLabel startOfBinomial;
  JLabel plusSign;
  JLabel forExponent;
  JLabel endOfBinomial;

  JTextField firstVar;
  JTextField txtSecond;
  JTextField exp;


  JLabel lblExpanded; 
  JLabel outputExpanded;  
  FlowLayout layout;

  JButton compute;

  private int[] pascal1 = {1,1};
  private int[] pascal2 = {1,2,1};
  private int[] pascal3 = {1,3,3,1};
  private int[] pascal4 = {1,4,6,4,1};
  private int[] pascal5 = {1,5,10,10,5,1};
  private int[] pascal6 = {1,6,15,20,15,6,1};
  private int[] pascal7 = {1,7,21,35,35,21,7,1};
  private int[] pascal8 = {1,8,28,56,70,56,28,8,1};
  private int[] pascal9 = {1,9,36,84,126,84,36,9,1};
  private int[] pascal10 = {1,10,45,120,210,120,45,10,1};

  private String a;
  private int y; 
  private int expo;
  private String x;

  public void init() 
  {
      Container c = getContentPane(); 
      c.setBackground(Color.pink);

      layout = new FlowLayout();
      layout.setAlignment(FlowLayout.LEFT);
      c.setLayout(layout);
      setSize(500,175);

      welcome = new JLabel("Welcome to the Binomial Expander Applet!");
      welcome.setFont(new Font("Copperplate Gothic Bold", Font.PLAIN, 16));
      directions = new JLabel("Enter binomial ONLY in the form: (VARIABLE + NUMBER)^EXPONENT");
      directions.setFont(new Font("Times New Roman", Font.PLAIN, 14));
      example = new JLabel("EXAMPLE: (x + 2)^2.");
      instructions = new JLabel("Enter the variable of your binomial:");
      startOfBinomial = new JLabel(" (");
      firstVar = new JTextField(4);
      plusSign = new JLabel(" + ");
      txtSecond = new JTextField(4);
      endOfBinomial = new JLabel(")");
      forExponent = new JLabel("^");
      forExponent.setFont(new Font("Times New Roman", Font.PLAIN, 10));
      exp = new JTextField(2);
      compute = new JButton("Compute!");
      compute.addActionListener(this);
      lblExpanded = new JLabel("Your expanded binomial is: ");
      outputExpanded = new JLabel("");
      c.add(welcome);
      c.add(directions);
      c.add(example);
      c.add(instructions);
      c.add(startOfBinomial);
      c.add(firstVar);
      c.add(plusSign);
      c.add(txtSecond);
      c.add(endOfBinomial);
      c.add(forExponent);
      c.add(exp);
      c.add(compute);
      c.add(lblExpanded);
      c.add(outputExpanded);
  }
  public void actionPerformed(ActionEvent event) 
  {
      a = firstVar.getText();
      y = Integer.parseInt(txtSecond.getText());
      expo = Integer.parseInt(exp.getText());

      outputExpanded.setText(expand()); 
  }
  public String expand()
  {  
     if (expo < 1 || expo > 10)
     {
        x = "ERROR: Exponent value must be between 1 and 10, inclusive.";
        return x;
     }
     else if (expo == 1)
     {
        x = a + "+" + y;
        return x;  
     }
     else if (expo == 2)
     {
        x = a + "^" + expo + " + " + (pascal2[1] * y) + a + " + " + (pascal2[2] * Math.pow(y, expo));
        return x;
     }
     else if (expo == 3)
     {
        x = a + "^" + expo + " + " + (pascal3[1] * y) + a + "^" + (expo-1) + (pascal3[2] * Math.pow(y, expo-1)) + a + " + " + (Math.pow(y, expo));
        return x;
     }
     else if (expo == 4)
     {
        x = a + "^" + expo + " + " + (pascal4[1] * y) + a + "^" + (expo-1) + " + " + (pascal4[2] * Math.pow(y, expo-2)) + a + " ^ " + (expo-2) + " + " + (pascal4[3] * 
        Math.pow(y, expo-1)) + a + "+" + (Math.pow(y,expo));
        return x;
     }
     else if (expo == 5)
     {
        x = a + "^" + expo + " + " + (pascal5[1] * y) + a + "^" + (expo-1) + " + " + (pascal5[2] * Math.pow(y,expo-3)) + a + "^" + (expo-2) + " + " + (pascal5[3] * 
        Math.pow(y, expo-2)) + a + "^" + (expo-3) + " + " + (pascal5[4] * Math.pow(y, expo-1)) + a + " + " + (Math.pow(y, expo));
        return x;
     }
     else if (expo == 6)
     {
        x = a + "^" + expo + " + " + (pascal6[1] * y) + a + "^" + (expo-1) + " + " + (pascal6[2] * Math.pow(y, expo-4)) + a + "^" + (expo-2) + " + " + (pascal6[3] *
        Math.pow(y, expo-3)) + a + "^" + (expo-3) + " + " + (pascal6[4] * Math.pow(y, expo-2)) + a + "^" + (expo-4) + " + " + (pascal6[5] * Math.pow(y, expo-1)) +
        a + " + " + (Math.pow(y,expo));
        return x;
     }
     else if (expo == 7)
     {
        x = a + "^" + expo + " + " + (pascal7[1] * y) + a + "^" + (expo-1) + " + " + (pascal7[2] * Math.pow(y, expo-5)) + a + "^" + (expo-2) + " + " + (pascal7[3]
        * Math.pow(y, expo-4)) + a + "^" + (expo-3) + " + " + (pascal7[4] * Math.pow(y, expo-3)) + a + "^" + (expo-4) + " + " + (pascal7[5] * Math.pow(y, expo-2))
        + a + "^" + (expo-5) + (pascal7[6] * Math.pow(y, expo-1)) + a + " + " + (Math.pow(y, expo));
        return x;
     }
     return x; 
  }
  }

Answer 1

I would recommend using String's match() function to see if the value in a is a valid answer (I don’t know what is valid for you). and then if it’s not valid you can use a JDialog to show an error message rather than computing the binomial.

It would looks something like this:

  public void actionPerformed(ActionEvent event) 
  {
      a = firstVar.getText();
      y = Integer.parseInt(txtSecond.getText());
      expo = Integer.parseInt(exp.getText());

      if(a.matches(/*Some REGEX*/)) {
          outputExpanded.setText(expand());
      }
      else {
          //Use the JDialog
      } 
  }

Here are the pages:

String

JDialog