Computer Science 523
Advanced Programming

Summer 2014, The College of Saint Rose

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PrimeFactors Demo

A working demo of PrimeFactors will appear below. Click inside the applet to interact with it.

PrimeFactors BlueJ Project

Click here to download a BlueJ project for PrimeFactors.

PrimeFactors Source Code

The Java source code for PrimeFactors is below. Click on a file name to download it.

PrimeFactors.java

/*
 * Example PrimeFactors: use a JApplet to compute prime factorizations
 *
 * Jim Teresco, The College of Saint Rose, CSC 523, Summer 2014
 *
 * $Id: PrimeFactors.java 2379 2014-06-17 03:52:55Z terescoj $
 */

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import javax.swing.JApplet;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class PrimeFactors extends JApplet implements ActionListener {
    
    // need to remember our JTextField for use in the event handler
    private JTextField numberField;
    // and we'll be updating this JLabel with results
    private JLabel factorLabel;
    
    public void init() {
        
        Container contentPane = getContentPane();
        
        setSize(500, 150);
        
        // set up our dialog window
        JPanel topPanel = new JPanel();
        
        topPanel.add(new JLabel("Number to factor: "));
        // create a text field with 10 visible characters
        numberField = new JTextField("", 10);
        topPanel.add(numberField);
        numberField.addActionListener(this);
        JButton button = new JButton("Factor It!");
        topPanel.add(button);
        button.addActionListener(this);
        
        contentPane.add(topPanel, BorderLayout.NORTH);
        
        factorLabel = new JLabel("Results will appear here.");
        contentPane.add(factorLabel, BorderLayout.CENTER);
        
        contentPane.validate();
        
        
    }
    
    // a helper method that clears the field and resets the label
    private void reset() {
    
        factorLabel.setText("Results will appear here.");
        numberField.setText("");
    }
    
    // handle the button press OR enter in the text field 
    // but since we do the same thing in either case, we 
    // don't care which one triggered it
    public void actionPerformed(ActionEvent e) {
        
        // first, we'll try to convert the String in the text field to an int,
        // and if the conversion fails we'll get a NumberFormatException thrown
        int number;
        String s = numberField.getText();
        try {
            number = Integer.parseInt(s);
        }
        catch (NumberFormatException ex) {
            JOptionPane.showMessageDialog(null, "Could not convert " + s + " to an integer.", 
                                          "Error", JOptionPane.ERROR_MESSAGE);
            reset();
            return;
        }
        
        // so we have a number -- is it factorable?
        if (number < 2) {
            JOptionPane.showMessageDialog(null, "Number must be at least 2.", 
                                          "Error", JOptionPane.ERROR_MESSAGE);
            reset();
            return;
        }
        
        // it is a good one - let's factor it in a straightforward way
        ArrayList<Integer> factors = new ArrayList<Integer>();
        int remaining = number;
        // factor the 2's
        while (remaining % 2 == 0) {
            factors.add(2);
            remaining /= 2;
        }
        // now try odd factors -- we could try only primes but it's probably
        // harder to figure out the primes than to just try the odd non-primes
        for (int tryFactor = 3; tryFactor <= remaining; tryFactor += 2) {
            while (remaining % tryFactor == 0) {
                factors.add(tryFactor);
                remaining /= tryFactor;
            }
        }
        
        // so we have an ArrayList of the factors, let's put them into our label
        factorLabel.setText("Prime factors of " + number + " are: " + factors);
        numberField.setText("");
    }
}