A graphical Java program that calculates the MD5 has of it's input.

Hasher.java

import java.awt.*;
import java.awt.event.*;
import java.security.*;
import java.math.*;

/**
 * A graphical Java program that calculates the MD5 has of it's input.
 * @author anroots
 *
 */
public class Hasher {

    Frame window;
    public static void main(String[] args) {
	Hasher md5 = new Hasher();
    }

    /**
     * Build the GUI and display it's contents. Call a method when the button is pressed.
     */
    public Hasher() {
	window = new Frame();
	window.setSize(400,200);
	window.setBackground(Color.pink);
	window.setTitle("MD5 hash generator");

	Label intro = new Label("Enter some text to generate a MD5 hash.");
	intro.setForeground(Color.black);
	TextField input = new TextField(10);
	Button submit = new Button("Generate");

	submit.addActionListener(new ActionListener() {

	    public void actionPerformed(ActionEvent e)
	    {
		String input = ((TextField)((Component)e.getSource()).
			getParent().getComponent (1)).getText();
		((TextField)((Component)e.getSource()).
			getParent().getComponent (1)).setText(hashThis(input));
	    }
	});

	window.setLayout(new GridLayout(3,2));
	window.add(intro);
	window.add(input);
	window.add(submit);
	window.setVisible(true);

    }

    /**
     * Calculates the MD5 hash
     * @param plaintext Input string
     * @return MD5 of plaintext
     */
    private static String hashThis(String plaintext) {
	try {
	    // MD5 calculation code from:
	    //http://stackoverflow.com/questions/415953/generate-md5-hash-in-java/421696#421696
	    MessageDigest m = MessageDigest.getInstance("MD5");
	    m.reset();
	    m.update(plaintext.getBytes());
	    byte[] digest = m.digest();
	    BigInteger bigInt = new BigInteger(1,digest);
	    String hashtext = bigInt.toString(16);
	    // Now we need to zero pad it if you actually want the full 32 chars.
	    while(hashtext.length() < 32 ){
		hashtext = "0"+hashtext;
	    }
	    return hashtext;
	} catch (Exception e) {
	    return "Computation error";
	}
    }
}