Java-Code

import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class ZahlenSysteme {
	public static void main(String[] args) {

		FrZahlenSysteme frZahlenSysteme = new FrZahlenSysteme("Umrechnung von Zahlensystemen");
	}
}

class FrZahlenSysteme extends JFrame implements ActionListener {
	JLabel lbEingabe = new JLabel("Zahl eingeben: ");
	JTextField tfEingabe = new JTextField(21);
	JButton bOK = new JButton("    OK    ");
	JLabel lbBinaer = new JLabel("binaer: ");
	JTextField tfBinaer = new JTextField(21);
	JLabel lbOktal = new JLabel("oktal: ");
	JTextField tfOktal = new JTextField(21);
	JLabel lbHexadezimal = new JLabel("hexadezimal: ");
	JTextField tfHexadezimal = new JTextField(21);
	JPanel pEingabe = new JPanel();
	JPanel pOK = new JPanel();
	JPanel pBinaer = new JPanel();
	JPanel pOktal = new JPanel();
	JPanel pHexadezimal = new JPanel();

	FrZahlenSysteme(String titel) {
		super(titel);
		setVisible(true);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setBounds(300, 300, 420, 420);
		setMinimumSize(new Dimension(380, 400));
		setLayout(new GridLayout(5, 1));

		tfEingabe.setHorizontalAlignment(JTextField.RIGHT);
		tfBinaer.setHorizontalAlignment(JTextField.RIGHT);
		tfOktal.setHorizontalAlignment(JTextField.RIGHT);
		tfHexadezimal.setHorizontalAlignment(JTextField.RIGHT);

		tfBinaer.setEditable(false);
		tfOktal.setEditable(false);
		tfHexadezimal.setEditable(false);

		pEingabe.setLayout(new FlowLayout(FlowLayout.RIGHT, 30, 10));
		pOK.setLayout(new FlowLayout(FlowLayout.RIGHT, 30, 10));
		pBinaer.setLayout(new FlowLayout(FlowLayout.RIGHT, 30, 10));
		pOktal.setLayout(new FlowLayout(FlowLayout.RIGHT, 30, 10));
		pHexadezimal.setLayout(new FlowLayout(FlowLayout.RIGHT, 30, 10));

		pEingabe.add(lbEingabe);
		pEingabe.add(tfEingabe);
		pOK.add(bOK);
		pBinaer.add(lbBinaer);
		pBinaer.add(tfBinaer);
		pOktal.add(lbOktal);
		pOktal.add(tfOktal);
		pHexadezimal.add(lbHexadezimal);
		pHexadezimal.add(tfHexadezimal);

		add(pEingabe);
		add(pOK);
		add(pBinaer);
		add(pOktal);
		add(pHexadezimal);

		bOK.addActionListener(this);
		tfEingabe.addActionListener(this);
	}

	public void berechneZahl(String stEingabe) {
		StringBuilder sbBinaer = new StringBuilder();
		StringBuilder sbOktal = new StringBuilder();
		StringBuilder sbHexadezimal = new StringBuilder();
		int dezimal;
		int binaer;
		int oktal;
		int hexadezimal;
		boolean plus = true;

		try {
			dezimal = Integer.parseInt(stEingabe);
			if (dezimal == 0) {
				tfBinaer.setText("0");
				tfOktal.setText("0");
				tfHexadezimal.setText("0");
			} else {
				if (dezimal < 0) {
					dezimal = dezimal * (-1);
					plus = false;
				}
				binaer = oktal = hexadezimal = dezimal;
				while (binaer != 0) {
					if (binaer % 2 == 0) {
						sbBinaer.append(0);
						binaer = binaer / 2;
					} else {
						sbBinaer.append(1);
						binaer = (binaer - 1) / 2;
					}

					while (oktal != 0) {
						if (oktal % 8 == 0) {
							sbOktal.append(0);
							oktal = oktal / 8;
						} else {
							sbOktal.append(oktal % 8);
							oktal = (oktal - oktal % 8) / 8;
						}
					}
					while (hexadezimal != 0) {
						if (hexadezimal % 16 == 0) {
							sbHexadezimal.append(0);
							hexadezimal = hexadezimal / 16;
						} else {
							if (hexadezimal % 16 <= 10) {
								sbHexadezimal.append(hexadezimal % 16);
							} else if (hexadezimal % 16 == 10) {
								sbHexadezimal.append('A');
							} else if (hexadezimal % 16 == 11) {
								sbHexadezimal.append('B');
							} else if (hexadezimal % 16 == 12) {
								sbHexadezimal.append('C');
							} else if (hexadezimal % 16 == 13) {
								sbHexadezimal.append('D');
							} else if (hexadezimal % 16 == 14) {
								sbHexadezimal.append('E');
							} else if (hexadezimal % 16 == 15) {
								sbHexadezimal.append('F');
							}
							hexadezimal = (hexadezimal - hexadezimal % 16) / 16;

						}
					}
				}
				sbBinaer.reverse();
				sbOktal.reverse();
				sbHexadezimal.reverse();
				if (plus == true) {
					tfBinaer.setText(sbBinaer.toString());
					tfOktal.setText(sbOktal.toString());
					tfHexadezimal.setText(sbHexadezimal.toString());
				}
				if (plus == false) {
					tfBinaer.setText("-" + sbBinaer.toString());
					tfOktal.setText("-" + sbOktal.toString());
					tfHexadezimal.setText("-" + sbHexadezimal.toString());
				}
			}

		} catch (NumberFormatException e) {
			tfBinaer.setText("Ganze Zahl eingeben bis 2.000.000.000!");
			tfOktal.setText("");
			tfHexadezimal.setText("");
		}
	}

	@Override
	public void actionPerformed(ActionEvent evt) {
		berechneZahl(tfEingabe.getText());

	}
}