rechenmaschine/GUI.java

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class GUI extends JFrame {
    private JPanel panelMain;
    private JTextField textFieldRechenterm;
    private JLabel labelGibRechentermEin;
    private JButton buttonBerechnen;
    private JLabel labelErgebnis;

    public GUI(String title){
        super(title);

        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setContentPane(panelMain);
        this.pack();
        buttonBerechnen.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                //TODO: Text vom Text field zu Eingabe übergeben
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException classNotFoundException) {
                    classNotFoundException.printStackTrace();
                } catch (InstantiationException instantiationException) {
                    instantiationException.printStackTrace();
                } catch (IllegalAccessException illegalAccessException) {
                    illegalAccessException.printStackTrace();
                } catch (UnsupportedLookAndFeelException unsupportedLookAndFeelException) {
                    unsupportedLookAndFeelException.printStackTrace();
                }
                Rechenmaschine rechner = new Rechenmaschine(textFieldRechenterm.getText());
                labelErgebnis.setText("Das Ergebnis ist: "+rechner.getResult());
            }
        });
    }

    public static void main(String[] args) {
        JFrame frame = new GUI("Rechenterme");
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private void createUIComponents() {
        // TODO: place custom component creation code here
    }
}