Java-Code

package bmi;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

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

public class BMI {

	public static double calculation(double gewicht, double groesse) {
		return gewicht / Math.pow(groesse / 100, 2);
	}

	public static String valuation(double input) {

		String output = null;

		if (input < 16 && input > 0) {
			output = "Starkes Untergewicht";
		} else if (input >= 16 && input < 17) {
			output = "Mäßiges Untergewicht";
		} else if (input >= 17 && input < 18.5) {
			output = "Leichtes Untergewicht";
		} else if (input >= 18.5 && input < 25) {
			output = "Normalgewicht";
		} else if (input >= 25 && input < 30) {
			output = "Präadipositas";
		} else if (input >= 30 && input < 35) {
			output = "Adipositas Grad I";
		} else if (input >= 35 && input < 40) {
			output = "Adipositas Grad II";
		} else if (input >= 40) {
			output = "Adipositas Grad III";
		} else if (input < 0) {
			output = "ERROR";
		}

		return output;
	}

	public static void showUI() {

		JFrame frame = new JFrame();
		BoxLayout layout = new BoxLayout(frame.getContentPane(), BoxLayout.PAGE_AXIS);
		JButton okButton = new JButton();
		JTextField inputFieldGewicht = new JTextField();
		JTextField inputFieldGroesse = new JTextField();
		JTextField outputField = new JTextField();

		JLabel gewicht = new JLabel("Gewicht:");
		JLabel groesse = new JLabel("Größe:");

		frame.setSize(300, 180);
		frame.setLayout(layout);

		frame.add(groesse);
		frame.add(inputFieldGroesse);
		frame.add(gewicht);
		frame.add(inputFieldGewicht);
		frame.add(okButton);
		frame.add(outputField);

		outputField.setEditable(false);

		okButton.setText("Bestätigen");

		okButton.addActionListener(new ActionListener() {
			@Override
			public void actionPerformed(ActionEvent e) {
				double output = calculation(Integer.parseInt(inputFieldGewicht.getText()),
						Integer.parseInt(inputFieldGroesse.getText()));
				outputField.setText(valuation(output));
			}
		});

		frame.setLocationRelativeTo(null);
		frame.setVisible(true);

	}

	public static void main(String[] args) {
		showUI();
	}
}