Eclipse Java 8 Error: Label cannot be resolved

Question

I am trying to program an 'Inch-to-Centimeter Calculator'. I've got a problem with the method umrechnen(). The label lblCenti cannot be resolved. My Code is equal to the Solutioncode. I am grateful for every answer or tip I get.

I don't know what I should add to my Description, but StackOverflow forces me to write more, so I'm writing this.

package gui;

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.text.DecimalFormat;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.JButton;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

public class ZollZentimeter extends JFrame {

    private JPanel contentPane;
    private JTextField tfInch;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    ZollZentimeter frame = new ZollZentimeter();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public ZollZentimeter() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 359, 157);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(null);

        JButton btnCalculate = new JButton("Umrechnen");
        btnCalculate.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                umrechnen();
            }
        });
        btnCalculate.setBounds(12, 77, 116, 25);
        contentPane.add(btnCalculate);

        JButton btnEnde = new JButton("Ende");
        btnEnde.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                System.exit(0);
            }
        });
        btnEnde.setBounds(214, 77, 116, 25);
        contentPane.add(btnEnde);

        JLabel lblZoll = new JLabel("Zoll");
        lblZoll.setBounds(12, 13, 56, 16);
        contentPane.add(lblZoll);

        tfInch = new JTextField();
        tfInch.addKeyListener(new KeyAdapter() {
            @Override
            public void keyPressed(KeyEvent e) {
                if(e.getKeyCode()==KeyEvent.VK_ENTER){
                    umrechnen();
                }
            }
        });

        JLabel lblCenti = new JLabel("");
        lblCenti.setBounds(214, 42, 116, 22);
        contentPane.add(lblCenti);
        tfInch.setBounds(12, 42, 116, 22);
        contentPane.add(tfInch);
        tfInch.setColumns(10);

        }

        private void umrechnen(){
            DecimalFormat f=new DecimalFormat("#0.00");
            double z, cm;
            z=Double.parseDouble(tfInch.getText());
            cm=z*2.54;
            lblCenti.setText(f.format(cm+" cm"));
            tfInch.requestFocus();
            tfInch.selectAll();
        }
}

Answer 1

JLabel lblCenti = new JLabel("");

"lblCenti" is defined as a local variable so it can only be accessible in the method/constructor where you define it.

It you want to access the label in another method you need to define it as an instance variable, the same way you do with the "tfInch" variable.