java - Eclipse Java 8 错误 : Label cannot be resolved

Question

我正在尝试编写一个“英寸到厘米计算器”。我的 umrechnen() 方法有问题。无法解析标签 lblCenti。我的代码等于解决方案代码。我很感激我得到的每一个答案或提示。

我不知道应该在描述中添加什么，但 StackOverflow 迫使我写更多内容，所以我写了这篇文章。

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” 被定义为本地 变量，因此只能在定义它的方法/构造函数中访问它。

如果您想在另一种方法中访问标签，则需要将其定义为实例变量，就像使用“tfInch”变量一样。