用类生成JFormattedTextField

Question

我在这里遇到了麻烦，我试图创建一个创建JFormattedTextFields的类，它可以工作，但是我需要获得它的价值，那就是我得到NullPointerExeption的时候，有我的代码：

JDialog：

package br.edu.faculdadedosguararapes;

import java.awt.EventQueue;

import javax.swing.JDialog;
import javax.swing.JPanel;
import javax.swing.border.TitledBorder;
import javax.swing.border.EtchedBorder;
import javax.swing.JFormattedTextField;
import javax.swing.SwingConstants;

import java.awt.Dialog.ModalityType;
import java.awt.FlowLayout;
import java.awt.Color;

import javax.swing.JTextField;
import javax.swing.JButton;

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

public class Det4x4 extends JDialog {

    private JFormattedTextField aL1C1;
    private JFormattedTextField aL1C2;
    private JFormattedTextField aL1C3;
    private JFormattedTextField aL1C4;
    private JFormattedTextField aL2C1;
    private JFormattedTextField aL2C2;
    private JFormattedTextField aL2C3;
    private JFormattedTextField aL2C4;
    private JFormattedTextField aL3C1;
    private JFormattedTextField aL3C2;
    private JFormattedTextField aL3C3;
    private JFormattedTextField aL3C4;
    private JFormattedTextField aL4C1;
    private JFormattedTextField aL4C2;
    private JFormattedTextField aL4C3;
    private JFormattedTextField aL4C4;
    private JTextField tfDeterminante;
    private GeraObjeto textField;

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    Det4x4 dialog = new Det4x4();
                    dialog.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
                    dialog.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public Det4x4() {
        setTitle("Matriz 4x4");
        setModalityType(ModalityType.APPLICATION_MODAL);
        setResizable(false);
        setBounds(100, 100, 487, 362);
        getContentPane().setLayout(null);

        JPanel panel = new JPanel();
        panel.setBorder(new TitledBorder(new EtchedBorder(EtchedBorder.LOWERED, null, null), "Matriz", TitledBorder.CENTER, TitledBorder.TOP, null, null));
        panel.setBounds(12, 12, 143, 130);
        getContentPane().add(panel);
        panel.setLayout(new FlowLayout(FlowLayout.CENTER, 5, 5));

        textField = new GeraObjeto();

        textField.novoFtf(aL1C1, panel);
        textField.novoFtf(aL1C2, panel);
        textField.novoFtf(aL1C3, panel);
        textField.novoFtf(aL1C4, panel);

        textField.novoFtf(aL2C1, panel);
        textField.novoFtf(aL2C2, panel);
        textField.novoFtf(aL2C3, panel);
        textField.novoFtf(aL2C4, panel);

        textField.novoFtf(aL3C1, panel);
        textField.novoFtf(aL3C2, panel);
        textField.novoFtf(aL3C3, panel);
        textField.novoFtf(aL3C4, panel);

        textField.novoFtf(aL4C1, panel);
        textField.novoFtf(aL4C2, panel);
        textField.novoFtf(aL4C3, panel);
        textField.novoFtf(aL4C4, panel);

        JPanel panelDet = new JPanel();
        panelDet.setBorder(new TitledBorder(new EtchedBorder(EtchedBorder.LOWERED, null, null), "Determinante", TitledBorder.CENTER, TitledBorder.TOP, null, new Color(0, 0, 0)));
        panelDet.setBounds(12, 169, 125, 52);
        getContentPane().add(panelDet);

        tfDeterminante = new JTextField();
        tfDeterminante.setHorizontalAlignment(SwingConstants.CENTER);
        tfDeterminante.setEditable(false);
        tfDeterminante.setColumns(5);
        panelDet.add(tfDeterminante);

        JButton btnCalcular = new JButton("Calcular");
        btnCalcular.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {

                int a[][] = new int[4][4];  
                //CalculaDet determinante = new CalculaDet();

                a[0][0] = Integer.parseInt(textField.getFtfContent(aL1C1));
                /*a[0][1] = Integer.parseInt(textField.getFtfContent(aL1C2));
                a[0][2] = Integer.parseInt(textField.getFtfContent(aL1C3));
                a[0][3] = Integer.parseInt(textField.getFtfContent(aL1C4));
                a[1][0] = Integer.parseInt(textField.getFtfContent(aL2C1));
                a[1][1] = Integer.parseInt(textField.getFtfContent(aL2C2));
                a[1][2] = Integer.parseInt(textField.getFtfContent(aL2C3));
                a[1][3] = Integer.parseInt(textField.getFtfContent(aL2C4));             
                a[2][0] = Integer.parseInt(textField.getFtfContent(aL3C1));
                a[2][1] = Integer.parseInt(textField.getFtfContent(aL3C2));
                a[2][2] = Integer.parseInt(textField.getFtfContent(aL3C3));
                a[2][3] = Integer.parseInt(textField.getFtfContent(aL3C4));
                a[3][0] = Integer.parseInt(textField.getFtfContent(aL4C1));
                a[3][1] = Integer.parseInt(textField.getFtfContent(aL4C2));
                a[3][2] = Integer.parseInt(textField.getFtfContent(aL4C3));
                a[3][3] = Integer.parseInt(textField.getFtfContent(aL4C4));*/

                tfDeterminante.setText(String.valueOf(a[0][0]));

                //determinante.Determinante(a[0][0], a[0][1], a[0][2], a[1][0], a[1][1], a[1][2], a[2][0], a[2][1], a[2][2],
                    //  tfDiagonalPrincipal, tfDiagonalSecundaria, tfDeterminante);
            }
        });

        btnCalcular.setBounds(187, 154, 99, 23);
        getContentPane().add(btnCalcular);

        JButton btnLimpar = new JButton("Limpar");
        btnLimpar.setBounds(187, 189, 99, 23);
        getContentPane().add(btnLimpar);


    }
}

类：

package br.edu.faculdadedosguararapes;

import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

import javax.swing.JFormattedTextField;
import javax.swing.JPanel;
import javax.swing.SwingConstants;

public class GeraObjeto {

        public JFormattedTextField novoFtf(JFormattedTextField nome, JPanel panel, int bound1, int bound2){
            nome = new JFormattedTextField();
            nome.setBounds(bound1, bound2, 22, 20);
            nome.setHorizontalAlignment(SwingConstants.CENTER);
            nome.setColumns(2);
            nome.addKeyListener(new KeyAdapter() {
                @Override
                public void keyTyped(KeyEvent arg0) {
                    char c = arg0.getKeyChar();
                    if (!(Character.isDigit(c) || (c==KeyEvent.VK_BACK_SPACE) || c==KeyEvent.VK_DELETE || Character.toString(c).equals("-"))){
                        arg0.consume();
                    }
                }
            });

            panel.add(nome);
            return nome;
        }

        public JFormattedTextField novoFtf(JFormattedTextField nome, JPanel panel){
            nome = new JFormattedTextField();
            nome.setHorizontalAlignment(SwingConstants.CENTER);
            nome.setColumns(2);
            nome.addKeyListener(new KeyAdapter() {
                @Override
                public void keyTyped(KeyEvent arg0) {
                    char c = arg0.getKeyChar();
                    if (!(Character.isDigit(c) || (c==KeyEvent.VK_BACK_SPACE) || c==KeyEvent.VK_DELETE || Character.toString(c).equals("-"))){
                        arg0.consume();
                    }
                }
            });

            panel.add(nome);
            return nome;
        }

        public String getFtfContent(JFormattedTextField nome){
            return nome.getText();
        }

}

为了测试，我注释了一些行，并尝试获取其中一个文本字段的值，但我得到了：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at br.edu.faculdadedosguararapes.GeraObjeto.getFtfContent(GeraObjeto.java:50)
    at br.edu.faculdadedosguararapes.Det4x4$2.actionPerformed(Det4x4.java:110)

我确信，我需要的是创建一种方法来设置JFT的值，但我现在不知道如何设置。

Answer 1

您正在创建一个新的JFormattedTextField，但是没有将新对象分配给类所持有的变量，因此所有变量都为null。实际上，您正在将对象赋值给novoFtf方法的参数，该方法不会自动将其分配给类所持有的JFormattedTextField变量。我想你可以：

aL1C1 = textField.novoFtf(aL1C1, panel);

其他问题：

• 您的代码似乎不必要地复杂，使调试变得困难。我会重构和简化。
• 如果您需要一个字段网格，使用一个数组或ArrayList，这将有助于我上面的建议，简化。
• 您正在使用setBounds和null布局。我建议您不要这样做，因为这使得GUI变得非常不灵活，虽然它们在一个平台上看起来很好，但在大多数其他平台或屏幕分辨率上看起来很糟糕，而且很难更新和维护。相反，您需要学习和学习布局管理器，然后嵌套JPanels，每个布局管理器都使用自己的布局管理器来创建令人愉悦和复杂的GUI，这些GUI在所有操作系统上看起来都很不错。
• 例如，矩阵字段应该由一个使用4乘4 JPanel的GridLayout保存，这个JPanel可以放在使用GridBagLayout的主JPanel中。
• 避免将KeyListener与JTextComponent (如JTextField或JFormattedTextField )一起使用，因为这会导致重大且难以调试的问题。还有更好的方法来做这类事情，包括使用DocumentListener，DocumentFilter，InputVerifier.