java - 从 Java 类调用对象以在单独的表单上显示的代码不起作用，为什么？

Question

我在 NetBeans 中创建了一个空白的 Swing GUI。然后，我创建了一个单独的 Java 类 (empClass)，其中包含我想要在 Swing 表单(员工)上显示的所有对象(按钮、文本框、标签等)。表单的设计将有一个面板，其中包含一系列标签和文本框，用于运算符(operator)工信息。面板外部有两个按钮，一个位于表单顶部作为标题的标签，以及一个 JList。我已经创建了类中的所有对象，并且根据在线研究，将类中的对象调用到 Swing 窗体上的所有必要编码都是正确的，但是当我运行应用程序时，窗体保持空白，并且不显示在其他类。我怎样才能让它发挥作用？

下面是 Swing Form(员工)中调用 Java 类的代码:

public class employees extends javax.swing.JFrame {


    public employees() {
        initComponents();

       this.setPreferredSize(new Dimension(720,520));

       this.add(ec.getpanel());


    }

    empClass ec = new empClass(); 

这是java类(empClass)的完整编码:

package SV_Operations;

import java.awt.*;
import javax.swing.*;

public class empClass 
{
    public JButton bfunction = new javax.swing.JButton("Add");
    public JButton cancel = new javax.swing.JButton("Cancel");
    public JList empList = new javax.swing.JList();
    public JLabel picon = new javax.swing.JLabel();
    public ImageIcon icon = new ImageIcon(empClass.class.getResource("/Pictures/Carbon.jpg"));    
    public JPanel panel = new javax.swing.JPanel();  
    public JLabel lbltitle = new javax.swing.JLabel("Admin Page");
    public JLabel lblemp = new javax.swing.JLabel("Employee ID: ");
    public JTextField txtempid = new javax.swing.JTextField();
    public JLabel lblidno = new javax.swing.JLabel("ID Number:");
    public JTextField txtidno = new javax.swing.JTextField();
    public JLabel lblname = new javax.swing.JLabel("Name:");
    public JTextField txtname = new javax.swing.JTextField();
    public JLabel lblsurname = new javax.swing.JLabel("Surname: ");
    public JTextField txtsurname = new javax.swing.JTextField();
    public JLabel lblcell = new javax.swing.JLabel("Cellphone no: ");
    public JTextField txtcell = new javax.swing.JTextField();
    public JLabel lblalt = new javax.swing.JLabel("Alternative no: ");
    public JTextField txtalt = new javax.swing.JTextField();
    public JLabel lblemail = new javax.swing.JLabel("Emial: ");
    public JTextField txtemail = new javax.swing.JTextField();
    public JLabel lbladdress = new javax.swing.JLabel("Address: ");
    public JTextField txtaddress = new javax.swing.JTextField();
    public JLabel lblpass = new javax.swing.JLabel("Password: ");
    public JTextField txtpass = new javax.swing.JTextField();


    public empClass()
    {

    }


    public JPanel getpanel()
    {
        return panel;
    }

    public void layoutUI()
    {

        panel.setLayout(null);
        panel.setBorder(javax.swing.BorderFactory.createBevelBorder(javax.swing.border.BevelBorder.RAISED));
        panel.setBounds(230, 80, 450, 310);
        panel.setBorder(javax.swing.BorderFactory.createBevelBorder(javax.swing.border.BevelBorder.RAISED));
        panel.setLayout(null);
        panel.setVisible(true);
        panel.add(panel);

        lbltitle.setFont(new java.awt.Font("Excelerate", 1, 42));
        lbltitle.setBounds(60, 0, 620, 70);
        lbltitle.setForeground(Color.RED);


        lblemp.setFont(new java.awt.Font("Alexis", 1, 18));
        lblemp.setBounds(45, 30, 170, 13);
        lblemp.setForeground(Color.RED);
        lblemp.setVisible(true);
        panel.add(lblemp);

        txtempid.setBounds(200, 20, 230, 30);
        txtempid.setVisible(true);
        panel.add(txtempid);

        lblidno.setFont(new java.awt.Font("Alexis", 1, 18));
        lblidno.setBounds(72, 60, 170, 13);
        lblidno.setForeground(Color.RED);
        lblidno.setVisible(true);
        panel.add(lblidno);

        txtidno.setBounds(200, 50, 230, 30);
        txtidno.setVisible(true);
        panel.add(txtidno);

        lblname.setFont(new java.awt.Font("Alexis", 1, 18));
        lblname.setBounds(131, 90, 180, 13);
        lblname.setForeground(Color.RED);
        lblname.setVisible(true);
        panel.add(lblname);

        txtname.setBounds(200, 80, 230, 30);
        txtname.setVisible(true);
        panel.add(txtname);

        lblsurname.setFont(new java.awt.Font("Alexis", 1, 18));
        lblsurname.setBounds(85, 120, 180, 13);
        lblsurname.setForeground(Color.RED);
        lblsurname.setVisible(true);
        panel.add(lblsurname);

        txtsurname.setBounds(200, 110, 230,13);
        txtsurname.setVisible(true);
        panel.add(txtsurname);

        lblcell.setFont(new java.awt.Font("Alexis", 1, 18));
        lblcell.setBounds(34, 150, 190, 13);
        lblcell.setForeground(Color.RED);
        lblcell.setVisible(true);
        panel.add(lblcell);

        txtcell.setBounds(200, 140, 230, 30);
        txtcell.setVisible(true);
        panel.add(txtcell);

        lblalt.setFont(new java.awt.Font("Alexis", 1, 18));
        lblalt.setBounds(18, 180, 190, 13);
        lblalt.setForeground(Color.RED);
        lblalt.setVisible(true);
        panel.add(lblalt);

        txtalt.setBounds(200, 170, 230, 30);
        txtalt.setVisible(true);
        panel.add(txtalt);

        lblemail.setFont(new java.awt.Font("Alexis", 1, 18));
        lblemail.setBounds(129, 210, 190, 13);
        lblemail.setForeground(Color.RED);
        lblemail.setVisible(true);
        panel.add(lblemail);

        txtemail.setBounds(200, 200, 230, 30);
        txtemail.setVisible(true);
        panel.add(txtemail);

        lbladdress.setFont(new java.awt.Font("Alexis", 1, 18));
        lbladdress.setBounds(92, 240, 190, 13);
        lbladdress.setForeground(Color.RED);
        lbladdress.setVisible(true);
        panel.add(lbladdress);

        txtaddress.setBounds(200, 260, 230, 30);
        txtaddress.setVisible(true);
        panel.add(txtaddress);

        lblpass.setFont(new java.awt.Font("Alexis", 1, 18));
        lblpass.setBounds(75, 270, 190, 13);
        lblpass.setForeground(Color.RED);
        lblpass.setVisible(true);
        panel.add(lblpass);

        txtpass.setBounds(200, 260, 230, 30);
        txtpass.setVisible(true);
        panel.add(txtpass);

        picon.setBounds(0, 0, 450, 310);
        picon.setIcon(icon);
        picon.setVisible(true);
        panel.add(picon);

        empList.setBounds(20, 80, 190, 300);
        empList.setModel(new javax.swing.AbstractListModel()
        {
            String[]strings = {"EMP123", "EMP124", "EMP125"};
            public int getSize() {return strings.length;}
            public Object getElementAt(int i) {return strings [i];}
        });
        empList.setVisible(true);


        bfunction.setBounds(230, 400, 150, 39);
        bfunction.setVisible(true);


        bfunction.addActionListener(new java.awt.event.ActionListener()
        {
            @Override
            public void actionPerformed(java.awt.event.ActionEvent evt)
            {
                b1ActionPerformed(evt);
            }
        });

        cancel.setBounds(530, 400, 150, 39);
        cancel.setVisible(true);


        cancel.addActionListener(new java.awt.event.ActionListener()
        {
            @Override
            public void actionPerformed(java.awt.event.ActionEvent evt)
            {
                cancelActionPerformed(evt);
            }
        });


    }

    private void b1ActionPerformed(java.awt.event.ActionEvent evt)
    {
        //Left blank for now
    }

    private void cancelActionPerformed(java.awt.event.ActionEvent evt)
    {
        System.exit(0);
    }
}

Answer 1

这是因为您忘记调用 empClass 类的构造函数中的方法。

所以你的构造函数将是:

public empClass()
{
    layoutUI(); // you forgot this line!
}

但是使用 null 布局根本不合适。专业人士不使用空布局。当您使用 null 作为布局管理器时，您将失去的最重要的功能是调整框架大小。请参阅 GridBagLayout 教程，我非常喜欢它，因为我发现它是最可定制的。您还可以了解其他布局管理器，如 GroupLayout、BorderLayout、FlowLayout、GridLayout 等，以及混合它们以创建专业设计的方式。

祝你好运