将JPanel添加到JFrame

Question

我正在尝试将此 JPanel 添加到 JFrame 中，但我看不到他。当我创建新的 java 类并自己制作这个框架时，一切都很好。

来自JFrame表单的代码。

   public class MainFrame extends javax.swing.JFrame

{

/**
 * Creates new form MainFrame
 */
public MainFrame()
{
    this.getContentPane().add(firstPanel);
    initComponents();
}

/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents()
{

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 400, Short.MAX_VALUE)
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 300, Short.MAX_VALUE)
    );

    pack();
}// </editor-fold>                        

/**
 * @param args the command line arguments
 */
public static void main(String args[])
{
    /* Set the Nimbus look and feel */
    //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
    /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
     * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
     */
    try
    {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels())
        {
            if ("Nimbus".equals(info.getName()))
            {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex)
    {
        java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex)
    {
        java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex)
    {
        java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex)
    {
        java.util.logging.Logger.getLogger(MainFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>

    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable()
    {
        public void run()
        {
            new MainFrame().setVisible(true);
        }
    });
}

// Variables declaration - do not modify                     
// End of variables declaration                   
FirstPanel firstPanel =  new FirstPanel();
}

来自 JPanel 的代码：

public class FirstPanel extends javax.swing.JPanel
{

/**
 * Creates new form FirstPanel
 */
public FirstPanel()
{
    initComponents();
}

/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents()
{

    jButton1 = new javax.swing.JButton();

    setBackground(new java.awt.Color(0, 0, 0));

    jButton1.setText("jButton1");

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(this);
    this.setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
            .addContainerGap(164, Short.MAX_VALUE)
            .addComponent(jButton1)
            .addGap(155, 155, 155))
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGap(129, 129, 129)
            .addComponent(jButton1)
            .addContainerGap(145, Short.MAX_VALUE))
    );
}// </editor-fold>                        


// Variables declaration - do not modify                     
private javax.swing.JButton jButton1;
// End of variables declaration                   
}

来自Java类的代码。

  public class mainn extends JFrame

{
   public mainn()
   {    this.setSize(700,600);
       this.getContentPane().add(firstPanel);
   }
    FirstPanel firstPanel = new FirstPanel();
public static void main(String args[])
{

    java.awt.EventQueue.invokeLater(new Runnable()
    {
        @Override
        public void run()
        {
            new mainn().setVisible(true);
        }
    });
}
}

我想不出区别在哪里。有人能帮我吗？

Answer 1

您还必须在JPanel上调用setVisible（true）。