java - 创建表时 JFrame 中的组件不出现

Question

我是java编程新手。一切进行得都很顺利。但每当创建在 JScrollPane 中调用的 Jtable 时，我的 jframe 似乎都会遇到问题。有时所有组件(例如按钮、标签等)都不会出现。但是当我评论表及其属性时，组件就会出现。我的问题可能是什么？非常感谢您的帮助。多谢!这是我创建表的方法。再次感谢。

package myphonebookbeta;

import java.awt.event.*;
import java.sql.*;
import java.util.ArrayList;
import java.util.Vector;
import java.util.logging.Level;
import java.util.logging.Logger;
 import javax.swing.*;
import javax.swing.table.DefaultTableModel;

public class MainForm extends JFrame implements ActionListener{

//<editor-fold defaultstate="collpased" desc="my components">

JFrame f=new JFrame();
JPanel p=new JPanel(null); 
JLabel fnameLbl,lnameLbl,addressLbl,cpLbl;
JTextField fname,lname,address,cp;
JButton save,delete,cancel,update;
JTable table=null;
JScrollPane scrollPane=null;
JDesktopPane dp=null;
//</editor-fold>

//<editor-fold defaultstate="collapsed" desc="sql variabled">

private final String url="jdbc:mysql://localhost:3306/";
private final String db="dbnetbeans";
private final String uid="root";
private final String pwd="";
private final String driver="com.mysql.jdbc.Driver";
private Connection con=null;
private Statement st=null;
private ResultSet rs;
private ResultSetMetaData md;
private String sql;

//</editor-fold>

public MainForm(){

   mainFormGui();

}//end MainForm

private void mainFormGui(){

   f.setTitle("My Phonebook Beta");
   f.setSize(600,400);
   f.setLocationRelativeTo(f);
   f.setVisible(true);
   f.setDefaultCloseOperation(DO_NOTHING_ON_CLOSE);
   f.addWindowListener(new WindowAdapter(){
       @Override
       public void windowClosing(WindowEvent e){
           int cls=JOptionPane.showOptionDialog(null,"You are about to exit the program! Do you wish to proceed?","WARNING",
                   JOptionPane.YES_NO_OPTION,JOptionPane.WARNING_MESSAGE,null,null,null);
           if (cls==0){
               System.exit(0);
           }
       }
   });

    initComponents();

}//end of mainFormGui

private void initComponents(){

    //<editor-fold defaultstate="collapsed" desc="components declaration">

    fnameLbl=new JLabel("First Name : "); fnameLbl.setBounds(10,18,90,24);
    lnameLbl=new JLabel("Last Name : "); lnameLbl.setBounds(10,52,90,24);
    addressLbl=new JLabel("Address : "); addressLbl.setBounds(10,86,90,24);
    cpLbl=new JLabel("Contact No. :"); cpLbl.setBounds(10,120,90,24);

    fname=new JTextField(""); fname.setBounds(100,14,140,24);
    lname=new JTextField(""); lname.setBounds(100,48,140,24);
    address=new JTextField(""); address.setBounds(100,82,140,24);
    cp=new JTextField(""); cp.setBounds(100,116,140,24);

    save=new JButton("SAVE"); save.setBounds(10,150,110,24);
    cancel=new JButton("Cancel"); cancel.setBounds(130,150,110,24);
    update=new JButton("Update"); update.setBounds(10,180,110,24);
    delete=new JButton("Delete"); delete.setBounds(130,180,110,24);


    //</editor-fold>

    //<editor-fold defaultstate="collapsed" desc="adding to panel">
    p.setVisible(true);

    p.add(fnameLbl); p.add(fname);
    p.add(lnameLbl); p.add(lname);
    p.add(addressLbl); p.add(address);
    p.add(cpLbl); p.add(cp);

    p.add(save);p.add(delete); p.add(update); p.add(cancel);


    //</editor-fold>

    btnAction();

//createTable();

    f.add(p); 


}//end of initComponents

private void btnAction(){
    cancel.addActionListener(this);
    save.addActionListener(this);
    delete.addActionListener(this);

}//end void btnAction

@Override
public void actionPerformed(ActionEvent ae){

    String fn=fname.getText();
    String ln=lname.getText();
    String ad=address.getText();
    String cpn=cp.getText();

    try{

        //<editor-fold defaultstate="collapsed" desc="cancel_click">

        if(ae.getSource()==cancel){

            clearFields();

        }//end cancel

        //</editor-fold>

        //<editor-fold defaultstate="collapsed" desc="save_click">

        if(ae.getSource()==save){

            sql="Insert into tbphonebook (firstname,lastname,address,cp)"
                    + " value('"+fn+"','"+ln+"','"+ad+"','"+cpn+"')";
            connect();
            st=con.createStatement();
            st.executeUpdate(sql);
            disconnect();
            JOptionPane.showMessageDialog(null,"Info successfully SAVED!","confirmation - SAVE ", JOptionPane.INFORMATION_MESSAGE);
            clearFields();

        }//end save

        //</editor-fold>

        //<editor-fold defaultstate="collapsed" desc="delete_click">

        if(ae.getSource()==delete){

            int ch=JOptionPane.showOptionDialog(null,"This action is irrevocable. Do you wish tocontinue?",
                    "Delete this contact?",JOptionPane.YES_NO_OPTION,JOptionPane.WARNING_MESSAGE,null,null,null);

            if (ch==0){

                sql="delete from tbphonebook where firstname like '"+fn+"' and lastname like '"+ln+"'";
                connect();
                st=con.createStatement();
                st.executeUpdate(sql);
                disconnect();
                JOptionPane.showMessageDialog(null,"Contact successfully DELETED!","confirmation - DELETE ", JOptionPane.INFORMATION_MESSAGE);
                clearFields();

            }//end if(ch==0)

        }//end delete

        //</editor-fold>


    }//try

    catch(Exception e){
            e.printStackTrace();
    }//catch
}//end actionPerformed

private void connect(){

   try{
       Class.forName(driver).newInstance();
       con=DriverManager.getConnection(url+db,uid,pwd);
   } 
   catch(Exception ex){
       ex.printStackTrace();
   }


}//end connect

private void disconnect(){

   try{
       con.close();
   } 
   catch(Exception ex){
       ex.printStackTrace();
   }


}//end disconnect   

private void clearFields(){

   fname.setText("");
   lname.setText("");
   address.setText("");
   cp.setText("");
   fname.requestFocus();

}//end clearField

private void createTable(){

    scrollPane=new JScrollPane(this.table);
    scrollPane.setBounds(250,14,320,160);
    scrollPane.setVisible(true); 
    scrollPane.setViewportView(table);
    p.add(scrollPane);

}//end createTable

private void fillTable() throws SQLException{

    ArrayList colNames=new ArrayList();
    ArrayList data=new ArrayList();
    ArrayList row=new ArrayList();

    sql="select * from tbphonebook";
    connect();
    st=con.createStatement();
    rs = st.executeQuery(sql);

    try{

        md =rs.getMetaData();
        int col=md.getColumnCount();

        //to getcolumn names
        for (int i=1;1<=col;i++){
            colNames.add(md.getColumnName(i));
        }

        //to get row data
        while(rs.next()){

            for(int i=1;1<=col;i++){

                row.add(rs.getObject(i));

            }

            data.add(row);
        }

    }
    catch(Exception ex){

        ex.printStackTrace();

    }


}//end fillTable
}

Answer 1

JPanel p=new JPanel(null); 

除非必要，否则不要使用空布局。阅读 this article关于如何使用 GridBagLayout。它易于使用且非常灵活。

关于您的重绘问题:您确定要在 Event Dispatch Thread 上执行该代码吗？ ？