为什么while（rs.next（））显示文本框中的最后一个值

Question

我想创建一个在线考试项目。当我点击下一步它应该显示下一个数据在textarea.but问题是当我点击提交按钮它显示来自数据库的最新数据（rs.next（））打印文本框中的最后一个值。

import java.awt.BorderLayout; 

    import java.awt.GridLayout; 

    import java.awt.event.ActionEvent; 

    import java.awt.event.*; 

    import javax.swing.*; 

    import java.sql.*; 

    import java.awt.*; 

    import java.util.*; 



    class Abc extends JFrame implements ActionListener{ 

    JLabel l1,l2,l3,l4; 
    JButton b1,b2; 
    JTextArea j1,j2; 
    JCheckBox c1,c2,c3,c4; 
    ButtonGroup group=new ButtonGroup(); 

    JPanel panel2; 
    Abc(){ 
     j1=new JTextArea(); 
     j2=new JTextArea(); 
     c1=new JCheckBox(); 
     c2=new JCheckBox(); 
     c3=new JCheckBox(); 
     c4=new JCheckBox(); 
     j1.setEditable(false); 
     c1.setSelected(false); 
     c2.setSelected(false); 
     c3.setSelected(false); 
     c4.setSelected(false); 

     group.add(c1); 
     group.add(c2); 
     group.add(c3); 
     group.add(c4); 

     Connection conn=null; 
     try{ 
      Class.forName("oracle.jdbc.driver.OracleDriver"); 
     conn=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe","system","java"); 
     System.out.println("Dc is obtained"); 

      } 
     catch(Exception e2){ 
     System.out.println("conne"+e2.getMessage()); 
      } 
     try{ 
      String sq="select * from questionans"; 
      Statement st=conn.createStatement(); 
      ResultSet rs=st.executeQuery(sq); 
      System.out.println("------------------------------------------"); 
      if(rs.next()) 
      { 

      j1.setText(rs.getString(2)); 
      c1.setText(rs.getString(3)); 
      c2.setText(rs.getString(4)); 
      c3.setText(rs.getString(5)); 
      c4.setText(rs.getString(6)); 
      } 
      System.out.println("-------------------------------------------");   
      } 
      catch(Exception e1){ 
      System.out.println("query" +e1.getMessage()); 
      } 
     finally{ 
      try { 
       conn.close(); 
       } 
      catch(Exception e) 
      { 
      System.out.println("close conn"+e.getMessage());  
      } 
      } 








     b1=new JButton("REGISTER"); 
     b2=new JButton("SUBMIT"); 
     panel2=new JPanel(new GridLayout(4,1)); 
     panel2.add(b1); 
     panel2.add(j1); 
     panel2.add(c1); 
     panel2.add(c2); 
     panel2.add(c3); 
     panel2.add(c4); 
     panel2.add(b2); 

     add(panel2,BorderLayout.CENTER); 
     b1.addActionListener(this); 
     b2.addActionListener(this); 
     setTitle("REGISTRATION"); 

     } 
     public void actionPerformed(ActionEvent e) { 
      Object source=e.getSource(); 
      if(source==b1) 
      { 
       System.out.println("you pressed button b1"); 
       } 
       else if(source==b2) 
       { 

       Connection conn=null; 

       try{ 
        Class.forName("oracle.jdbc.driver.OracleDriver"); 
     conn=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe","system","java"); 
        System.out.println("Dc is obtained"); 

        } 
      catch(Exception e4){ 
        System.out.println("conne"+e4.getMessage()); 
        } 
       try{ 
        String sq="select * from questionans"; 
        Statement st=conn.createStatement(); 
        ResultSet rs=st.executeQuery(sq); 
        System.out.println("------------------------------------------"); 



       while(rs.next()){ 

        j1.setText(rs.getString(2)); 
        c1.setText(rs.getString(3)); 
        c2.setText(rs.getString(4)); 
        c3.setText(rs.getString(5)); 
        c4.setText(rs.getString(6)); 

        } 



        System.out.println("-------------------------------------------");   
        } 
      catch(Exception e3){ 
        System.out.println("query" +e3.getMessage()); 
        } 
      finally{ 
        try{ 
         conn.close(); 
         } 
      catch(Exception e6) 
        { 
        System.out.println("close conn"+e6.getMessage());  
        } 
        } 

      String s2=""; 
      if(c1.isSelected()){ 
        s2=s2+""+c1.getText(); 
        } 
      else if(c2.isSelected()){ 
        s2=s2+""+c2.getText(); 
        } 
      else if(c3.isSelected()){ 
     s2=s2+""+c3.getText(); 
     } 
    else if(c4.isSelected()){ 
     s2=s2+""+c4.getText(); 
     } 


System.out.println("You clicked on "+s2); 
} 
    } 

} 


class xyz 
{ 
public static void main(String args[]) 
{ 
    Abc a=new Abc(); 
    a.setSize(1000,1000) ; 
    a.setVisible(true); 
    a.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 

} 

} 

Answer 1

我不清楚你的问题。无论如何，你循环db表中的所有数据直到最后一个数据，并在while循环中设置了setText。这意味着循环结束时在文本框中设置最后一个数据。