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Thread: object not accessible

  1. #1
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    Default object not accessible

    /* hi guys.When i am willing to generate an event by clicking the button b1 to write text in textfield t1,there is an exception.t1 is not accessible in action listener class.I even declared t1 as public but in vain.Please help.*/
     
    import java.io.*;
    import java.lang.*;
    import java.util.*;
    import java.awt.*;
    import javax.swing.*;
    import java.awt.event.*;
     
    class mynew extends JFrame
    {
     
      public mynew()
     {
     
      super("MyFrame");
      setSize(200,200);
      JPanel row1=new JPanel();
      JCheckBox c1=new JCheckBox("yeah",true);
      JCheckBox c2=new JCheckBox("nay",false);
      JPanel row2=new JPanel();
      JLabel l1=new JLabel("Name:",JLabel.RIGHT);
      JTextField t1=new JTextField();
      JTextField t11=new JTextField("Mohd.fazal");
      JTextField t111=new JTextField("Mohd.fazal");
      JLabel l2=new JLabel("Class:",JLabel.RIGHT);
      JTextField t12=new JTextField("Mohd.Shahid");
      JTextField t2=new JTextField("B.E.3rd Year");
      JTextField t112=new JTextField("Mohd.fazal");
      JLabel l3=new JLabel("RollNO:",JLabel.RIGHT);
      JTextField t3=new JTextField("Number 52");
      JTextField t13=new JTextField("Mohd.Shahid");
      JTextField t113=new JTextField("Mohd.fazal");
     
      JPanel row3=new JPanel();
      JButton B1=new JButton("B1");
      JButton B2=new JButton("B2");
      JButton B3=new JButton("B3");
      row3.setBackground(Color.yellow);
      JPanel row4=new JPanel();
      JButton B4=new JButton("B4");
      JButton B5=new JButton("B5");
      JButton B6=new JButton("B6");  
      row4.setBackground(Color.yellow);
      JPanel row5=new JPanel();
      JButton B7=new JButton("B7");
      JButton B8=new JButton("B8");
      JButton B9=new JButton("B9");  
      row5.setBackground(Color.yellow);
     
      Container pane=getContentPane();
      pane.setBackground(Color.red);
      GridLayout lm=new GridLayout(5,1,10,10);
      pane.setLayout(lm);
     
      FlowLayout f1=new FlowLayout(FlowLayout.CENTER,10,10);
      row1.setLayout(f1);
      row1.add(c1);
      row1.add(c2);
      pane.add(row1);
     
     
      GridLayout g1=new GridLayout(3,3,10,10);
      row2.setLayout(g1);
      row2.add(l1);
      row2.add(t1);
      row2.add(t11);
       row2.add(t111);
      row2.add(l2);
      row2.add(t2);
      row2.add(t12);
       row2.add(t112);
      row2.add(l3);
      row2.add(t3);
      row2.add(t13);
       row2.add(t113);
      pane.add(row2);
     
     
      FlowLayout g2=new FlowLayout(FlowLayout.CENTER,10,10);
      row3.setLayout(g2);
      row3.add(B1);
      row3.add(B2);
      row3.add(B3);
      pane.add(row3);
     
      FlowLayout g3=new FlowLayout(FlowLayout.CENTER,10,10);
      row4.setLayout(g3);
      row4.add(B4);
      row4.add(B5);
      row4.add(B6);
      pane.add(row4);
     
      FlowLayout g4=new FlowLayout(FlowLayout.CENTER,10,10);
      row5.setLayout(g4);
      row5.add(B7);
      row5.add(B8);
      row5.add(B9);
      pane.add(row5);
     
      B1.addActionListener(new sd());
      B2.addActionListener(new sd());
      B3.addActionListener(new sd());
      B4.addActionListener(new sd());
      B5.addActionListener(new sd());
      B6.addActionListener(new sd());
      B7.addActionListener(new sd());
      B8.addActionListener(new sd());
      B9.addActionListener(new sd());
     
     
     
      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      setVisible(true);
     }
    } 
     
    class sd implements ActionListener
    {
     
     public void actionPerformed(ActionEvent e)
     {
      String se=e.getActionCommand();
      try
      {
       t1.setText("You pressed "+se);
      }
      catch(Exception ex)
      {
       System.out.println("Error"); 
      }
     }
    }
     
    public class mynew1
    {
     
     public static void main(String[] arguments)throws Exception
     {
     
      mynew obj=new mynew();
     }
    }
    Last edited by helloworld922; February 22nd, 2010 at 07:27 PM.


  2. #2
    Super Moderator helloworld922's Avatar
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    Default Re: object not accessible

    There is no way for another class to reference an object it has no knowledge of (ie. in another class). You must somehow pass that object to your sd class. Also, as a side note in this case it isn't necessary to create a new action listener for each component. This makes your code somewhat sloppy and also wastes memory.

    public class sd
    {
         private JTextField field;
         public sd(JTextField textField)
         {
              this.field = textField;
         }
     
         public void actionPerformed(ActionEvent e)
         {
              String se = e.getActionCommand();
              try
              {
                   t1.setText("You pressed " + se);
              }
              catch (Exception ex)
              {
                   System.out.println("Error");
              }
         }
    }

    // where adding the action listener
    sd actionListener = new sd(t1);
    B1.addActionListener(actionListener);
    B2.addActionListener(actionListener);
    B3.addActionListener(actionListener);
    B4.addActionListener(actionListener);
    B5.addActionListener(actionListener);
    B6.addActionListener(actionListener);
    B7.addActionListener(actionListener);
    B8.addActionListener(actionListener);
    B9.addActionListener(actionListener);

    As a side note, I would strongly recommend choosing variable names that would be meaningful not only to you, but also to others who would read your code. Choose names that represent what that variable contains, being descriptive yet some-what brief. See the variable names I chose as an example.

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