How to change column width of a table

For the following code, I am not able to set the column size to a custom size. Why is it so?Also the first column is not being displayed.

    import java.awt.BorderLayout;
import java.awt.GridLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTable;
import javax.swing.table.TableColumn;

public class Trial extends JFrame{
   public void create(){
     JPanel jp = new JPanel();
     String[] string = {" ", "A"};
     Object[][] data = {{"A", "0"},{"B", "3"},{"C","5"},{"D","-"}};
     JTable table = new JTable(data, string);     
     jp.setLayout(new GridLayout(2,0));   
     jp.add(table);

     table.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);
     TableColumn column = null;
     for (int i = 0; i < 2; i++) {
        column = table.getColumnModel().getColumn(i);
        column.setPreferredWidth(20);      //custom size
       }
     setLayout(new BorderLayout());
     add(jp);
   }

   public开发者_开发知识库 static void main(String [] a){
      Trial trial = new Trial();
      trial.setSize(300,300);
      trial.setVisible(true);
      trial.setDefaultCloseOperation(Trial.EXIT_ON_CLOSE);
      trial.create();
   }
}

You've got a couple of issues here. First and foremost, Always initialize your JFrame from the Swing EDT as such:

   public static void main(String[] a) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            Trial trial = new Trial();
            trial.setSize(300, 300);
            trial.setDefaultCloseOperation(Trial.EXIT_ON_CLOSE);
            trial.create();
         }
      });
   }

Failure to do so will lead to subtle errors. Second: JTables like to exist within JScrollPanes. That's why you don't see the column headers:

  JScrollPane pane = new JScrollPane();
  pane.setViewportView(table);
  jp.add(pane);

With the above done, I see your tiny little columns, each 20 pixels wide.

When autoresize mode is set to off the column widths will not be adjusted at all when the table is layed out. From JTable's doLayout() documentation:

AUTO_RESIZE_OFF: Don't automatically adjust the column's widths at all. Use a horizontal scrollbar to accomodate the columns when their sum exceeds the width of the Viewport. If the JTable is not enclosed in a JScrollPane this may leave parts of the table invisible.

Try adding the JTable to a JScrollPane and then adding that to the panel.