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javaswingjtable

How do I make a JTable column size exactly (or closely) fit contents?

The output from my program is in a JTextArea inside a JScrollPane. It looks nasty:

Created BinaryTree.java      in     I:\Netbeans OLDIES but KEEPIES\BinaryTree\src\binarytree\BinaryTree.java
Created DisplayStuff.java        in     I:\Netbeans OLDIES but KEEPIES\BinaryTree\src\binarytree\DisplayStuff.java
Created LinkedList.java      in     I:\Netbeans OLDIES but KEEPIES\BinaryTree\src\binarytree\LinkedList.java
Created Node.java        in     I:\Netbeans OLDIES but KEEPIES\BinaryTree\src\binarytree\Node.java
Created notes        in     I:\Netbeans OLDIES but KEEPIES\BinaryTree\src\binarytree\notes
Created TryBinaryTree.java       in     I:\Netbeans OLDIES but KEEPIES\BinaryTree\src\binarytree\TryBinaryTree.java

So I thought about putting the output into a JTable, assuming it would be a simple matter to adjust column size at the end of execution and get results that look more like a spreadsheet and thus be more readable:

enter image description here

I'd never used JTable before, so I tried a simple program to see if I could make a JTable at all. I did. Here it is:

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.WindowConstants;
import javax.swing.table.DefaultTableModel;
import javax.swing.table.TableColumnModel;

public class TestJTable 
{
  static void init()
  {
    fraFrame = new JFrame();
    fraFrame.setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);

        dftTableModel = new DefaultTableModel(0 , 4);
        tblOutput     = new JTable(dftTableModel);
        scrOutput     = new JScrollPane(tblOutput);
        colMdl        =     tblOutput.getColumnModel();

    fraFrame.add(scrOutput); // NOTE: add the SCROLL PANE, not table
    fraFrame.setVisible(true);
    fraFrame.pack();
  }

  public static void main(String[] args) 
  {
    init();
    tblOutput.doLayout();
    dftTableModel.addRow(new Object[]{"Action", "Filename", "", "Path"});
    for (int i = 0; i < 100; i++) 
    {
        String c0 = Utilities.Utilities.repeat("x", (int) (Math.random()*50));
        dftTableModel.addRow(new Object[]{((Math.sin(i)) > 0 ? "Updated" : "Created"), 
                                          c0, "in", c0});
        k = Math.max(k, c0.length());
    }
  }
  static int                  k;
  static JFrame               fraFrame ;
  static JTable               tblOutput; 
  static DefaultTableModel    dftTableModel; 
  static JScrollPane          scrOutput;
  static TableColumnModel     colMdl;
}

And here's the output:

enter image description here

I want to be able to set the columns' sizes exactly as I want.

An hour of spinning my wheels with sizes, preferred sizes, table sizes, autoresizing (and not) led me to try the following in varying combinations at varying parts of the program, none producing satisfactory results, although taking out pack helped somewhat:

    fraFrame.setSize(1400, 600);
    tblOutput.setSize(1500,400);
    colMdl.getColumn(0).setPreferredWidth(15);
    colMdl.getColumn(1).setPreferredWidth(10*k);
    colMdl.getColumn(2).setPreferredWidth(5);
    colMdl.getColumn(3).setPreferredWidth(10*k);

So it is that I have to ask:

(a) Specifically, given that I know that k is the number of characters in the Filename and 'Pathcolumns, how can I make the contents of those columns be exactly fit their columns? (I assumefont` size will enter the picture.)

(b) Generally, how do I change the column size in a JTable? E.g., one column will always say "in". How to make the column be no wider than that?

EDIT

Thanks to @camickr, it was EASY to get the desired output, both in the test program above and in the real thing, output below:

enter image description here

Solution

  • Check out the Table Column Adjuster.

    You can set the column width based on:

    1. the heading of the column
    2. the data in each row of the column
    3. the larger of the heading or data

    The class also supports other features to allow for dynamic resizing if the data is changed.

    Or you can use the basic code provided which just uses the prepareRenderer(...) method of the JTable to determine the maximum width.

    JTable table = new JTable( ... );
table.setAutoResizeMode( JTable.AUTO_RESIZE_OFF );

for (int column = 0; column < table.getColumnCount(); column++)
{
    TableColumn tableColumn = table.getColumnModel().getColumn(column);
    int preferredWidth = tableColumn.getMinWidth();
    int maxWidth = tableColumn.getMaxWidth();

    for (int row = 0; row < table.getRowCount(); row++)
    {
        TableCellRenderer cellRenderer = table.getCellRenderer(row, column);
        Component c = table.prepareRenderer(cellRenderer, row, column);
        int width = c.getPreferredSize().width + table.getIntercellSpacing().width;
        preferredWidth = Math.max(preferredWidth, width);

        //  We've exceeded the maximum width, no need to check other rows

        if (preferredWidth >= maxWidth)
        {
            preferredWidth = maxWidth;
            break;
        }
    }

    tableColumn.setPreferredWidth( preferredWidth );
}

    Edit:

    I was hoping that knowing the font size and number of characters 

    FontMetrics fm = table.getFontMetrics( table.getFont() );
int charWidth = fm.stringWidth("a");
System.out.println( charWidth );