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Class ColumnData

This class encapsulates data describing the visual characteristics of a single TableColumn of our table. The instance variables defined in this class have the following meaning:

The only constructor provided assigns each of these variables the data passed as parameters.

Class StockTableData

This class extends AbstractTableModel to serve as the data model for our table. Recall that AbstractTableModel is an abstract class, and three methods must be implemented to instantiate it:

Note: An alternative approach is to extend the DefaultTableModel class which is a concrete implementation of AbstractTableModel. However, this is not recommended, as the few abstract methods in AbstractTableModel can be easily implemented. Usage of DefaultTableModel often creates unnecessary overhead.

By design, this class manages all information about our table, including the title and column data. A static array of ColumnData, m_columns, is provided to hold information about our table's columns (it is used in the StocksTable constructor, see above). Three instance variables have the following meaning:

The only constructor of the StockTableData class initializes two of these variables and calls the setDefaultData() method to assign the pre-defined default data to m_date and m_vector (in a later example we'll see how to use JDBC to retrieve data from a database rather than using hard-coded data as we do here).

As we discussed above, the getRowCount() and getColumnCount() methods should return the number of rows and columns, respectively. So their implementation is fairly obvious. The only catch is that they may be called by the AbstractTableModel constructor before any member variable is initialized. So we have to check for a null instance of m_vector. Note that m_columns, as a static variable, will be initialized before any non-static code is executed (so we don't have to check m_columns against null).

The remainder of the StockTableData class implements the following methods:

Running the Code

Figure 18.1 shows StocksTable in action displaying our hard-coded stock data. Note that the TableColumns resize properly in response to the parent frame size. Also note that the selected row in our table can be moved by changed with the mouse or arrow keys, but no editing is allowed.

18.3 Stocks Table: Part II - Custom Renderers

Now we'll extend StocksTable to use color and small icons in rendering our table cells. To enhance data visibility, we'll make the following two enhancements:

To do this we need to build our own custom TreeCellRenderer.

Click Figure 18.2 for full-scale image. JTable using a custom cell renderer.

The Code: StocksTable.java see \Chapter18\2

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.io.*;
import java.text.*;

import javax.swing.*;
import javax.swing.border.*;
import javax.swing.event.*;
import javax.swing.table.*;

public class StocksTable 
               extends JFrame 
{
  // Unchanged code from 
  //section 18.2

  public StocksTable() {
    // Unchanged code from 
    //section 18.2
        
    for (int k = 0; k < 
      StockTableData.m_columns.length; 
                                k++) {
      DefaultTableCellRenderer 
                   renderer = new 
        ColoredTableCellRenderer();
      renderer.setHorizontalAlignment(
        StockTableData.m_columns[
                      k].m_alignment);
      TableColumn column = 
                    new TableColumn(k, 
        StockTableData.m_columns[
          k].m_width, renderer, null);
      m_table.addColumn(column);   
    }

    // Unchanged code from 
    //section 18.2
  }

  public static void main(String argv[]) {
    new StocksTable();
  }
}

class ColoredTableCellRenderer 
      extends DefaultTableCellRenderer
{
  public void setValue(Object value) {
    if (value instanceof ColorData) {
      ColorData cvalue = (ColorData)value;
      setForeground(cvalue.m_color);
      setText(cvalue.m_data.toString());
    }
    else if (value instanceof IconData) {
      IconData ivalue = (IconData)value;
      setIcon(ivalue.m_icon);
      setText(ivalue.m_data.toString());
    }
    else
      super.setValue(value);
  }
}

class ColorData
{
  public Color  m_color;
  public Object m_data;
  public static Color GREEN = 
                     new Color(0, 128, 0);
  public static Color RED = 
                         Color.red;

  public ColorData(
       Color color, Object data) {
    m_color = color;
    m_data  = data;
  }
    
  public ColorData(Double data) {
    m_color = data.doubleValue() 
            >= 0 ? GREEN : RED;
    m_data  = data;
  }
    
  public String toString() {
    return m_data.toString();
  }
}

class IconData
{
  public ImageIcon  m_icon;
  public Object m_data;

  public IconData(
     ImageIcon icon, Object data) {
    m_icon = icon;
    m_data = data;
  }
    
  public String toString() {
    return m_data.toString();
  }
}

class StockData
{
  public static ImageIcon ICON_UP = 
             new ImageIcon("ArrUp.gif");
  public static ImageIcon ICON_DOWN = 
           new ImageIcon("ArrDown.gif");
  public static ImageIcon ICON_BLANK = 
             new ImageIcon("blank.gif");

  public IconData  m_symbol;
  public String  m_name;
  public Double  m_last;
  public Double  m_open;
  public ColorData  m_change;
  public ColorData  m_changePr;
  public Long    m_volume;

  public StockData(
        String symbol, String name, 
                         double last, 
   double open, double change, double 
             changePr, long volume) {
    m_symbol = 
      new IconData(getIcon(
                     change), symbol);
    m_name = name;
    m_last = new Double(last);
    m_open = new Double(open);
    m_change = new ColorData(
                 new Double(change));
    m_changePr = new ColorData(
               new Double(changePr));
    m_volume = new Long(volume);
  }

  public static ImageIcon 
            getIcon(double change) {
    return (change>0 ? ICON_UP : 
          (change<0 ? ICON_DOWN : 
      ICON_BLANK));
  }
}

// Class StockTableData unchanged 
//from section 18.2

Understanding the Code

Class StocksTable The only change we need to make in the base frame class is to change the column renderer to a new class, ColoredTableCellRenderer. ColoredTableCellRenderer should be able to draw icons and colored text, but not both at the same time---although this could be done using this same approach.

Class ColoredTableCellRenderer

This class extends DefaultTableCellRenderer and overrides only one method: setValue(). This method will be called prior to the rendering of a cell to retrieve its corresponding data (of any nature) as an Object. Our overridden setValue() method is able to recognize two specific kinds of cell data: ColorData, which adds color to a data object, and IconData, which adds an icon (both are described below). If a ColorData instance is detected, its encapsulated color is set as the foreground for the renderer. If an IconData instance is detected, its encapsulated icon is assigned to the renderer with the setIcon() method (which is inherited from JLabel). If the value is neither a ColorData or an IconData instance we call the super-class setValue() method.

Class ColorData

This class is used to bind a specific color, m_color, to a data object of any nature, m_data. Two static ColorsRED and GREEN, are declared to avoid creation of numerous temporary objects. Two constructors are provided for this class. The first constructor takes Color and Object parameters and assigns them to instance variables m_color and m_data respectively. The second constructor takes a Double parameter which gets assigned to m_data, and m_color is assigned the green color if the parameter is positive, and red if negative. The toString() method simply calls the toString() method of the data object.

Class IconData

This class is used to bind ImageIcon m_icon to a data object of any nature, m_data. Its only constructor takes ImageIcon and Object parameters. The toString() method simply calls the toString() method of the data object.

Class StockData

This class has been enhanced from its previous version to to provide images and new variable data types. We've prepared three static ImageIcon instances holding images: arrow up, arrow down, and a blank, all transparent image. The static getIcon() method returns one of these images depending on the sign of the given double parameter. We've also changed three instance variables to bind data with the color and image attributes according to the following table:

The corresponding changes are also required in the StockData constructor.

Running the Code

Figure 18.2 shows StocksTable with custom rendering in action. Note the correct usage of color and icons, which considerably enhances the visualization of our data.

Improving visual communication Tables can be data intensive and consequently it can be very difficult for the viewer to quickly pick out the important information. The table in fig 18.1 highlighted this. In fig 18.2, we are improving the visual communication with the introduction of visual layers. The icons in the first column quickly tell the viewer whether a price is rising or falling. This is visually re-inforced with the red and green introduced on the change columns.

Red particularly is a very strong color. By introducing red and green only on the change columns and not across the entire row, we avoid the danger of the red becoming overpowering. If we had introduced red and green across the full width of the table, the colors may have become intrusive and impaired the visual communication.

18.4Stocks Table: part III - Data Formatting

To further enhance the presentation of our stock data, in this section we wll take into account that actual stock prices (at least on NYSE and NASDAQ) are expressed in fractions of 32, not in decimals. Another issue that we will deal with is the volume of trade, which can reach hundreds of millions of dollars. Volume is not immediately legible without separating thousands and millions places with commas.

Figure 18.3 JTable with custom number formatting cell renderer to display fractions and comma-delimited numbers.

The Code: StocksTable.java

see \Chapter18\3

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.io.*;
import java.text.*;

import javax.swing.*;
import javax.swing.border.*;
import javax.swing.event.*;
import javax.swing.table.*;

// Unchanged code from 
//section 18.3

class Fraction
{
  public int m_whole;
  public int m_nom;
  public int m_den;

  public Fraction(double value) {
    int sign = value <0 ? -1 : 1;
    value = Math.abs(value);
    m_whole = (int)value;
    m_den = 32;
    m_nom = (int)((value-m_whole)*m_den);
    while (m_nom!=0 && m_nom%2==0) {
      m_nom /= 2;
      m_den /= 2;
    }
    if (m_whole==0)
      m_nom *= sign;
    else
      m_whole *= sign;
  }

  public double doubleValue() {
    return (double)m_whole + 
             (double)m_nom/m_den;
  }

  public String toString() {
    if (m_nom==0)
      return ""+m_whole;
    else if (m_whole==0)
      return ""+m_nom+"/"+m_den;
    else
      return ""+m_whole+" 
               "+m_nom+"/"+m_den;
  }
}

class SmartLong
{
  protected static 
         NumberFormat FORMAT;

  static {
    FORMAT = 
     NumberFormat.getInstance();
    FORMAT.setGroupingUsed(true);
  }

  public long m_value;

  public SmartLong(long value) 
            { m_value = value; }

  public long longValue() 
            { return m_value; }

  public String toString() 
              { return FORMAT.format(
                          m_value); }
}

class ColorData
{
  public ColorData(Fraction data) {
    m_color = data.doubleValue() 
                 >= 0 ? GREEN : RED;
    m_data  = data;
  }

  // Unchanged code from section 18.3
}

class StockData
{
  public static ImageIcon ICON_UP = 
               new ImageIcon("ArrUp.gif");
  public static ImageIcon ICON_DOWN = 
             new ImageIcon("ArrDown.gif");
  public static ImageIcon ICON_BLANK = 
               new ImageIcon("blank.gif");

  public IconData  m_symbol;
  public String  m_name;
  public Fraction  m_last;
  public Fraction  m_open;
  public ColorData  m_change;
  public ColorData  m_changePr;
  public SmartLong  m_volume;

  public StockData(String symbol, 
                     String name, 
                      double last, 
   double open, double change, 
     double changePr, long volume) {
    m_symbol = 
       new IconData(getIcon(
                change), symbol);
    m_name = name;
    m_last = new Fraction(last);
    m_open = new Fraction(open);
    m_change = new ColorData(
            new Fraction(change));
    m_changePr = new ColorData(
            new Double(changePr));
    m_volume = new SmartLong(volume);
  }

  // Unchanged code from section 18.3
}

Understanding the Code

Class Fraction

This new data class encapsulates fractions with denominator 32 (or in a reduced form). Three instance variables represent the whole number, numerator, and denominator of the fraction. The only constructor takes a double parameter and carefully extracts these values, performing numerator and denominator reduction, if possible. Note that negative absolute values are taken into account.

Method doubleValue() performs the opposite task: it converts the fraction into a double value. Method toString() forms a String representation of the fraction.

Note that a zero whole number or a zero nominator are omitted to avoid unseemly output like "0 1/2" or "12 0/32".

Class SmartLong

This class encapsulates long values. The only constructor takes a long as parameter and stores it in the m_value instance variable. The real purpose of creating this class is the overridden toString() method, which inserts commas separating thousands, millions, etc. places. For this purpose we use the java.text.NumberFormat class. An instance of this class is created as a static variable, and formatting values using NumberFormat's format() method couldn't be easier.

Note: SmartLong cannot extend Long (although it would be natural), because java.lang.Long is a final class.

Note: We could use the different approach of just formatting the initial contents of our table's cells into text strings and perating on them without introducing new data classes. This approach, however, is not desirable from a design point of view, as it strips the data of its true nature: numbers.

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