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Swing Chapter 18. (Advanced topics) Tables. Easy for reading, Click here!

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Swing Chapter 18. (Advanced topics) Tables. Easy for reading, Click here!

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Page: 3/9 



Previous Page Previous Page (2/9) - Next Page (4/9) Next Page
Subpages: 1. JTable  
2.
Stocks Table: part I - Basic JTable example 
3.
Stocks Table: part II - Custom renderers 
4. Stocks Table: part III - Data formatting 
5. Stocks Table: part IV - Sorting columns 
6.
Stocks Table: part V - JDBC
7.
Stocks Table: part VI - Column addition and removal
8.
Expense report application
9.
JavaBeans property editor

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:

Render absolute and percent changes in green for positive values and red for negative values.

Add an icon next to each stock symbol: arrow up for positive changes and arrow down for negative.

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

Figure 18.2 JTable using a custom cell renderer.

<<file figure18-2.gif>>

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 Colors, RED 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:

Field                       New type                Data object            Description

m_symbol           IconData           String                Stock's symbol (NYSE or NASDAQ)

m_change           ColorData        Double                Absolute change in price

m_changePr     ColorData        Double                Percent change in price

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.

UI Guideline : 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.



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