Java Tips Weblog

Wouldn’t it be nice to be able to edit the values in a JList? Well a list was designed to be display only so it would involve a major rewrite of the component to support this requirement. For this reason, the most common suggestion found in the forums is to create a single column JTable and use it as a list. This is a very powerfull solution as you inherit all the default rendering and editing capabilities of a table. But what if you just want simple editing of the values, is there another way?
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You have a JComboBox on a crowded form and there is no room to display a label describing the usage of the combo box. Or, maybe you just don’t want to use a label. In either case, you need to display a prompt message in the combo box indicating its usage. One way to do this is to simply use the first item of the combo box as the prompt message and then make this item the selected item. But what if you don’t want the prompt message to be part of the combo box drop down?
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You may want to use a JTextArea or JTextPane as a simple console type component. That is, messages from your application will be added to the console as they are generated. Now you will probably need the ability to limit the total number of messages in the console so that you don’t run out of memory. How can we do this?
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Many Swing components support the concept of invoking an Action when a certain event occurs. For example, clicking on a button will invoke its ActionListener, or using the Enter key on a text field will do the same. However, there is no standard support for invoking an Action on a JList. I find this surprising, as most applications I’ve worked with support invoking an Action when either the Enter key is pressed or when the mouse is double clicked.
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Do you need the ability to create an image of your GUI or a component on your GUI? The easiest way to do this would be to use the Robot class and its createScreenCapture(…) method. This will work whether you have an AWT or Swing application. However, this method is relatively slow as it gets the pixels directly from the screen. There must be a better way.
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Many people want to know how to add a backgound image to a frame. The easiest way to do this is to add an image to a JLabel and then add the label to the frame. Is there a better way? Well, the answer depends on your requirements.

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JTable uses renderers to display data in each cell of the table. This allows for data to easily be displayed in different formats in any given cell.  However, the table only provides support for a few basic renderers:

• Boolean – rendered with a check box.
• Number – rendered by a right-aligned label .
• Date – rendered by a label.
• Icon – rendered by a centered label.
• Object – rendered by a label that displays the object’s string value.

Not much to choose from when you want to jazz up the display of your data. Fortunately we can easily create a renderer which will allow us to format the data in various ways.