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- Oct 02, 2019 JPanel is a Swing’s lightweight container which is used to group a set of components together. JPanel is a pretty simple component which, normally, does not have a GUI (except when it is being set an opaque background or has a visual border). In this article, we summarize the common practices when working with JPanel in Swing. At the end, we will create a sample program looks like this.
- $begingroup$ Key listeners are good for handling keyboard events on components. Instead if you are making a game and are generally interested in the keyboard events unrelated to any components, I have found this approach to work better. $endgroup$ – msell Nov 23 '12 at 14:25.
- 4 JFrame: Displaying Labels with Icons
- 7 Selection Lists
- 8 Mouse Event Handling
- 10 Layout Managers
Introduction
JOptionPane: displaying a message in a panel
Swing Components and AWT
JFrame: Displaying Labels with Icons
Introduction to Event Handling with TextFields
// set input text to upper case
tempString = tempString.toUpperCase();
((JTextField)event.getSource()).setText( tempString);
- Create a class (e.g. TextFieldHandler) that represents the event handler. This could be an inner class.
- Implement the appropriate event-listener interface (e.g. ActionListener) in the class just created (e.g. TextFieldHandler).
- Register the event handler with the object that may generate the event. To do this you will need to create an instance of the above class (e.g. TextFieldHandler) and use the appropriate method (e.g. addActionListener) to do the registering.
Event Listeners
Buttons
Jpanel Doesn't Generate Key Event List
Jpanel Doesn't Generate Key Event Calendar
JComboBox: Pull-down list selection, using an anonymous inner class
A combo box (aka a drop-down list) provides a list of items from which the user can choose. See the ComboBoxFrame class (and driver) for a demonstration.
Rather than having a separate driver, this example is all in one file. Pay careful attention to how main() sets the event listener for the application window. The code given there is:
object.addItemListener( handler);
- Compiling a class that contains an inner class results in a separate .class file for every class. Inner classes with names have the file name OuterClassName$InnerClassName.class. Anonymous inner classes have the file nameOuterClassName$#.class where # starts at 1 and is incremented for each anonymous inner class encountered during compilation. A file list from the compilation of the above example is shown below to illustrate this.
- Inner classes with class names can specify access specifiers public, private, or protected.
- To access an outer class's this reference, use OuterClassName.this
- Though perhaps not recommended, it is possible to create an object of another class's inner class, assuming it is public. To do this first create an object of the outer class and assign it a reference (we'll call it ref). Then use a statement of the following form:
OuterClassName.InnerClassName innerRef = ref.new InnerClassName();
An inner class can be declared static.
Selection Lists
JList
See an example in the ListFrame class (and driver). Running the program allows you to select a color from a selection list, where the background is then set to that color:
Multiple Selection Lists
See an example in the MultipleSelectionFrame class (and driver). Running the program allows you to choose multiple options from the left-hand list using single or multiple selection. The selected color names are then copied over to the right-hand list:
Mouse Event Handling
Tracking
In the code note that the BorderLayout is the default layout manager for a JFrame. It is necessary to define all 7 of the methods from both interfaces that are implemented (MouseListener and MouseMotionListener). To avoid having to do this use an Adapter Class (see the API tutorial list of Adapters), as illustrated in the example below.