Java Swing, 2nd Edition

A Simple Container

Not everything in this chapter is more complex than its AWT counterpart. As proof of this claim, we’ll start the chapter with a look at the JPanel class, a very simple Swing container.

The JPanel Class

JPanel is an extension of JComponent (which, remember, extends java.awt.Container) used for grouping together other components. It gets most of its implementation from its superclasses. Typically, using JPanel amounts to instantiating it, setting a layout manager (this can be set in the constructor and defaults to a FlowLayout), and adding components to it using the add( ) methods inherited from Container.

Properties

JPanel does not define any new properties. Table 8-1 shows the default values that differ from those provided by JComponent.

Table 8-1. JPanel properties

Property	Data type	get	is	set	Default value
accessibleContext o	AccessibleContext	·			JPanel.AccessibleJPanel( )
doubleBufferedo	boolean		·	·	true
layouto	LayoutManager	·		·	FlowLayout( )
opaqueo, b	boolean	·	·		true
UI1.4	PaneUI	·		·	From L&F
UIClassID	String	·			“PanelUI”
1.4since 1.4, bbound, ooverridden See also properties from the JComponent class (Table 3-6).

The doubleBuffered and opaque properties default to true, while the layoutManager defaults to a new FlowLayout.

Constructors

public JPanel( )

Create a new panel with a FlowLayout and double buffering.

public JPanel(boolean isDoubleBuffered)

Create a new panel with a FlowLayout. Double buffering is enabled if isDoubleBuffered is true.

public JPanel(LayoutManager layout) ...