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In Swing JPanel said to be opaque, what does that mean?
Also how JPanel VS JComponent compared in relation to opaque?
Please explain if possible in simple terms, hence i am not very experienced in GUI programming.
Thanks in advance for your help
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The term opaque has different meanings in Java 2D and in Swing. In Java 2D opacity is a rendering concept. It is a combination of an alpha value and the Composite mode. It is a degree to which the pixel colours being drawn should be blended with pixel values already present.
JPanel, a part of the Java Swing package, is a container that can store a group of components. The main task of JPanel is to organize components, various layouts can be set in JPanel which provide better organization of components, however, it does not have a title bar.
JPanel class works as a container to host components. JFrame is generally used as a window for hosting stand-alone applications, like an alert window or notification window. JFrame has different inner frames for performing different purposes. In the case of JPanel, one pane can hold multiple operations.
Opaque has a very specific meaning in Swing - it means that the component fully paints the full area within its bounds (see the setOpaque javadoc)
This is used primarily to determine whether it is necessary to repaint components behind the current component.
If you are creating your own JComponent and setOpaque to true but do not honour the contract (i.e. you do not draw the full area within the bounds despite claiming to be opaque) then you may get unexpected results due to the background not being redrawn.
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