It is quite an uncomplicated component which usually does not possess a graphical user interface GUI. However, it may have a GUI if it is laid out in an opaque background or contains a display border. The JPanel container class is found in the javax. The former enhances the serviceability of the latter. The JPanel is a very simple and lightweight container which is a subclass of the java. JComponent class. The JComponent in turn is a subclass of the container.
Consequently, several methods used for the JPanel are derived from its superclasses. Some of the examples of such methods include image observer, alignments and accessibility. The JPanel enables one to place checkboxes, buttons, images, fields, labels and even texts into it.
It s mainly defined as an area where controls and visuals can be placed in. To use a JPanel, one needs to first create its object which is done by calling for a constructor JPanel. Following this invocation, a blank panel is generated. Parts of drawings may go beyond the screen. This is not an error: such parts just won't be seen.
Here are prototypes for the simplest drawing methods in the Graphics class. Likewise, there are simlar methods that draw filled-in shapes. Note that we can call the getBackground method of a Component ; by drawing something in this color using the setColor method , Java will seem to erase what it underneath it. Examine the folder named figures jpanel in the View Demonstrations download.
It shows a short program small DrawPanel class, tiny View and Application class that illustrates how to use javax. JPanel for drawing figures in a JFrame. In this section we will examine two simple methods for drawing images in a graphics context. We have already seen how to read images stored in files with a Toolkit. We will now see how to render such images directly and how to render them after scaling them. Here are prototypes for the simplest image methods in the Graphics class.
The first method renders the image in it actual size; the second shrinks or expands it to the dimensions width and height. For now, we will specify null for the ImageObserver Examine the folder named images jpanel in the View Demonstrations download.
JPanel for drawing images. It draws a bunch of hot dogs, and moves them a bit each time enter is pressed in the console window. In this section we will examine some simple methods for drawing text in a graphics context. The process is straightforward, but it can involve two other interesting classes, Font and FontMetrics. Objects in the Font class are constructed, specified by a font name e.
Objects in the FontMetrics class describe a font, with lots of interesting information: the height and width of characters in the font, ascent and descent, etc. Here are prototypes for the simplest text methods in the Graphics class. The first method renders the text using the current font and color starting at the specified coordinate.
Before this statement we might write the following code to specify the font to use and get its metrics. JPanel for drawing text. It also illustrates some uses of the Font and FontMetrics classes, which are both defined in the java. Finally, in this section we will examine how to put buttons in JPanel s. Here we use Buttons only for their visual effect; in the lecture on Controllers we will learn how to make pressed buttons call appropriate methods in the Model.
Standard buttons are constructed from the JButton class in the javax. As with other controls, they inherit hundreds of methods. The typical constructor specifies a String to use as a label for the button or we can call setLabel with any String later. We can also call inherited methods such as setFont , setBackground , and setForeground , although most standard buttons use default values for these.
We can also call the setEnabled method with a boolean parameter to tell Java whether a button is pressable if not, its label will appear as a faded color. Here is an example of declaring a JButton and performing many of these operations. If you noticed from our above example, we use a Layout Manager to determine the location of each component.
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