Java Reference
In-Depth Information
9.6 Important Points
1. In order to create a window in Java, create a class that inherits from the JFrame class
and instantiate it.
2. Call the setVisible method on a window in order to make it visible.
3. Initialize the content of the window inside the constructor of the class that inherits
from the JFrame class.
4. The paintComponent method does the drawing inside a JPanel . It will be called mul-
tiple times (i.e., every time the window needs to be repainted). The paintComponent
method takes as input an object of type Graphics , which is used to do the drawing.
Always call the super class at the beginning of the paintComponent method, which
guarantees that you will start painting on a blank canvas.
5. The paintComponent method only displays the data. It should never generate new
6. Never call the paintComponent method directly. Instead, call the repaint method in
order to refresh a panel.
9.7 Exercises
1. Write code that displays the picture from Figure 9.4, that is, a circle and a horizontal
and vertical line segment through its center.
2. Write code that displays the window from Figure 9.5. The ball is displayed as an
image (search the Internet for a blue ball to get a similar image). Set the initial size
of the window appropriately and make the window non-resizable.
3. Write a program that displays GAME OVER in the middle of a window. The text color
should be white, while the background color should be red.
FIGURE 9.4: Picture for Exercise 1.
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