Question

Class Graphics contains method drawOval, which takes as arguments the same four arguments as method drawRect. The arguments for method drawOval specify the “bounding box” for the oval—the sides of the bounding box are the boundaries of the oval. Write a Java applet that draws an oval and a rectangle with the same four arguments. The oval will touch the rectangle at the center of each side.

Short answer

The solution involves creating a Java applet, overriding the paint method to draw a rectangle and an oval with identical bounding box parameters, which results in the oval touching the rectangle at the center of each side.

Step-by-step solution

Import necessary packages

Begin by importing the necessary Java packages for applet creation and graphics drawing. This will include 'java.applet.Applet' for the applet and 'java.awt.Graphics' for drawing shapes.

Define the applet

Define a public class that extends the 'java.applet.Applet' class. This class will be the applet that contains the drawing methods.

Override the paint method

Override the 'paint' method of the applet. This method is called when the applet is first drawn and whenever it is refreshed. Inside this method, we will call 'drawRect' and 'drawOval'.

Set the bounding box parameters

Define four integer parameters that represent the bounding box: 'x', 'y', 'width', and 'height'. These determine where the shapes will be drawn and their sizes.

Draw the rectangle

Use the 'drawRect' method of the 'Graphics' class to draw the rectangle. Pass the bounding box parameters to this method to set its position and size.

Draw the oval

Use the 'drawOval' method of the 'Graphics' class to draw the oval. Pass the same bounding box parameters to this method as well. Given the same parameters, the oval will touch the rectangle at the center of each side.

Compile and run the applet

Compile the Java applet and run it using an applet viewer or a web browser that supports Java to see the oval and rectangle drawn with the same bounding box parameters.

Key concepts

Graphics class

In the world of Java programming, the Graphics class is a pivotal element whenever we deal with drawing graphics on components. It serves as an abstract base class that provides the basic functionalities to draw texts, lines, shapes, and images onto the Java components that are typically displayed within a window or an applet.

The Graphics class is part of the java.awt package, which stands for Abstract Window Toolkit. This package provides classes for creating and managing graphical user interface (GUI) components such as buttons, text fields, and frames. It is truly a cornerstone for any Java developer looking to add visual elements to their applications.

Using the Graphics class typically begins by overriding the paint() method of a component, which is automatically called when the component needs to be rendered. Within this method, we invoke various drawing methods provided by the Graphics class to actually draw shapes and images on the screen.

drawOval method

When you want to draw an oval in Java, the drawOval method of the Graphics class is your go-to tool. This crucial method takes four parameters—(int x, int y, int width, int height), which describe the oval's 'bounding box'.

The parameters x and y specify the upper-left corner of the bounding box that encloses the oval. The parameters width and height dictate the size of this box, and hence, the size of the oval itself.

An important thing to remember is that the drawn oval will be inscribed within this bounding box. This means that the edges of the oval will touch the midpoints of each side of the rectangle, assuming the rectangle is defined by the same set of bounding box parameters.

drawRect method

Complementary to the drawOval method is the drawRect method, another essential feature of the Graphics class. This method is used to draw rectangles and is invoked with the same set of four parameters—(int x, int y, int width, int height).

Just like with drawOval, x and y define the location of the upper-left corner of the rectangle. The width and height parameters determine the dimensions of this rectangle.

The convenience of these consistent parameter requirements between drawRect and drawOval allows you to overlay one shape over the other seamlessly, making it simple to combine shapes in various creative ways within your Java applet.

Bounding box parameters

Bounding box parameters are essential when we want to draw shapes that require precise placement and sizing. These parameters—x, y, width, and height—define a rectangular area within which our shapes will fit. Essentially, they draw an invisible box that serves as a reference to render an oval or a rectangle.

The parameters have a specific interpretation:

• x and y are the coordinates of the upper-left corner of the bounding box.
• width and height represent the size of the bounding box along the x-axis and y-axis, respectively.

Understanding these parameters is crucial, especially when you want the shapes to adhere to a certain alignment or proportion. Any graphical object that our Graphics class methods draw will be constrained to fit within this bounding box, ensuring a level of control and predictability in our graphical output.