Question

Class Graphics contains method draw0val, which takes as arguments the same four arguments as method drawRect. The arguments for method draw0val 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

Create an applet with a paint method that uses drawRect and drawOval with the same parameters for alignment.

Step-by-step solution

Understand the Applet Class

In Java, an applet is a small application designed to be executed by an AppletViewer or a web browser. To create an applet, your class must extend the Applet class and override its paint method, where the drawing will be done.

Recognize the Graphics Method Requirements

Both `drawOval` and `drawRect` methods require four parameters: `x`, `y`, `width`, and `height`. These define the bounding box for the shapes. The `x` and `y` parameters specify the starting point of the bounding box at the top-left corner, while `width` and `height` specify the dimension of the box.

Set Up Bounding Box Parameters

Decide on the values for `x`, `y`, `width`, `height` that both the oval and rectangle will use. For this case, set `x = 50`, `y = 50`, `width = 200`, and `height = 100`. This will locate the shapes centrally in the applet view.

Override the Paint Method

Override the `paint(Graphics g)` method in your applet class. This method is used for drawing the shapes. Within this method, use `g.drawRect(x, y, width, height)` and `g.drawOval(x, y, width, height)` to draw the rectangle and the oval.

Implement the Applet

Here's how you can implement the applet: ```java import java.applet.Applet; import java.awt.Graphics; public class MyShapeApplet extends Applet { public void paint(Graphics g) { int x = 50; int y = 50; int width = 200; int height = 100; g.drawRect(x, y, width, height); g.drawOval(x, y, width, height); } } ```

Verify the Drawing in AppletViewer

After implementing the Java applet, compile and run it using an AppletViewer or a web browser that supports applets. Check that the rectangle and oval are drawn such that the oval touches the center of each side of the rectangle, demonstrating correct alignment of both shapes.

Key concepts

Graphics class

In the realm of Java programming, the `Graphics` class is an essential part of the Abstract Window Toolkit (AWT) package. It provides the necessary tools to draw shapes, text, and images on the Java window or applet. When you're working with Java applets or any graphical program, you often need to paint components — this is where the `Graphics` class shines.

Think of `Graphics` as a canvas and the program's paint method as the brush. With this canvas, you can create numerous graphical elements, such as lines, rectangles, circles, arcs, and more. The `Graphics` class provides a simple way to control the color, style, and layout of these elements.

When drawing with the `Graphics` class, you need to override the `paint` method. This method receives a `Graphics` object, which is your gateway to any graphical element you want to display. Remember, `Graphics` is not just about drawing. It's a fundamental part of customizing any Java component visually.

drawOval and drawRect methods

The `drawOval` and `drawRect` methods in Java's `Graphics` class offer a straightforward way to draw ovals and rectangles, but with a nifty feature: they share the same set of arguments. This design makes it easy to position these shapes in relation to each other.

Both methods require four parameters:

• `x` and `y`: These parameters determine the coordinates of the upper-left corner of the shape's bounding box. They are your starting point for where the shape will be placed.
• `width`: This parameter defines how wide the oval or rectangle will be. For an oval, this is the width of the bounding box that contains the whole oval.
• `height`: This indicates the height of the shape’s bounding box.

Using these parameters allows you to precisely position and size your oval and rectangle so that they align perfectly. For instance, by using the same x, y, width, and height for both methods, you get an oval that fits snugly inside a rectangle, touching each side exactly at its center. This is a crucial concept when working on graphical user interfaces or any graphics-based applications.

bounding box

The idea of a "bounding box" is central in graphics programming and plays a key role in methods like `drawOval` and `drawRect`. Essentially, a bounding box is a rectangular region that completely encompasses a shape, like an oval.

When using `drawOval`, think of the oval as a shape drawn within an imaginary rectangle. This rectangle is bounded by the parameters you provide: `x`, `y`, `width`, and `height`. The term "bounding" indicates that this box limits the maximum width and height of the shape drawn inside it.

For a rectangle, the concept is more straightforward, as the bounding box itself is the shape drawn. However, with an oval, the rectangle acts as the shape's container, defining the oval's horizontal and vertical extremities.

This bounding box concept is crucial for aligning different shapes. When an oval is said to "touch" a rectangle at the center of each side, it means that their bounding boxes are perfectly aligned, using the same dimensions and position. Thus, mastering bounding boxes is vital to control spatial relationships in graphics.

paint method

The `paint` method is an integral element of Java's graphical component system. It plays a vital role in how graphics are drawn to the screen. Whenever you want to draw something, you do it inside the `paint` method.

When creating a Java applet or application, the `paint` method is where you define how the component will visually render. This includes drawing shapes, text, or images using the `Graphics` object passed to it as an argument.

The `paint` method is automatically invoked by the Java runtime whenever a component needs to be rendered or refreshed. This occurs, for example, when the window becomes visible for the first time or when it needs to be updated after being covered. Inside the `paint` method, you can call various drawing methods like `drawRect` and `drawOval`. Each call uses the `Graphics` object to direct how and where to draw the shapes.

Remember to override the `paint` method in your custom applet or component classes, and avoid directly invoking it. Instead, use `repaint()`, which indirectly calls `paint()`, ensuring the component updates properly. This method is the backbone of visual customization in Java applications.