Question

State whether each of the following is true or false. If false, explain why. a) The first two arguments of Graphics method draw0val specify the center coordinate of the oval. b) In the Java coordinate system, \(x\) -values increase from left to right. c) Graphics method fillPolygon draws a filled polygon in the current color. d) Graphics method drawArc allows negative angles. e) Graphics method getSize returns the size of the current font in centimeters. f) Pixel coordinate (0,0) is located at the exact center of the monitor.

Short answer

a) False, b) True, c) True, d) True, e) False, f) False.

Step-by-step solution

Understanding the 'drawOval' Method

Statement: The first two arguments of Graphics method drawOval specify the center coordinate of the oval. - In Java, the `drawOval(int x, int y, int width, int height)` method does not use the center coordinates of the oval as the first two arguments. Instead, these arguments specify the starting point (upper-left corner) of the oval's bounding rectangle. - Therefore, this statement is False. The first two arguments specify the top-left corner, not the center.

Java Coordinate System Analysis

Statement: In the Java coordinate system, \(x\) -values increase from left to right.- In Java's coordinate system, points are laid out such that as you move to the right, \(x\) values increase.- This statement is True. The coordinate system behaves similarly to traditional Cartesian coordinates along the \(x\) axis.

Exploring 'fillPolygon' Method Functionality

Statement: Graphics method fillPolygon draws a filled polygon in the current color. - The `fillPolygon` method indeed draws a filled polygon based on the x, y coordinates of the vertices. It fills the shape using the current set drawing color. - Hence, this statement is True.

Draw Arc Functionality Examination

Statement: Graphics method drawArc allows negative angles. - The `drawArc` method can accept negative angles. A negative angle means drawing in a clockwise direction instead of counter-clockwise. - Therefore, this statement is True. Negative angles are permissible and affect the drawing direction.

Evaluating 'getSize' Method

Statement: Graphics method getSize returns the size of the current font in centimeters. - The `getSize` method of a Font object in Java returns the font size in points, not in centimeters. - Hence, this statement is False. It does not return size in centimeters.

Coordinate System Center Investigation

Statement: Pixel coordinate (0,0) is located at the exact center of the monitor. - In the Java coordinate system, the origin (0,0) is located at the top-left corner of the component or screen, not in the center. - Therefore, this statement is False. The origin (0,0) is at the top-left, not at the center.

Key concepts

Java coordinate system

In the Java coordinate system, you can imagine the screen as a graph from mathematics. However, it's a bit different than traditional Cartesian coordinates. Here, the origin point, (0,0), is located at the very top-left corner of the screen or window, not the center.
When you move across the screen from left to right, the x-values indeed increase, much like you would expect with positive x-values in graphing.
As you move downwards on the screen, the y-values increase. This may seem counterintuitive because, in typical mathematical graphs, y-values increase as you move up.

• The origin is at the top-left: (0,0)
• X-values increase from left to right
• Y-values increase top to bottom.

This system is essential for all graphic operations in Java, and understanding it can help you position your drawings accurately on the screen.

drawOval method

The `drawOval` method is part of Java's Graphics class, allowing you to draw ovals or circles on the screen. The method signature `drawOval(int x, int y, int width, int height)` provides a way to specify the dimensions and position of the oval by drawing the oval inside a bounding rectangle.
Contrary to what some may think, the `x` and `y` parameters don't set the oval's center. Instead, they indicate the upper-left corner of the rectangle that would bound the oval.
Here's how it works:

• `x` and `y` specify the top-left corner of the bounding rectangle
• `width` and `height` determine the size of the oval

If you want to draw a circle, simply ensure the `width` and `height` are equal, and Java will draw a perfect circle for you.

fillPolygon method

When it comes to drawing filled shapes in Java, the `fillPolygon` method comes in handy. It is part of the Graphics class and fills a polygon defined by a set of x and y coordinates.
You provide arrays of vertices (points) that determine the corners of your polygon. Consequently, the method will fill in the shape using the current drawing color specified by the graphics context.

• Define vertices with two arrays: `int xPoints[]` and `int yPoints[]`
• `int nPoints` specifies the number of points (vertices)
• The polygon is automatically filled with the current color

Notably, these filled polygons offer a way to create complex shapes with color, enhancing the visual output of Java apps.

drawArc method

The `drawArc` method is a flexible function in Java's Graphics class, used to draw an arc defined by a section of an oval. Often used for more dynamic or partially-rounded shapes, the `drawArc` method has interesting capabilities.
One of the key features of `drawArc` is the ability to accept negative angles. Negative angles allow for arcs to be drawn in a clockwise direction, as opposed to the counter-clockwise, which is the default.

• Angles are measured in degrees
• A negative angle draws clockwise
• Use a positive angle for counter-clockwise drawing

Knowing how to leverage angles enables creating complex designs efficiently and according to your graphic needs.

Java Font size measurement

When dealing with text in Java, it's important to understand how font sizes are measured. Java uses a unit called "points" to measure font size, which is a common typographic measure.
The method `getSize()` from a Font object returns the font size in these points, not in centimeters or any other unit.
Understanding how many points translate into physical sizes depends on your display or printer settings, as one point generally equals 1/72 of an inch.

• Points measure the size of the font (1 point is 1/72 of an inch)
• `getSize()` method provides the size in points

Understanding this is crucial for developers who need precise control over text appearance in their Java applications.