Think Java

Chapter 10. Objects

As we learned in the previous chapter, an object is a collection of data that provides a set of methods. For example, a String is a collection of characters that provides methods like charAt and substring.

Java is an “object-oriented” language, which means that it uses objects to represent data and provide methods related to them. This way of organizing programs is a powerful design concept, and we will introduce it a little at a time throughout the remainder of the book.

In this chapter, we introduce two new types of objects: Point and Rectangle. We show how to write methods that take objects as parameters and produce objects as return values. We also take a look at the source code for the Java library.

Point Objects

The java.awt package provides a class named Point intended to represent the coordinates of a location in a Cartesian plane. In mathematical notation, points are often written in parentheses with a comma separating the coordinates. For example, indicates the origin, and indicates the point x units to the right and y units up from the origin.

In order to use the Point class, you have to import it:

import java.awt.Point;

Then, to create a new point, you have to use the new operator:

Point blank;
blank = new Point(3, 4);

The first line declares that blank ...