1. Introduction
2. Class 101
3. Java API
4. Writing a Class
5. Constructing Instances
6. Writing the Code
7. Javadoc
8. Generating HTML
9. Checkpoint 1
10. The Rabbit Problem
11. The Rabbit Simulator
12. Checkpoint 2

Class 101

Java has 8 primitive types such as int, double, and boolean for numbers and simple true/false values. Everything else is some kind of object. The definition for an object type is called a class.

Java provides a number of predefined classes: we have used System to access the standard output stream and we have also seen the String class for text. As with the primitive data types, you must declare a variable of a class in order to use it:

String message;

Also, just as with primitives, you must initialize the variable. A variable whose type is a class can store a reference to an object which is an instance of that class. In the case of String, it is easy to construct a new instance: we can just put some text in quotes:

message = "Hello, world!";
System.out.println(message);

Invoking methods

Most classes also define operations, called methods, that allow you to examine or modify the data in each instance. You can invoke or call a method using the dot operator on an instance of the class.

For example, the class String has many methods available. A commonly used method is length, which retrieves the length of a string.

int theLength = message.length();
System.out.println(theLength);

In your lab2 package, write a class named StringTest with a main method to try this out. Consult the previous lab if you do not remember to how create a class and main method. Run it and inspect the output.