This book is now obsolete Please use CSAwesome instead.
3.1. What is a Variable?¶
The following video is also on YouTube at https://youtu.be/pHgYlVjagmA. It explains what a variable is and gives a couple of real word examples of variables.
A variable is a name associated with a memory location in the computer. Computer memory can store a value and that value can change or vary. When you play a game, it will often have a score. Scores often start at 0 and increase. A score is a variable.
3.1.1. Variable Types on the Exam¶
There are two types of variables in Java: primitive variables that hold primitive types and object variables that hold a reference to an object of a class. A reference is a way to find the object (like a UPS tracking number helps you find your package). The primitive types on the Advanced Placement Computer Science A exam are:
int - which store integers (whole numbers like 3, -76, 20393)
double - which store floating point numbers (decimal numbers like 6.3 -0.9, and 60293.93032)
boolean - which store Boolean values (either true or false).
String is one of the object types on the exam and is the name of a class in Java. A string object has a sequence of characters enclosed in a pair of double quotes - like “Hello”. You will learn more about
String objects in another chapter.
Some languages use 0 to represent false and 1 to represent true, but Java uses the keywords
Check your understanding