Beginning Java/Variables

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Variables are devices that store data in memory (much like short our short term memory), they are an essential feature that all programming languages share.

Primitive vs Reference[edit]

There are two main types of variables.

  • Primitive - this data is stored directly in memory, every primitive data type is a number of varying ranges. There are eight primitive data types in Java: byte, short, int, long, float, double, boolean, and char.
  • Reference - also known as objects, a reference does not contain the actual data, rather it contains a "pointer" to where the data is held. The examples are Object, Vector, and String.

Declaration[edit]

To use a variable we must first declare it. In Java we do use the following structure (formally known as syntax):

<variable type> <variable name>;

You will learn about types later in this chapter.

It's name can be anything as long as it's made up of only letters, numbers, "_" and "$". Variables are case sensitive (so "message" is different from "Message").

The following demonstrates an example of variable declaration
String message;
This will create a new String variable called "message"


Types[edit]

Java is what's known as a "strongly typed" language, which means each variable explicitly a certain type (e.g. number, string etc).

Integers[edit]

These represent whole numbers (1, 2, 3...). The "int" type is the most commonly used integer, and has a range of about ± 2.1 billion.

Strings[edit]

As seen before, strings store textual data.

Boolean[edit]

Floats and Doubles[edit]

Exercise[edit]