> For the complete documentation index, see [llms.txt](https://codehs.gitbook.io/apjava/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://codehs.gitbook.io/apjava/basic-java/variables-and-types.md).

# Variables and Types

Variables allow us to store information such as numbers, words, or true/false expressions. A variable can be thought of as a box that stores information inside. In Java, variables are composed of three things: a name, type, and value.

## Primitive Types

In Java we must specify what ***type*** of information we want our variables to hold. You must always give your variable a type before naming it, and specifying the value it holds. (Ex. `int myVariable = 10;`)

Here are some of the primitive types found in Java:

![Primitive Types Table](https://3899603656-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4CE_DjWtTxVmIYccGI%2F-M4CEbFz20voXskDd956%2F-M4CF65nO4748AsoiIjF%2Fbasic_java_variables_and_types_primitive_types_table.png?generation=1586139041816707\&alt=media)

### Numeric Type:

As seen above, primitive numeric types in Java include both integers and doubles.

**Integers** are whole numbers, or counting numbers. (Ex. -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5)

In Java we declare an integer using `int` before the variable name. Here are a couple of examples:

```java
int itemsInStore = 10; 

int numberOfMessages = 8;
```

**doubles** are like integers, but can have decimals. (Ex. -54.34, 90.21, 0.1223)

In Java we declare a double using `double` before the variable name. Here are a couple of examples:

```java
double costOfApple = 1.24;

double milesToRun = 5.64;
```

### Char Type:

**Characters** represent a single character.

In Java we declare a character using `char` before the variable name. We also use single quotes to identify a character (Ex. `'A'`). Here are a couple of examples:

```java
char currentGrade = 'A';

char favoriteLetter = 'W';
```

### Boolean Type:

**Booleans** are variables that hold a true or a false value.

In Java we declare a boolean using `boolean` before the variable name. Here are a couple of examples:

```java
boolean passedCalculus = true;

boolean hasDog = false;
```

### String Type:

**Strings** are variables that hold text. Strings are **not** a primitive type, so you must declare them using `String` with a capital **S**. Unlike characters, we need to use double quotes when assigning strings (Ex. `"This is my string."`). Here are a couple of examples:

```java
String fishName = "Dog";

String myUniversity = "Arizona State University";
```

## Naming Variables

Giving your variables meaningful names throughout your code is very important. Proper variable names allow others to easily read and understand your code. A good way to name your variables is to give them as descriptive of a name as possible, without making it too long. For example, `int numberOfApplesOnTheTree = 10;` is a very long name, and can easily be replaced with a name like `int numApples = 10;`.

Variable Naming Conventions:

* Variable names must start with a letter, `$` symbol, or `_` symbol.
* Variable names are case sensitive so `myVariable` is different than `MyVariable`
* Variable names, after the first character, can contain letters, numbers, or other characters.

Here are some examples of different variable names:

![Variable Names Table](https://3899603656-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M4CE_DjWtTxVmIYccGI%2F-M4CEbFz20voXskDd956%2F-M4CF65p9vH7znSM5ZQ7%2Fbasic_java_variables_and_types_variable_names.png?generation=1586139041955919\&alt=media)