Clojure's data types

String

String

"This is a string"

"This is a multiline string"

A string of characters; in Clojure you can use multiline strings without a problem

Boolean

Boolean

true

false

Literal Boolean values

Character

Character

\c

\u0045 ;; Unicode char 45 E

Character values, they are java.lang.Character instances, you can define Unicode characters

Keywords

Doesn't exist in java

:key

:sample

:some-keyword

They evaluate themselves and they are often used as keys. They are also functions that look for themselves in a map.

Number

Numbers are automatically handled as BigDecimal, BigInteger or lower precision depending on what's necessary

42N ;;Big Integer

42 ;;long

0.1M ;;BigDecimal

It is important to remember the trade-offs of Java numbers, if precision is important, you should always use big decimals and bigintegers.

Ratio

Doesn't exist

22/7

Clojure provides great numerical precision; if necessary it can retain the ration and execute exact operation. The tradeoff when using ratios is speed.

Symbol

Doesn't exist

some-name

Symbols are identifiers in Clojure, very similar to a variable name in Java.

nil

null

nil

The null value

Regular expressions

java.util.regex.Pattern

#"\d"

Regular expressions, in Clojure you get free syntax to define regular expressions, but in the end it is a plain old Java reggae Pattern

List

List

(1 2 3 4 5)

A simple list, notice the quote character before the list, if you don't specify it Clojure will try to evaluate the form as an instruction

Vector

Array

[1 2 3 4 5]

It is the main workhorse in Clojure, it is similar to an array because you can access elements in a random order

Set

HashSet

#{1 2 3 4}

A normal Java hash set

Map

HashMap

{:key 5 :key-2 "red"}

A Clojure map