Some basic data types

The most important basic types you will need first are:

Int

An integer in the range \(-2^{31}\) to \(2^{31}-1\).

Long

Sometimes we want to use integers larger than the maximal number allowed by the Int type. In that case, we can use the type Long, which covers the range \(-2^{63}\) to \(2^{63}-1\). To create a Long object, write a number followed by L, like 123L. (If you need even larger integers, you can use the type java.math.BigInteger, which represents arbitrarily large integers. But BigInteger is much slower.)

Boolean

Either true or false (be careful: different from Python, in Kotlin these are written with small letters).

Double

A floating-point representation of a real number.

Char

A single character. To create a Char object, write a character enclosed in single quotation marks, like 'A'. Kotlin supports Unicode characters, so a Char object can also be a Hangul syllable.

String

A sequence of characters such as "Hello World". The next section has more information about strings.

For completeness, other basic types in Kotlin are Byte, Short, and Float. Don't use them unless you know what you are doing.

Converting between types

You can convert objects between the basic types by using their conversion methods:

>>> 98.toChar()
b
>>> 'c'.toDouble()
99.0
>>> 'c'.toString()
c
>>> 98.55.toInt()
98

Note that there is no automatic conversion between the number types, not even from Int to Long or from Int to Double. You have to use the conversion methods when you need to assign an integer to a Double:

>>> val a = 17
>>> val b: Double = a
error: type mismatch: inferred type is kotlin.Int but kotlin.Double was expected
>>> val b: Double = a.toDouble()

Operators

Kotlin's numerical operators are +, -, /, and %. Like in Python 2, Java, and C, the division operators / and % perform an integer division if both operands are integer objects. Note that there is no power operator in Kotlin (you can use the Math.pow library function to do exponentiation).

You can use the shortcuts +=, -=, etc.

You can compare numbers or strings using ==, !=, <, >, <=, and >=.

The boolean operators are ! for not, && for and, and || for or, as in C and Java. (These somewhat strange operators were invented for C in the early 1970s, and have somehow survived into modern programming languages.) Like in Python, Java, and C, these operators only evaluate their right hand operand when the result is not already known from the value of the left hand operand.

Sooner or later, you may meet the bitwise operators: and, or, xor, inv, shl, shr, and ushr. They work on the bit-representation of integers. Don't use these operators unless you know what you are doing.

The equality and inequality operators == and != can be used for objects of any type.

The mathematical constants and functions are methods of the object Math, the equivalent of the Python math module. For instance:

>>> val pi = Math.PI
>>> pi
3.141592653589793
>>> val t = Math.sin(pi/6)
>>> Math.sin(pi/4)
0.7071067811865475
>>> Math.sqrt(2.0)/2
0.7071067811865476