GroovyCookBook: Numbers

GroovyCookBook: Numbers

Numbers

Introduction

Groovy makes heavy use of Java's numeric capabilities. This means that Groovy supports both the primitive and object number types available in Java but with a few enhancements thrown in.

The main highlights are that Groovy provides a more consistent view of numeric types to the developer. This is achieved through two main mechanisms:

• Dealing with primitives is made to look like dealing with objects. E.g. you can go "42.toString()". In fact, primitives are autoboxed to their wrapper equivalents most of the time. Where needed for Java integration purposes, primitive types are retained.
• Dealing with BigIntegers and BigDecimals (as well as your own types and 3rd part library types like Matrix or Complex number) is made to be the same as dealing with the simpler types, e.g. if I have three BigInteger or three Matrix instances called a, b and c, then I can write an expression like def d = (a + b) * c. This is achieved through operator overloading.

These features align with some of the Groovy language's guiding philosophies, namely "everything is an object" and "improved consistency where possible".

Primitive numeric types

The following primitive types are supported:

Name	Description	Allowed values	Example
byte	8-bit signed two's complement	-128 to 127	42
short	16-bit signed two's complement	-32,768 to 32,767	20000
int	32-bit signed two's complement	-2,147,483,648 to 2,147,483,647	1000000000
long	64-bit signed two's complement	-9,223,372,036,854,775,808 to +9,223,372,036,854,775,807	1000000000000000000
float	32-bit IEEE 754 floating-point value	1.40129846432481707e-45 to 3.40282346638528860e+38	3.5f
double	64-bit IEEE 754 floating-point value	4.94065645841246544e-324d to 1.79769313486231570e+308d	3.5d

Primitives are nearly always converted ("boxed") to their wrapper types. Autoboxing and unboxing happens automatically behind the scenes if integrating with Java APIs.

Class numeric types

In addition to the primitive types, the following object types (sometimes referred to as wrapper types) are allowed:

Name

java.lang.Byte

java.lang.Short

java.lang.Integer

java.lang.Long

java.lang.Float

java.lang.Double

As well as the following classes for supporting arbitrary precision arithmetic:

Name	Description	Example
java.math.BigInteger	Immutable arbitrary-precision signed integral numbers	30g
java.math.BigDecimal	Immutable arbitrary-precision signed decimal numbers	3.5g

Java automatically imports all classes from the java.lang package. Groovy also does this for the BigInteger and BigDecimal classes, so you don't need to import any of these classes.

Declaring numeric variables

You can declare variables using either the primitive or wrapper variants (and optionally provide an initializing literal):

byte b1 = 42
Byte b2 = 42
short s1 = 20000
Short s2 = 20000
int i1 = 1000000000
Integer i2 = 1000000000
long l1 = 1000000000000000000
Long l2 = 1000000000000000000
Long l3 = 42L
float f1 = 3.5f
Float f2 = 3.5f
double d1 = 3.5e40
Double d2 = 3.5e40
Double d3 = 3.5d
BigInteger bi = 30g
BigDecimal bd = 3.5g
[b1, b2, s1, s2, i1, i2, l1, l2, l3, f1, f2, d1, d2, d3, bi, bd].each{ println it.dump() }

which produces this output:

<java.lang.Byte@2a value=42>
<java.lang.Byte@2a value=42>
<java.lang.Short@4e20 value=20000>
<java.lang.Short@4e20 value=20000>
<java.lang.Integer@3b9aca00 value=1000000000>
<java.lang.Integer@3b9aca00 value=1000000000>
<java.lang.Long@aa84b6b3 value=1000000000000000000>
<java.lang.Long@aa84b6b3 value=1000000000000000000>
<java.lang.Long@2a value=42>
<java.lang.Float@40600000 value=3.5>
<java.lang.Float@40600000 value=3.5>
<java.lang.Double@fbd347d4 value=3.5E40>
<java.lang.Double@fbd347d4 value=3.5E40>
<java.lang.Double@400c0000 value=3.5>
<java.math.BigInteger@1e signum=1 mag=[30] bitCount=-1 bitLength=-1 lowestSetBit=-2 firstNonzeroByteNum=-2 firstNonzeroIntNum=-2>
<java.math.BigDecimal@43e intVal=null scale=1 precision=2 stringCache=null intCompact=35>

Converting between strings and numbers

For simple cases, converting from a string to a number is relatively straight forward. This code illustrates some options for integers (the same variants apply for other numeric types):

def string = "300"
// check if it appears to be a number
println string.isNumber()

// ok, now convert to number in different ways
def i3 = string.toInteger()
def i4 = string as int
def i5 = string as Integer
def i6 = new Integer(string)
def i7 = Integer.parseInt(string)
[i3, i4, i5, i6, i7].each{ println it.dump() }

which produces this output:

true
<java.lang.Integer@12c value=300>
<java.lang.Integer@12c value=300>
<java.lang.Integer@12c value=300>
<java.lang.Integer@12c value=300>
<java.lang.Integer@12c value=300>

You can also check the validity of strings as a number using regular expressions, e.g.:

integerPattern = /^[+-]?\d+$/
assert '-36' =~ integerPattern
assert !('abc' =~ integerPattern)
decimalPattern = /^-?(?:\d+(?:\.\d*)?|\.\d+)$/
assert '37.5' =~ decimalPattern

Converting from numbers to strings

In most scenarios using toString() is the appropriate way to convert a number to a string. This only works with object types not primitives but in most cases, this is what Groovy converts your numbers to automatically for you.

println 2.dump()
def two = 2.toString()
println two
println two.dump()