Numbers and Math

Groovy's number handling has one big surprise for Java developers: decimal literals are exact.

println 0.1 + 0.2
println 0.1 + 0.2 == 0.3
println 0.1d + 0.2d

0.3
true
0.30000000000000004

0.1 is a BigDecimal, so money and measurements add up the way you expect. Add a d suffix (or declare a double) when you want fast, approximate floating-point math.

Arithmetic

println 7 + 2
println 7 - 2
println 7 * 2
println 7 / 2           // division gives a decimal
println 7.intdiv(2)     // whole-number division
println 7 % 2           // remainder
println 2 ** 10         // power
println(-7.abs())       // parentheses: minus applies after the call

9
5
14
3.5
3
1
1024
-7

• / between two integers gives a BigDecimal, not a truncated integer as in Java. Use intdiv() for whole-number division.
• ** raises to a power.
• Careful with a leading minus: -7.abs() means -(7.abs()).

Number literals

println 1_000_000
println 0xFF
println 0b1010
println 42L.getClass().simpleName
println 42G.getClass().simpleName
println 1.5f.getClass().simpleName
println 2 ** 100

1000000
255
10
Long
BigInteger
Float
1267650600228229401496703205376

Underscores group digits. Suffixes pick a type: L long, G BigInteger (or BigDecimal for decimals), f float, d double. Integer powers that overflow become BigInteger automatically.

Rounding and Math

def price = 19.999
println price.setScale(2, java.math.RoundingMode.HALF_UP)
println Math.round(2.5)
println Math.sqrt(16)
println Math.max(3, 9)
println 10.5.toInteger()
printf('%.2f%n', 3.14159)

20.00
3
4.0
9
10
3.14

Math is Java's java.lang.Math, available without an import. setScale rounds a BigDecimal to a number of decimal places.

Common mistakes

• Expecting 7 / 2 to be 3 — it's 3.5. Use intdiv.
• int arithmetic can still overflow: Integer.MAX_VALUE + 1 wraps to a negative number, exactly as in Java. Use long or BigInteger for very large values.

Practice

A pizza costs 12.40 and is shared by 3 people. Print each person's share rounded to 2 decimal places, and how many whole pizzas 50 can buy.

def share = 12.40 / 3
println share.setScale(2, java.math.RoundingMode.HALF_UP)
println((50 / 12.40).toInteger())

4.13
4