• Tips For Golfing In Groovy

Parsing

Converting strings to integers

x.toInteger()
x as Integer
x as int

Looping through list/string

for(a:args){a} // Java-style syntax; braces may be omitted if the body is only one statement
args.any{it} // Must return falsy value to keep iterating
args.min{it} // Sometimes useful for non-falsy values
args.each{it} // Most general iteration method, but rarely optimal

Looping through integers

10.times{}
for(n:0..9){} // better than .times when the variable is used at least twice and braces aren't needed
0.upto(10){}
(0..9).any{} // or any other list methods
0.step(10,2){} // loop with a step

Type Annotations

Type annotations are optional in Groovy and should usually be avoided. However they can sometimes actually make code shorter.

If you're storing an object in a variable anyway, the shortest way to invoke a class's constructor is:

ClassName v=[arg]
// vs
v=new ClassName(arg)

Typed variables can coerce values on assignment:

// Loop over the char values of the string
// Prints: 97 98 99 100
for(int c:'abcd')print"$c "

int i
// Typed variables are zero-initialized
// Prints: 0
println i

// We can do integer division without intdiv!
i=3/2
// Prints: 1
println i
i=5/2
// Prints: 2
println i
// However this still prints 2.5:
println(i=5/2)

Finally, if your solution is timing out, applying annotations to some of the variables can help Groovy optimize your code so it runs faster.

Misc

• Eval - Eval.me(), or evaluate() to have access to current scope (Warning: slow)
• Short-circuiting is allowed: i%2||println(i)
• Regex matching: x.matches("...") -> x=~/.../
• Sometimes you can save a byte by converting a string to regex and avoiding parentheses: println~(a+b).replace(...) vs println((a+b).replace(...)).
• In some situations, single-character strings can be treated like integers to save 1 byte. For example, 'a'==97 evaluates to true.
• Use spread-dot instead of collect to apply a method call to all elements in a collection: x*.multiply(2)
• Reference DefaultGroovyMethods and StringGroovyMethods for extra methods Groovy adds to common JDK classes. EncodingGroovyMethods is also worth a look.
• Become familiar with the Groovy operators and how they're overloaded for various types. Some are very useful.

Packers

2:1

evaluate new String('...'.getBytes('UTF-16LE'))

# python
print('CODE'.encode().decode('utf-16le'))