Master programming syntax, solve interactive challenges & run live code in Syntaxis Explore Arena →
menu_book Course Curriculum (Groovy) expand_more
Syntax and Values
Def dynamic variables Typed variables GString interpolation Triple-quoted strings List literals Map literals Range literals Safe navigation operator Elvis operator Spread operator
Control Flow
If else expressions Switch expressions For in loops While loops Truthiness rules Ternary operator Multiple assignment Regex match operator Regex find operator Assertions
Closures
Closure literals Implicit it parameter Explicit closure parameters Closure return values Closure delegation Owner thisObject delegate Currying closures Memoized closures Composition with rightShift Trampoline recursion
Collections
Each iteration Collect mapping Find and findAll Inject reduction GroupBy Sort with closure Unique values CollectEntries WithIndex Flatten nested collections
Object Model
Groovy classes Properties and generated accessors Named argument constructors Traits Interfaces Enums Method overloading Operator overloading Categories with use Extension methods
Metaprogramming
Expando ExpandoMetaClass methodMissing propertyMissing InvokeMethod GetProperty interception AST transform @ToString AST transform @Immutable AST transform @Canonical CompileStatic
Files Data and XML
File text reading File line iteration Writing files JsonSlurper parsing JsonOutput serialization XmlSlurper parsing MarkupBuilder XML ConfigSlurper URL text reading Process execution
Concurrency Testing Build
GPars-style parallel collection concept Synchronized methods Thread start helper ExecutorService interop Spock specification structure GroovyTestCase Exception assertions Gradle Groovy DSL Grab dependencies Logging with @Slf4j
Groovy / Collections

GroupBy

Learn GroupBy in Groovy through a focused explanation, a dedicated topic-specific example, an engineering boundary, and a mastery check.

12 min read • Intermediate

GroupBy is a focused Groovy lesson inside Collections. The example uses the construct named in the lesson directly rather than reusing a generic placeholder.

Trace the example from its inputs through GroupBy and identify the behavior that would change if that construct were removed or replaced. Pay attention to the language-specific rules shown by the syntax, because neighboring lessons intentionally exercise different mechanisms.

Topic-specific example

groovy-0035-eb851e6674.groovy
groovy Try It Live 
def sample36 = [36, 37, 38]
println sample36.sum() // GroupBy
Edge case / engineering note

For GroupBy, test one realistic boundary: empty data, invalid input, unavailable resources, lifetime/cleanup, type constraints, or concurrency timing where applicable. A successful happy path is not enough to prove the construct is used correctly.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

GroupBy Mastery Check →
← PREVIOUS
Inject reduction
NEXT →
Sort with closure