Introduction

Groovy… * is an agile and dynamic language for the Java Virtual Machine * builds upon the strengths of Java but has additional power features inspired by languages like Python, Ruby and Smalltalk * makes modern programming features available to Java developers with almost-zero learning curve * provides the ability to statically type check and statically compile your code for robustness and performance * supports Domain-Specific Languages and other compact syntax so your code becomes easy to read and maintain * makes writing shell and build scripts easy with its powerful processing primitives, OO abilities and an Ant DSL * increases developer productivity by reducing scaffolding code when developing web, GUI, database or console applications * simplifies testing by supporting unit testing and mocking out-of-the-box * seamlessly integrates with all existing Java classes and libraries * compiles straight to Java bytecode so you can use it anywhere you can use Java

1. Groovy Language Specification

1.1. Syntax

This chapter covers the syntax of the Groovy programming language. The grammar of the language derives from the Java grammar, but enhances it with specific constructs for Groovy, and allows certain simplifications.

1.1.1. Comments

Single line comment

Multiline comment

JavaDoc comment

Shebang line

1.1.2. Keywords

1.1.3. Identifiers

Normal identifiers

Identifiers start with a letter, a dollar or an underscore. They cannot start with a number.

A letter can be in the following ranges:

a to z (lowercase ascii letter)
A to Z (uppercase ascii letter)
\u00C0 to \u00D6
\u00D8 to \u00F6
\u00F8 to \u00FF
\u0100 to \uFFFE

Then following characters can contain letters and numbers.

Here are a few examples of valid identifiers (here, variable names):

def name
def item3
def with_underscore
def $dollarStart

But the following ones are invalid identifiers:

def 3tier
def a+b
def a#b

Quoted identifiers

1.1.4. Strings

Single quoted string

Double quoted string

Triple single quoted string

Triple double quoted string

Slashy string

Dollar slashy string

1.1.5. Numbers

Integer literal

Floating point literal

Binary literal

Octal literal

Hexadecimal literal

Underscore in literal

Number type suffixes

1.1.6. Booleans

1.1.7. Arrays

1.1.8. Lists

1.1.9. Maps

String keys

Parenthesized keys

1.2. Semantics

This chapter covers the semantic of the Groovy programming language.

1.2.1. Typing

Optional typing

Static type checking

Static compilation

1.2.2. Statements

Variable definition

Variable assignment

Multiple assignment

Control structures

Conditional structures

if / else

switch / case

Looping structures

Classic for loop

for in loop

while loop

Exception handling

try / catch / finally

Multi-catch

Power assertion

Labeled statements

1.2.3. Expressions

GPath expressions

1.2.4. Promotion and coercion

Number promotion

Closure to type coercion

Map to type coercion

String to enum coercion

1.2.5. Optionality

Optional parentheses

Optional semicolons

Optional return keyword

Optional public keyword

1.2.6. The Groovy Truth

Customizing the truth with asBoolean() methods

1.3. Operators

This chapter covers the operators of the Groovy programming language.

1.3.1. Arithmetic operators

1.3.2. Bitwise and logical operators

1.3.3. Conditional operators

Not operator

Ternary operator

Elvis operator

1.3.4. Object operators

Safe navigation operator

Direct field access operator

Method reference operator

1.3.5. Regular expression operators

Pattern operator

Find operator

Match operator

1.3.6. Other operators

Spread operator

Spreading method arguments

Spread list elements

Spread map elements

Range operator

Spaceship operator

Subscript operator

Membership operator

Identity operator

Coercion operator

Diamond operator

Call operator

1.3.7. Operator precedence

1.3.8. Operator overloading

1.4. Program structure

This chapter covers the program structure of the Groovy programming language.

1.4.1. Package name

1.4.2. Imports

Default imports

Simple import

Star import

Static import

Static star import

Import aliasing

1.4.3. Scripts versus classes

1.4.4. Initializers

Static initializers

Instance initializers

1.5. Object orientation

This chapter covers the object orientation of the Groovy programming language.

1.5.1. Types

Primitive types

Class

Normal class

Static class

Inner class

Anonymous inner class

Abstract class

Interface

Annotation

Closure annotation parameters

Meta-annotations

Annotation placement

Constructors

Named argument constructor

Methods

Method definition

Named arguments

Default arguments

Varargs

Method selection algorithm

Exception declaration

Fields and properties

Fields

Properties

Inheritance

Generics

1.6. Closures

This chapter covers Groovy Closures.

1.6.1. Syntax

1.6.2. Parameters

Normal parameters

Implicit parameter

Default parameter

Varargs

1.6.3. Delegation strategy

1.6.4. Closures in GStrings

1.6.5. Functional programming

Currying

Left currying

Right currying

Index based currying

Memoization

Composition

Trampoline

2. Tools

2.1. groovyc, the Groovy compiler

2.1.1. Ant task

2.1.2. Maven integration

GMaven and GMavenPlus

The Groovy Eclipse Maven plugin

2.1.3. Command-line compiler

2.1.4. Joint compilation

2.2. groovysh, the Groovy shell

2.3. groovyConsole, the Groovy swing console

2.4. groovydoc, the Groovy & Java documentation generator

2.5. IDE integration

3. User Guides

3.1. Getting started

3.1.1. Download Groovy

3.1.2. Install Groovy

3.2. Differences with Java

3.2.1. Multi-methods

3.2.2. Array initializers

3.2.3. Package scope visibility

3.2.4. ARM blocks

3.2.5. Inner class instantiation

3.3. Groovy Development Kit

3.3.1. Working with IO

3.3.2. Working with collections

3.3.3. Handy utilities

ConfigSlurper

Expando

Observable list, map and set

3.4. Metaprogramming

3.4.1. Runtime metaprogramming

GroovyObject interface

invokeMethod

get/setProperty

get/setMetaClass

get/setAttribute

propertyMissing

methodMissing

GroovyInterceptable

Metaclasses

Custom metaclasses

Delegating metaclass

Magic package

Per instance metaclass

ExpandoMetaClass

Constructors

Borrowing methods

Dynamic method names

GroovyObject methods

Overriding static invokeMethod

Properties

Runtime discovery

Static methods

Extension modules

Module descriptor

Instance methods

Static methods

3.4.2. Compile-time metaprogramming

Developing AST transformations

Compilation phases guide

Local transformations

Global transformations

AST API guide

Testing AST transformations

Available AST transformations

Binding

@Bindable

@Vetoable

Beans related

Constructors

@TupleConstructor

@InheritConstructors

@Singleton

@IndexedProperty

@ToString

@EqualsAndHashCode

@Canonical

@Immutable

@PackageScope

@Field

@ListenerList

Synchronization and locking

@Sinchronized

@WithReadLock

@WithWriterLock

Static typing and compilation

@TypeChecked

Custom type checking extensions

@CompileStatic

@CompileDynamic

Logging

@Log

@Commons

@Slf4j

@Log4j

@ASTTest

Metaprogramming

@Category

@Mixin

Execution control

@ThreadInterrupt

@TimedInterrupt

@ConditionalInterrupt

Other

@Grab

@GrabResolver

@GrabExclude

@Delegate

@Lazy

@Memoized

@AutoClone

@AutoExternalizable

@Newify

Groovy Language Documentation

Introduction

1. Groovy Language Specification

1.1. Syntax

1.1.1. Comments

Single line comment

Multiline comment

JavaDoc comment

Shebang line

1.1.2. Keywords

1.1.3. Identifiers

Normal identifiers

Quoted identifiers

1.1.4. Strings

Single quoted string

Double quoted string

Triple single quoted string

Triple double quoted string

Slashy string

Dollar slashy string

1.1.5. Numbers

Integer literal

Floating point literal

Binary literal

Octal literal

Hexadecimal literal

Underscore in literal

Number type suffixes

1.1.6. Booleans

1.1.7. Arrays

1.1.8. Lists

1.1.9. Maps

String keys

Parenthesized keys

1.2. Semantics

1.2.1. Typing

Optional typing

Static type checking

Static compilation

1.2.2. Statements

Variable definition

Variable assignment

Multiple assignment

Control structures

Conditional structures

Looping structures

Exception handling

try / catch / finally

Multi-catch

Power assertion

Labeled statements

1.2.3. Expressions

GPath expressions

1.2.4. Promotion and coercion

Number promotion

Closure to type coercion

Map to type coercion

String to enum coercion

1.2.5. Optionality

Optional parentheses

Optional semicolons

Optional return keyword

Optional public keyword

1.2.6. The Groovy Truth

Customizing the truth with asBoolean() methods

1.3. Operators

1.3.1. Arithmetic operators

1.3.2. Bitwise and logical operators

1.3.3. Conditional operators

Not operator

Ternary operator

Elvis operator

1.3.4. Object operators

Safe navigation operator

Direct field access operator

Method reference operator

1.3.5. Regular expression operators

Pattern operator

Find operator

Match operator