Gradle Recipes for Android

Appendix A. Just Enough Groovy to Get By

This appendix reviews the basics of the Groovy programming language. The Gradle build files consist largely of a Domain Specific Language, written in Groovy, for builds. In addition to the DSL, any legal Groovy code can be added to the build.

Groovy is a general-purpose programming language, based on Java, that compiles to Java byte codes. While it has functional capabilities, it is an object-oriented language that is arguably the next-generation language in the path from C++ to Java.

Basic Syntax

The “Hello, World!” program for Groovy is the one-liner shown in Example A-1.

Example A-1. Hello, World! in Groovy

println 'Hello, World!'

Items of note:

• Semicolons are optional. If you add them, they work, but they’re not required.

• Parentheses are optional until they’re not. If the compiler guesses correctly where they should have gone, everything works. Otherwise, add them back in. The println method takes a String argument. Here the parentheses are left out.

• There are two types of strings in Groovy: single-quoted strings, like Hello, are instances of java.lang.String. Double-quoted strings are Groovy strings and allow interpolation, shown in Example A-2.

There are no “primitives” in Groovy. All variables use the wrapper classes, like java.lang.Integer, java.lang.Character, and java.lang.Double. The native data type for integer literals, like 3, is Integer. The native data type for floating point literals, like 3.5, is java.math.BigDecimal ...