The following is the first few sections of a chapter from The Busy Coder's Guide to Android Development, plus headings for the remaining major sections, to give you an idea about the content of the chapter.

Introducing Gradle and the Manifest

In the discussion of Android Studio, this book has mentioned something called “Gradle”, without a lot of explanation.

In this chapter, the mysteries of Gradle will be revealed to you.

(well, OK, some of the mysteries…)

We also mentioned in passing in the previous chapter the concept of the “manifest” — AndroidManifest.xml — as being a special file in our Android projects.

On the one hand, Gradle and the manifest are not strictly related. On the other hand, some (but far from all) of the things that we can set up in the manifest can be overridden in Gradle.

So, in this chapter, we will review both what Gradle is, what the manifest is, what each of their roles are, and the basics of how they tie together.

Gradle: The Big Questions

First, let us “set the stage” by examining what this is all about, through a series of fictionally-asked questions (FAQs).

What is Gradle?

Gradle is software for building software, otherwise known as “build automation software” or “build systems”. You may have used other build systems before in other environments, such as make (C/C++), rake (Ruby), Ant (Java), Maven (Java), etc.

These tools know — via intrinsic capabilities and rules that you teach them — how to determine what needs to be created (e.g., based on file changes) and how to create them. A build system does not compile, link, package, etc. applications directly, but instead directs separate compilers, linkers, and packagers to do that work.

Gradle uses a domain-specific language (DSL) built on top of Groovy to accomplish these tasks.

What is Groovy?

There are many programming languages that are designed to run on top of the Java VM. Some of these, like JRuby and Jython, are implementations of other common programming languages (Ruby and Python, respectively). Other languages are unique, and Groovy is one of those.

Groovy scripts look a bit like a mashup of Java and Ruby. As with Java, Groovy supports:

As with Ruby, though:

Groovy is an interpreted language, like Ruby and unlike Java. Groovy scripts are run by executing a groovy command, passing it the script to run. The Groovy runtime, though, is a Java JAR and requires a JVM in order to operate.

One of Groovy’s strengths is in creating a domain-specific language (or DSL). Gradle, for example, is a Groovy DSL for doing software builds. Gradle-specific capabilities appear to be first-class language constructs, generally indistinguishable from capabilities intrinsic to Groovy. Yet, the Groovy DSL is largely declarative, like an XML file.

To some extent, we get the best of both worlds: XML-style definitions (generally with less punctuation), yet with the ability to “reach into Groovy” and do custom scripting as needed.

What Does Android Have To Do with Gradle?

Google has published the Android Gradle Plugin, which gives Gradle the ability to build Android projects. Google is also using Gradle and the Android Gradle Plugin as the build system behind Android Studio.

Obtaining Gradle

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Versions of Gradle and the Android Gradle Plugin

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Gradle Environment Variables

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Examining the Gradle Files

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Introducing the Manifest

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Things In Common Between the Manifest and Gradle

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Other Gradle Items of Note

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Where’s the GUI?

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The Rest of the Manifest

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Learning More About Gradle

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Visit the Trails!

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