# Part 5: Exploring Incremental Builds

version 9.6.1

Learn the basics of Gradle’s incremental builds.

In this section you will:

- Use Gradle properties

- Understand incremental builds

- Explore task outcome labels

## Step 0. Before you Begin

1. You initialized your Java app in part 1.

2. You ran several tasks in part 2.

3. You learned about dependency management in part 3.

4. You applied a plugin to your app in part 4.

## Step 1. Understanding Incremental Builds

It’s important to know that Gradle optimizes your build in a variety of ways. One such optimization is called incremental builds.

An incremental build is a build that avoids running tasks whose inputs did not change since the previous build, making the execution of such tasks unnecessary.

For incremental builds to work, tasks must define their inputs and outputs. At build time, Gradle will determine whether the input or outputs have changed. If they have changed, Gradle will execute the task. Otherwise, it will skip execution.

## Step 2. Updating Gradle Properties

To better see incremental builds in action, we are going to switch the console output to verbose.

In the top-level folder of your app (`tutorial`), create a `gradle.properties` file:

    $ touch gradle.properties

Add `org.gradle.console=verbose` so the contents of the file look like this:

gradle.properties

    org.gradle.console=verbose

## Step 3. Analyzing Incremental Builds

Run the clean task and then the build task using the `./gradlew :app:clean :app:build` command:

    $ ./gradlew :app:clean :app:build

    > Task :app:clean
    > Task :app:compileJava
    > Task :app:processResources NO-SOURCE
    > Task :app:classes
    > Task :app:jar
    > Task :app:startScripts
    > Task :app:distTar
    > Task :app:distZip
    > Task :app:assemble
    > Task :app:compileTestJava
    > Task :app:processTestResources NO-SOURCE
    > Task :app:testClasses
    > Task :app:test
    > Task :app:check
    > Task :app:build

    BUILD SUCCESSFUL in 1s
    8 actionable tasks: 8 executed

No surprise here, Gradle invoked all the tasks needed to build the app. This was done successfully.

Run the build again to view the incremental build optimization in action:

    $ ./gradlew :app:build

    > Task :app:compileJava UP-TO-DATE
    > Task :app:processResources NO-SOURCE
    > Task :app:classes UP-TO-DATE
    > Task :app:jar UP-TO-DATE
    > Task :app:startScripts UP-TO-DATE
    > Task :app:distTar UP-TO-DATE
    > Task :app:distZip UP-TO-DATE
    > Task :app:assemble UP-TO-DATE
    > Task :app:compileTestJava UP-TO-DATE
    > Task :app:processTestResources NO-SOURCE
    > Task :app:testClasses UP-TO-DATE
    > Task :app:test UP-TO-DATE
    > Task :app:check UP-TO-DATE
    > Task :app:build UP-TO-DATE

    BUILD SUCCESSFUL in 409ms
    7 actionable tasks: 7 up-to-date

Most tasks now have the `UP-TO-DATE` label. This is how Gradle lets us know that inputs and outputs have not changed and therefore some tasks did not re-run.

## Step 4. Understanding Outcome Labels

There are four labels that developers can use to view task outcomes when verbose mode is turned on:

Outcome Label | Description
--- | ---
UP-TO-DATE | Task that has been already executed and hasn’t changed (incremental build feature)
SKIPPED | Task was explicitly prevented from running
FROM-CACHE | Task output has been copied to local directory from previous builds in the build cache (caching feature)
NO-SOURCE | Task was not executed because its required inputs were not available

If there is no label, the task was newly executed by Gradle (locally).

We will look at the `FROM-CACHE` label in the next section.

Next Step: Enabling the Build Cache >>