Gradle Properties

Gradle supports properties in builds just like Maven does, but the actual documentation and examples are harder to come by. This article will show you something that actually works.
In Maven, you typically have a dependencyManagement section that declares the dependencies with versions; I typically put the versions in a properties block so that they’re all located in a nice, handy, easy-to-manage place. See https://github.com/jottinger/ml/blob/master/pom.xml for a simple example; it’s not consistent with the property usage, but the idea should be clear. I have my versions all coalesced into an easy place to update them, and the changes propagate through the entire project.
Gradle examples rarely do anything like this. Therefore, for your edification, here’s a simple example:
gradle.properties:

aws_sdk_version=1.11.377
kotlin_version=1.2.50

build.gradle:

buildscript {
  repositories {
    mavenCentral()
  }
  dependencies {
    classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
  }
}
apply plugin: 'java'
apply plugin: 'kotlin'
repositories {
    mavenCentral()
    jcenter()
}
dependencies {
    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8"
    compile "com.amazonaws:aws-java-sdk:$aws_sdk_version"
}
tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
    kotlinOptions {
        jvmTarget = "1.8"
        javaParameters = true
    }
}

You can use a constraints block in the dependencies to do the same thing as dependencyManagement in Maven; that would look like this:

dependencies {
    constraints {
        implementation "com.amazonaws:aws-java-sdk:$aws_sdk_version"
    }
}

This would allow submodules (or this module) to use a simpler dependency declaration, leaving off the version, just like Maven can do:

dependencies {
    compile "org.jetbrains.kotlin:kotlin-stdlib-jdk8"
    compile "com.amazonaws:aws-java-sdk"
}

If you don’t want to use gradle.properties, that’s doable too (as pointed out by channel member matsurago) – you can put it in the buildscript block, as so:

buildscript {
  ext.aws_sdk_version="1.11.377"
}