Build Tools
Build tools are programs that automate the creation of executable applications from source code(.War,.Jar,.apk for android app)
Building incorporates compiling,linking and packaging the code into a usable or executable form.
Basically build automation is the act of scripting or automating a wide variety of tasks that software developers do in their day-to-day activities like:
Maven Central
Maven Central is an open repository provided by the company Sonatype. This repository hosts libraries which can be used in your build. By default, a Maven build uses Maven Central to search for required libraries.
https://mvnrepository.com/
JCenter
https://bintray.com/bintray/jcenter
Gradle is an advanced general purpose build management system based on Groovy and Kotlin. Gradle supports the automatic download and configuration of dependencies or other libraries. It supports Maven and Ivy repositories for retrieving these dependencies. This allows reusing the artifacts of existing build systems.
Gradle supports multi-project and multi-artifact builds.