$ mkdir /opt/gradle
$ unzip -d /opt/gradle gradle-6.6.1-bin.zip
$ ls /opt/gradle/gradle-6.6.1
LICENSE NOTICE bin getting-started.html init.d lib media
Open the Gradle folder and copy the path to "bin" folder of Gradle like "...\gradle\gradle-6.6.1\bin." to your system variables.
$ export PATH=$PATH:/opt/gradle/gradle-6.6.1/bin
download it from here https://developer.android.google.cn/studio#downloads
If you are looking to download a research paper which is not available on internet as Open access,
For testing your Android applications, you will need a virtual Android device which can help you to quickly test your application on your system instead of using any mobile phone. Let us create an Android virtual device. Launch Android AVD Manager by Clicking AVD_Manager icon as shown below
After Click on a virtual device icon, it will show by default virtual devices which are available on SDK, and you can create new bty clicking "Create Virtual Device" button.