On my system (Win 10, JRE 1.8.0, Android Studio 3.1.2, Gradle 4.1) there is no 

tools.jar in the JRE directory (C:\Program Files\Java\jre1.8.0_171).

​

However, I found it in C:\Program Files\Android\Android Studio\jre\lib and 

tried setting JAVA_HOME=C:\Program Files\Android\Android Studio\jre

​

That works (for me)!

on linux -> you need

1) to install openjdk :

sudo apt-get install openjdk-8-jdk

2) export jdk location : 

export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64

You should not alter gradle.properties manually. Try setting your 

JAVA_HOME in ~/.zshrc to something like-

​

export JAVA_HOME="/Applications/Android Studio.app/Contents/jre/jdk/Contents/Home"

​

then relaunch a terminal session

On my system (Win 10, JRE 1.8.0, Android Studio 3.1.2, Gradle 4.1) there is no tools.jar in the JRE directory (C:\Program Files\Java\jre1.8.0_171).

​

However, I found it in C:\Program Files\Android\Android Studio\jre\lib and tried setting JAVA_HOME=C:\Program Files\Android\Android Studio\jre