React Native: Could not find tools.jar

* What went wrong:
Execution failed for task ‘:app:compileDebugJavaWithJavac’.
> Could not find tools.jar. Please check that C:\Program Files\Java\jre1.8.0_161 contains a valid JDK installation.

Solution:

Setting the missing “JAVA_HOME” system environment variable worked for me.

Press WIN+Pause on keyboard.
Click advanced system settings.
Click “Environment variables”.
Click “New” under “System variables”.
Type “JAVA_HOME” in the Variable name field.
Type the path to the JDK in the Value field. For me the correct path with short filename was “C:\PROGRA~1\Java\jdk1.8.0_66”. Your path will vary depending on the installed version.
Click OK, and OK in previous window too.
Restart any command prompts or restart the computer.
react-native run-android worked fine after that.

https://stackoverflow.com/questions/35278283/could-not-find-tools-jar-react-native-android-in-windows-10