Warning major version 52 is newer than 51, the highest major version supported by this compiler

Solution 1:

I was having the same issue, and tearing my hair out. I had the JDK Version 8 installed, but these warnings wouldn't go away, and eventually they generated a build-breaking error.

When I went to Tools -> Options -> Xamarin, and looked at the Android Settings, the Java Development Kit Location was pointing to jdk.1.7.xxxx, in Program Files (x86).

I changed it to 1.8.0_101, in Program Files. Then I restarted Visual Studio, and the same error happened again. Somehow, Visual Studio was detecting Version 7 of the JDK and pointing it to that automatically.

So the solution turned out to be very simple. As well as installing Version 8 of the JDK, UNINSTALL Version 7 of the JDK. As soon as I did that, Xamarin turned out to be much better behaved. This step solved a whole bunch of seemingly unrelated problems.

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Solution 2:

That error is telling you that the Java Class version that is being loaded was compiled with Java 8 (52) but Java 7 (51) is trying to load that compiled class.

Java 7 uses major version 51
Java 8 uses major version 52

Check which Java version(s) are installed on your machine and review Xamarin's requirements and Java installation steps (linked below)

Installing the Java SDK (JDK)

Solution 3:

For people having problems with setting the appropriate JDK version, you might want to try to override this setting in the vs2015 options dialog:

Cross Platform Dialog

Solution 4:

Delete bin folder and obj folder and run the project it will be work fine

Solution 5:

You have a bad proguard.jar file, you need to replace this .jar by a correct version. The steps below describing how to do that. Some colleagues had the same problem here.

Go to Preferences => SDK locations and copy the Android SDK location.
Go to that folder (mostly /Users/USERNAME/Library/Developer/Xamarin/android-sdk-macosx) and go to the folder tools/proguard/lib.
Here you find a proguard.jar.
Rename this to proguard_OLD.jar.
Download the last proguard file (like this one https://sourceforge.net/projects/proguard/files/)
Unzip and place the proguard.jar in the tools/proguard/lib folder
Rebuild your Project

Everything should be fixed!

You can find more info about the bug here:

https://releases.xamarin.com/technical-bulletin-android-sdk-build-tools-24/