Are you using the wrong java sdk? what’s your version & unity version?
If your unity unity 2017+ and getting this just remove JDK 9 and install JDK 8. You also need to tell the Unity editor to use JDK 8. If you have JDK 7, remove that and install JDK 8.
Here official info from Unity: Java 9 (JDK 9) support by Unity Android
Maybe change your title with the error to help others who encounter this.