Java In A Nutshell, 5th Edition

Every Java class file contains a version number that specifies the version of the class file format. This error is thrown when the Java Virtual Machine attempts to read a class file with a version number it does not support.

public class UnsupportedClassVersionError extends ClassFormatError { // Public Constructors public UnsupportedClassVersionError ( ); public UnsupportedClassVersionError (String s ); }