Each java class has a version stamp, older versions have lower numbers. The JVM is backward compatible, so older classes also run in a newer JVM. Version ranges are as follows:

Java 1.1 platform: 45.3-45.65535
Java 1.2 platform: 45.3-46.0
Java 1.3 platform: 45.3-47.0
Java 1.4 platform: 45.3-48.0

Java 5 class files are stamped with 49.0, and the JVM is also backward compatible. So, a 1.3 class file will run in a 1.5 JVM, but not the other way round.

注冊表HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft下也有關于jdk和jre的設置

以上可以幫助解決Unsupported major.minor version 49.0問題