如果您只是使用 javac 1.6的默认值，您的类文件将无法在旧版本的Java上运行。

If you just build with the defaults of javac 1.6, your class files will not work on old versions of Java.

***方式编译旧Java只是为了使用较旧的JDK版本。但如果你真的想尝试从较新的Java编译，这里有一些说明：

The best way to compile for older Java is just to use the older JDK releases. But if you really want to try to compile for older Java from newer, here are some instructions:

• 如何对旧平台版本进行交叉编译


• 源，目标，类文件版本解码器环

• How to cross-compile for older platform versions
• Source, target, class file version decoder ring