尽管从理论上讲，使用复杂的工具可以将为JDK 11编译的类转换为JDK 8，但这并非微不足道。二进制级别有重大变化。

While conversion of classes compiled for JDK 11 to JDK 8 would be theoretically possible with a sophisticated tool, it’s not trivial. There are significant changes on the binary level.

首先，JDK 11引入了嵌套类型，这样就无需在访问 private 时生成综合访问器方法内部/外部类的成员。当然，这种访问在旧版本中将失败。

First, JDK 11 introduced nest types, which eliminates the need to generate synthetic accessor methods when accessing private members of inner/outer classes. Of course, such access would fail in older versions.

它还引入了动态常量，尽管我不知道Java语言是否在任何地方都利用了该功能。

It also introduced dynamic constants, though I don’t know whether the Java language exploits that feature anywhere. This is mainly intended for future versions.

然后，由于JDK 9，使用 invokedynamic 引用 java Java 8中不存在的.lang.invoke.StringConcatFactory 。

Then, since JDK 9, string concatenation gets compiled using invokedynamic referring to java.lang.invoke.StringConcatFactory which is not present in Java 8.

一个可行的功能是 private 接口中的方法，作为语言功能在Java 9中引入，但已经在Java 8中以二进制级别进行了处理。

A feature that could work, is private methods in interfaces, introduced in Java 9 as a language feature, but already handled on the binary level in Java 8.

Java 8也将无法处理模块定义，但我想，它们将被忽略。

Java 8 would also be unable to process module definitions, but I suppose, they would be ignored.