This problem is caused by a Java class file compiled by a higher version of JDK trying to run on a lower version of JVM.

1. The solution is to ensure that the versions of JVM (Java command) and JDK (javac command) are consistent. If it is the Linux version, enter the Java – version and javac – version commands in the command line to see if the versions are consistent. I use 1.7.0_ 80。

2. The same version still can’t solve the problem. I don’t compile with javac directly from the command line, but with eclipse compiler. Because many compilers come with javac, rather than using the compiler in the operating system. If your compiler is eclipse, you need to set the JDK version in the properties of the project. The method is to right-click the project — & gt; properties — & gt; Java compiler — & gt; enable project specific settings — & gt; and set the compiler compliance level to 1.7, which is the version consistent with the JVM (the version shown by Java – version in the command line). Because of the need to be compatible with other software before, I reduced the Java version from 1.8 to 1.7, but eclipse did not move, so after opening it, I found that the default was 1.8, so I manually reduced it to 1.7, recompiled it, and finally passed!

To sum up, if you are compiling with a compiler, make sure that the JDK version of the compiler is consistent with the Java version of the operating system.

The screenshot is as follows: