In the actual development process, we may need to change the JDK version due to the needs of the project. However, an error will be reported after replacement, as follows:

Java compiler level does not match the version of the installed Java project facet.

Solution:

Step 1: set the eclipse JDK version

Windows—-> Preferences—-> Java—-> Installed JREs

Step 2: set the JDK compiled version

Windows—-> Preferences—-> Java—-> Compiler

Step 3: right click the project and set the JDK version of the project to the above unified version

Right click the item – > Properties—-> Java Compiler

  Note: the above versions should be unified