What happens when eclipse imports another project and discovers that the JDK version is different?

Original: https://www.cnblogs.com/chenmingjun/p/8472885.html

When we import other people's projects, we find that the JDK version of the imported project is different from the version we use on the computer, how to solve it?

Select the project right-----and Build Path--Check the Libraries column to remove the library option.

Then add a new library option:

ADD Library ...--JRE System Library---next---execution environment--and environments ...-select JavaSE-9 (jdk-9.0.4)--Apply and Close.

or right-click the JRE System library[javase-1.7]--Properties--execution environment--and environments ...-select Javas E-9 (jdk-9.0.4)---Apply and Close.

The exact operation is as follows:

What happens when eclipse imports another project and discovers that the JDK version is different?