Java projects can be compiled and run normally, but a red fork __java is always present

This is a very maddening question. Clearly can be normal compilation, operation, but the old has a small red fork. To solve a half-day, or to finish. Thought anyway can run normally, regardless of it, but every time I see that Red fork there, in the mind very uncomfortable. Today we finally found a solution.

reason

Java compiler level dose not match the version of the installed Java Project facet ( The Java compiler level does not match the version of the Java project), the problem is that the level of the Java compiler and the Java-level inconsistency set in Java project facet.

Way to solve

Right Key project, click "Properties", then click "Project Facets" on the left side, and then set the level of Java on the right side to be the same as the Java compiler.

Also be consistent with the version in the. settings/org.eclipse.wst.common.project.facet.core.xml file in the project root directory, as shown in

Then the problem can be solved.