This compilation unit is not on the build path of a Java project

问题

When I try to use ctrl+space this error is shown:

This compilation unit is not on the build path of a Java project.

I see that there are similar topics but my work environment is Eclipse and i pull my project from Git (I import project as general project) and i use Apache Ant. Can anyone help me?

回答1:

Since you imported the project as a General Project, it does not have the java nature and that is the problem.

Add the below lines in the .project file of your workspace and refresh.

<natures>
      <nature>org.eclipse.jdt.core.javanature</nature>
</natures>

回答2:

If it is a Maven project then sometimes re-importing of it helps:

1. Right-click the project in the Project Explorer and choose Delete.
2. File > Import... > Maven > Existing Maven Projects > Next > Root Directory > Browse your project from Disk.

Hope it will resolve the issue.

回答3:

Go to Project-> right Click-> Select Properties -> project Facets -> modify the java version for your JDK version you are using.

回答4:

Another alternative to Loganathan Mohanraj's solution (which effectively does the same, but from the GUI):

1. Right-Click on your project
2. Go to "Properties"
3. Choose "Project Natures"
4. Click on "Add"
5. Choose "Java"
6. Click "Apply and Close"

回答5:

Add this to .project file

 <?xml version="1.0" encoding="UTF-8"?>
        <projectDescription>
            <name>framework</name>
            <comment></comment>
            <projects>
            </projects>
            <buildSpec>
                <buildCommand>
                    <name>org.eclipse.wst.common.project.facet.core.builder</name>
                    <arguments>
                    </arguments>
                </buildCommand>
                <buildCommand>
                    <name>org.eclipse.jdt.core.javabuilder</name>
                    <arguments>
                    </arguments>
                </buildCommand>
                <buildCommand>
                    <name>org.eclipse.m2e.core.maven2Builder</name>
                    <arguments>
                    </arguments>
                </buildCommand>
                <buildCommand>
                    <name>org.eclipse.wst.validation.validationbuilder</name>
                    <arguments>
                    </arguments>
                </buildCommand>
            </buildSpec>
            <natures>
                <nature>org.eclipse.jem.workbench.JavaEMFNature</nature>
                <nature>org.eclipse.wst.common.modulecore.ModuleCoreNature</nature>
                <nature>org.eclipse.jdt.core.javanature</nature>
                <nature>org.eclipse.m2e.core.maven2Nature</nature>
                <nature>org.eclipse.wst.common.project.facet.core.nature</nature>
            </natures>
        </projectDescription>

来源：https://stackoverflow.com/questions/25401124/this-compilation-unit-is-not-on-the-build-path-of-a-java-project