Close your project and Modify two files
.project
- Delete any
<buildCommand>...<buildCommand/>
Android related - Delete
<nature>com.android.ide.eclipse.adt.AndroidNature</nature>
.classpath
- Delete any
<classpathentry .. />
Android related - Add
<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.6"/>
Finally clean your project from any folder or other things Android related and reopen your project and you should notice that the project is converted to a Java Project