Bug 19886 setProjectJavadocLocation() only in internal package [api] [javadoc]
If You want to set the project javadoc location by API so You have to use an internal class, there is no public interface. see class org.eclipse.jdt.internal.corext.javadoc.JavaDocLocations (Otherwise the method setLibraryJavadocLocation() is public at org.eclipse.jdt.ui.JavaUI - thats ok.)
org.eclipse.jdt.ui/ui/org/eclipse/jdt/ui/JavaUI.java
/** 
	 * Reveals the given java element  in the given editor. If the element is not an instance
	 * of <code>ISourceReference</code> this method result in a NOP. If it is a source
	 * reference no checking is done if the editor displays a compilation unit or class file that 
	 * contains the source reference element. The editor simply reveals the source range 
	 * denoted by the given element.
	 * 
	 * @param part the editor displaying a compilation unit or class file
	 * @param element the element to be revealed
	 * 
	 * @since 2.0
	 */
	public static void revealInEditor(IEditorPart part, IJavaElement element) {
		EditorUtility.revealInEditor(part, element);
	}
	 
	/**
	 * Returns the working copy manager for the Java UI plug-in.
	 *
	 * @return the working copy manager for the Java UI plug-in
	 */
	public static IWorkingCopyManager getWorkingCopyManager() {
		return JavaPlugin.getDefault().getWorkingCopyManager();
	}
	
	/**
	 * Answers the shared working copies currently registered for the Java plug-in. 
	 * 
	 * @return the list of shared working copies this plug-in