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
* @param scope the scope that limits which types are included
	 * @param style flags defining the style of the dialog; the only valid values are
	 *   <code>IJavaElementSearchConstants.CONSIDER_CLASSES</code>,
	 *   <code>CONSIDER_INTERFACES</code>, or their bitwise OR 
	 *   (equivalent to <code>CONSIDER_TYPES</code>)
	 * @param multipleSelection <code>true</code> if multiple selection is allowed
	 * @return a new selection dialog
	 * @exception JavaModelException if the selection dialog could not be opened
	 */
	public static SelectionDialog createTypeDialog(Shell parent, IRunnableContext context, IJavaSearchScope scope, int style, boolean multipleSelection) throws JavaModelException {
		return createTypeDialog(parent, context, scope, style, multipleSelection, "");
	}
		
	/**
	 * Creates a selection dialog that lists all types in the given scope containing 
	 * a standard <code>main</code> method.
	 * The caller is responsible for opening the dialog with <code>Window.open</code>,
	 * and subsequently extracting the selected type(s) (of type
	 * <code>IType</code>) via <code>SelectionDialog.getResult</code>.
	 * 
	 * @param parent the parent shell of the dialog to be created
	 * @param context the runnable context used to show progress when the dialog
	 *   is being populated
	 * @param scope the scope that limits which types are included
	 * @param style flags defining the style of the dialog; the only valid values are
	 *   <code>IJavaElementSearchConstants.CONSIDER_BINARIES</code>,
	 *   <code>CONSIDER_EXTERNAL_JARS</code>, or their bitwise OR, or <code>0</code>
	 * @param multipleSelection <code>true</code> if multiple selection is allowed
	 * @param filter the initial pattern to filter the set of types containg a main method. For 
	 * example "App" shows all types starting with "app". The meta character '?' representing