Bug 15604 Promote Fill arguments on method completion to a real preference
It is still in work in progress but it has become an established feature by now. Promote the preference to the code assist preference page.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/text/java/JavaCompletionProcessor.java
fExperimentalCollector.reset(offset, unit.getJavaProject(), fAllowAddImports ? unit : null);
					fExperimentalCollector.setViewer(viewer);
					
					Point selection= viewer.getSelectedRange();
					if (selection.y > 0)
						fExperimentalCollector.setReplacementLength(selection.y);
					
					unit.codeComplete(offset, fExperimentalCollector);
				}
			} catch (JavaModelException x) {
				Shell shell= viewer.getTextWidget().getShell();
				ErrorDialog.openError(shell, JavaTextMessages.getString("CompletionProcessor.error.accessing.title"), JavaTextMessages.getString("CompletionProcessor.error.accessing.message"), x.getStatus()); 
			}				
			results= fExperimentalCollector.getResults();
		} else {
			try {
				if (unit != null) {
	
					fCollector.reset(offset, unit.getJavaProject(), fAllowAddImports ? unit : null);
					Point selection= viewer.getSelectedRange();
					if (selection.y > 0)
						fCollector.setReplacementLength(selection.y);
					
					unit.codeComplete(offset, fCollector);
				}
			} catch (JavaModelException x) {
				Shell shell= viewer.getTextWidget().getShell();
				ErrorDialog.openError(shell, JavaTextMessages.getString("CompletionProcessor.error.accessing.title"), JavaTextMessages.getString("CompletionProcessor.error.accessing.message"), x.getStatus()); 
			}