IPreferenceStore preferenceStore= JavaPlugin.getDefault().getPreferenceStore();
LazyJavaCompletionProposal proposal;
if (preferenceStore.getBoolean(PreferenceConstants.CODEASSIST_GUESS_METHOD_ARGUMENTS))
proposal= new ParameterGuessingProposal(methodProposal, getCompilationUnit());
else
proposal= new ExperimentalProposal(methodProposal, getCompilationUnit());
return proposal;
}