Bug 41491 Add constructors from fields issues
200300813 a. add visibility buttons like 'Add constructor from super class'
org.eclipse.jdt.ui/ui/org/eclipse/jdt/ui/actions/GenerateNewConstructorUsingFieldsAction.java
public void selectionChanged(SelectionChangedEvent event) {
				IStructuredSelection selection= (IStructuredSelection) fTreeViewer.getSelection();
				List selectedList= selection.toList();
				GenerateConstructorUsingFieldsContentProvider cp= (GenerateConstructorUsingFieldsContentProvider) getContentProvider();
				fButtonControls[UP_INDEX].setEnabled(cp.canMoveUp(selectedList));
				fButtonControls[DOWN_INDEX].setEnabled(cp.canMoveDown(selectedList));
			}
			public void doubleClick(DoubleClickEvent event) {
				
			}
		}
		public IMethod[] getSuperConstructors() {
			return fSuperConstructors;
		}
		public void setOmitSuper(boolean omitSuper) {
			if (fOmitSuper != omitSuper)  {
				fOmitSuper= omitSuper;
				fGenConstructorSettings.put(OMIT_SUPER, omitSuper);
			}	
		}
		public boolean isOmitSuper() {
			return fOmitSuper;
		}
	}
	private static class GenerateConstructorUsingFieldsContentProvider implements ITreeContentProvider {