Here you can find the source of isMarker(JComponent component)
static boolean isMarker(JComponent component)
//package com.java2s; // Licensed under the Apache License, Version 2.0 (the "License"); import javax.swing.JComponent; import javax.swing.JLabel; public class Main { static final private String MARKER_NAME = "DesignGridLayout.spanRow-Marker"; static boolean isMarker(JComponent component) { return (component instanceof JLabel) && (MARKER_NAME.equals(component.getName())); }/*from w w w . j a v a 2 s .c om*/ }