Here you can find the source of isGTKUI()
public static boolean isGTKUI()
//package com.java2s; /*//from w w w . j a va 2 s . c om * Copyright (c) 2006-2017 DMDirc Developers * * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated * documentation files (the "Software"), to deal in the Software without restriction, including without limitation the * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to * permit persons to whom the Software is furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in all copies or substantial portions of the * Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE * WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS * OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */ import javax.swing.UIManager; import javax.swing.UIManager.LookAndFeelInfo; public class Main { /** * GTK LAF class name. */ private static final String GTKUI = "com.sun.java.swing.plaf.gtk.GTKLookAndFeel"; /** * Check if we are using the GTK look and feel. * * @return true iif the LAF is GTK */ public static boolean isGTKUI() { return GTKUI.equals(UIManager.getLookAndFeel().getClass().getName()); } /** * Returns the class name of the look and feel from its display name. * * @param displayName Look and feel display name * * @return Look and feel class name or a zero length string */ public static String getLookAndFeel(final String displayName) { if (displayName == null || displayName.isEmpty() || "Native".equals(displayName)) { return UIManager.getSystemLookAndFeelClassName(); } final StringBuilder classNameBuilder = new StringBuilder(); for (LookAndFeelInfo laf : UIManager.getInstalledLookAndFeels()) { if (laf.getName().equals(displayName)) { classNameBuilder.append(laf.getClassName()); break; } } if (classNameBuilder.length() == 0) { classNameBuilder.append(UIManager.getSystemLookAndFeelClassName()); } return classNameBuilder.toString(); } }