Here you can find the source of messageWarning(String s)
public static void messageWarning(String s)
//package com.java2s; /**/* w ww . j a v a 2 s . c om*/ * Copyright (c) 2001-2016 Mathew A. Nelson and Robocode contributors * All rights reserved. This program and the accompanying materials * are made available under the terms of the Eclipse Public License v1.0 * which accompanies this distribution, and is available at * http://robocode.sourceforge.net/license/epl-v10.html */ import javax.swing.*; public class Main { public static void messageWarning(String s) { JOptionPane.showMessageDialog(null, s, "Warning", JOptionPane.WARNING_MESSAGE); } }