Here you can find the source of isKeySame(String key, Properties p1, Properties p2)
private static boolean isKeySame(String key, Properties p1, Properties p2)
//package com.java2s; /*//from w w w .ja v a 2 s .co m Copyright (c) 2000-2003 Board of Trustees of Leland Stanford Jr. University, all rights reserved. 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 STANFORD UNIVERSITY 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. Except as contained in this notice, the name of Stanford University shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization from Stanford University. */ import java.util.*; public class Main { private static final String noProp = new String(); private static boolean isKeySame(String key, Properties p1, Properties p2) { Object o1 = p1.getProperty(key); Object o2 = p2.getProperty(key, noProp); return (o1 == o2) || // o2 == noProp means p2 didn't have key that p1 has. // we know o1 != o2, so if o1 == null, o2 != null. !((o2 == noProp || o1 == null || !o1.equals(o2))); } }