MapConfiguration extends AbstractConfiguration { @Override public boolean containsKey(String key) { return (null == key) ? false : configMap.containsKey(key); } MapConfiguration();  MapConfiguration(Map<String, String> configMap);  MapConfiguration(Configuration config); @Override Configuration subset(String prefix); @Override Configuration strippedSubset(String prefix); static MapConfiguration merge(Configuration ... configs); @Override boolean isEmpty(); @Override boolean containsKey(String key); @Override void setProperty(String key, String value); @Override void clear(); @Override void clearProperty(String key); @Override Iterable<String> getKeys(); @Override String getProperty(String key); @Override String getProperty(String key, String defaultValue); @Override String toString();  }
@Test public void testContainsKey() { assertFalse(config.containsKey("x")); config.setProperty("x", "y"); assertTrue(config.containsKey("x")); }