AtomicProperties { public static AtomicProperties getInstance() throws IOException { if (ap == null) { ap = new AtomicProperties(); } return ap; } private  AtomicProperties(); double getVdWVolume(String symbol); double getNormalizedVdWVolume(String symbol); double getElectronegativity(String symbol); double getNormalizedElectronegativity(String symbol); double getPolarizability(String symbol); double getNormalizedPolarizability(String symbol); double getMass(String symbol); double getNormalizedMass(String symbol); static AtomicProperties getInstance();  }
@Test public void testGetInstance() throws IOException { AtomicProperties props = AtomicProperties.getInstance(); Assert.assertNotNull(props); AtomicProperties props2 = AtomicProperties.getInstance(); Assert.assertEquals(props2, props); }