code: // from gee.cs.oswego.edu/home/jsr166/jsr166
  
  package jsr166tests.tck;
  
  /*
   * Written by Doug Lea with assistance from members of JCP JSR-166
   * Expert Group and released to the public domain, as explained at
   * http://creativecommons.org/licenses/publicdomain
   * Other contributors include Andrew Wright, Jeffrey Hayes,
   * Pat Fisher, Mike Judd.
   */
  
  import junit.framework.*;
  
  public class SystemTest extends JSR166TestCase {
      public static void main(String[] args) {
          junit.textui.TestRunner.run(suite());
      }
  
      public static Test suite() {
          return new TestSuite(SystemTest.class);
      }
  
      /**
       * Worst case rounding for millisecs; set for 60 cycle millis clock.
       * This value might need to be changed on JVMs with coarser
       *  System.currentTimeMillis clocks.
       */
      static final long MILLIS_ROUND = 17;
  
      /**
       * Nanos between readings of millis is no longer than millis (plus
       * possible rounding).
       * This shows only that nano timing not (much) worse than milli.
       */
      public void testNanoTime1() throws InterruptedException {
          long m1 = System.currentTimeMillis();
          Thread.sleep(1);
          long n1 = System.nanoTime();
          Thread.sleep(SHORT_DELAY_MS);
          long n2 = System.nanoTime();
          Thread.sleep(1);
          long m2 = System.currentTimeMillis();
          long millis = m2 - m1;
          long nanos = n2 - n1;
          assertTrue(nanos >= 0);
          long nanosAsMillis = nanos / 1000000;
          assertTrue(nanosAsMillis <= millis + MILLIS_ROUND);
      }
  
      /**
       * Millis between readings of nanos is less than nanos, adjusting
       * for rounding.
       * This shows only that nano timing not (much) worse than milli.
       */
      public void testNanoTime2() throws InterruptedException {
          long n1 = System.nanoTime();
          Thread.sleep(1);
          long m1 = System.currentTimeMillis();
          Thread.sleep(SHORT_DELAY_MS);
          long m2 = System.currentTimeMillis();
          Thread.sleep(1);
          long n2 = System.nanoTime();
          long millis = m2 - m1;
          long nanos = n2 - n1;
  
          assertTrue(nanos >= 0);
          long nanosAsMillis = nanos / 1000000;
          assertTrue(millis <= nanosAsMillis + MILLIS_ROUND);
      }
  
  }
  