Examples of java.util.Random

java.util.Random
An instance of this class is used to generate a stream of pseudorandom numbers. The class uses a 48-bit seed, which is modified using a linear congruential formula. (See Donald Knuth, The Art of Computer Programming, Volume 3, Section 3.2.1.)
If two instances of {@code Random} are created with the sameseed, and the same sequence of method calls is made for each, they will generate and return identical sequences of numbers. In order to guarantee this property, particular algorithms are specified for the class {@code Random}. Java implementations must use all the algorithms shown here for the class {@code Random}, for the sake of absolute portability of Java code. However, subclasses of class {@code Random}are permitted to use other algorithms, so long as they adhere to the general contracts for all the methods.
The algorithms implemented by class {@code Random} use a{@code protected} utility method that on each invocation can supplyup to 32 pseudorandomly generated bits.
Many applications will find the method {@link Math#random} simpler to use. @author Frank Yellin @version 1.47, 02/07/06 @since 1.0

{
   public void testArrayRepl() throws CloneNotSupportedException
   {
      int streamsize = 11000;
      byte[] b = new byte[streamsize];
      new Random().nextBytes(b);
      Cache<String, byte[]> cache1 = null, cache2 = null;


      try
      {
         Configuration c = new Configuration();

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   protected void threadSafetyTest(final boolean singleFqn) throws Exception
   {
      final CountDownLatch latch = new CountDownLatch(1);
      final Fqn fqn = Fqn.fromString("/a/b/c");
      final List<Fqn> fqns = new ArrayList<Fqn>(30);
      final Random r = new Random();
      if (!singleFqn)
      {
         for (int i = 0; i < 30; i++)
         {
            Fqn f = Fqn.fromString("/a/b/c/" + i);
            fqns.add(f);
            cache2.put(f, "k", "v");
            cache1.evict(f);
         }
      }
      else
      {
         cache2.put(fqn, "k", "v");
         cache1.evict(fqn);
      }
      final int loops = 25; // was 300
      final Set<Exception> exceptions = new CopyOnWriteArraySet<Exception>();


      Thread evictor = new Thread("Evictor")
      {
         public void run()
         {
            try
            {
               latch.await();
               for (int i = 0; i < loops; i++)
               {
                  Fqn f = singleFqn ? fqn : fqns.get(r.nextInt(fqns.size()));
                  cache1.evict(f);
                  TestingUtil.sleepRandom(50);
               }
            }
            catch (TimeoutException te)
            {
               // doesn't matter if we hit these on occasion
            }
            catch (Exception e)
            {
               exceptions.add(e);
            }
         }
      };


      evictor.start();


      Thread writer = new Thread("Writer")
      {
         public void run()
         {
            try
            {
               latch.await();
               for (int i = 0; i < loops; i++)
               {
                  Fqn f = singleFqn ? fqn : fqns.get(r.nextInt(fqns.size()));
                  cache2.put(f, "k", "v");
                  TestingUtil.sleepRandom(50);
               }
            }
            catch (Exception e)
            {
               exceptions.add(e);
            }
         }
      };


      writer.start();




      Thread reader1 = new Thread("Reader-1")
      {
         public void run()
         {
            try
            {
               latch.await();
               for (int i = 0; i < loops; i++)
               {
                  loader1.get(singleFqn ? fqn : fqns.get(r.nextInt(fqns.size())));
                  TestingUtil.sleepRandom(50);
               }
            }
            catch (Exception e)
            {
               exceptions.add(e);
            }
         }
      };
      reader1.start();


      Thread reader2 = new Thread("Reader-2")
      {
         public void run()
         {
            try
            {
               latch.await();
               for (int i = 0; i < loops; i++)
               {
                  loader1.getChildrenNames(singleFqn ? fqn.getParent() : fqns.get(r.nextInt(fqns.size())).getParent());
                  TestingUtil.sleepRandom(50);
               }
            }
            catch (Exception e)
            {
               exceptions.add(e);
            }
         }
      };
      reader2.start();


      Thread reader3 = new Thread("Reader-3")
      {
         public void run()
         {
            try
            {
               latch.await();
               for (int i = 0; i < loops; i++)
               {
                  loader1.getChildrenNames(singleFqn ? fqn : fqns.get(r.nextInt(fqns.size())));
                  TestingUtil.sleepRandom(50);
               }
            }
            catch (Exception e)
            {

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   protected void threadSafetyTest(final boolean singleFqn) throws Exception
   {
      final CountDownLatch latch = new CountDownLatch(1);
      final Fqn fqn = Fqn.fromString("/a/b/c");
      final List<Fqn> fqns = new ArrayList<Fqn>(30);
      final Random r = new Random();
      if (!singleFqn)
      {
         for (int i = 0; i < 30; i++)
         {
            Fqn f = Fqn.fromString("/a/b/c/" + i);
            fqns.add(f);
            loader.put(f, "k", "v");
         }
      }
      else
      {
         loader.put(fqn, "k", "v");
      }
      final int loops = 100;
      final Set<Exception> exceptions = new CopyOnWriteArraySet<Exception>();


      Thread remover1 = new Thread("Remover-1")
      {
         public void run()
         {
            try
            {
               latch.await();
               for (int i = 0; i < loops; i++)
               {
                  loader.remove(singleFqn ? fqn : fqns.get(r.nextInt(fqns.size())));
               }
            }
            catch (Exception e)
            {
               exceptions.add(e);
            }
         }
      };


      remover1.start();


      Thread remover2 = new Thread("Remover-2")
      {
         public void run()
         {
            try
            {
               latch.await();
               for (int i = 0; i < loops; i++)
               {
                  loader.remove(singleFqn ? fqn : fqns.get(r.nextInt(fqns.size())), "k");
               }
            }
            catch (Exception e)
            {
               exceptions.add(e);
            }
         }
      };


      remover2.start();




      Thread reader1 = new Thread("Reader-1")
      {
         public void run()
         {
            try
            {
               latch.await();
               for (int i = 0; i < loops; i++)
               {
                  loader.get(singleFqn ? fqn : fqns.get(r.nextInt(fqns.size())));
               }
            }
            catch (Exception e)
            {
               exceptions.add(e);
            }
         }
      };
      reader1.start();


      Thread reader2 = new Thread("Reader-2")
      {
         public void run()
         {
            try
            {
               latch.await();
               for (int i = 0; i < loops; i++)
               {
                  loader.getChildrenNames(singleFqn ? fqn : fqns.get(r.nextInt(fqns.size())));
               }
            }
            catch (Exception e)
            {
               exceptions.add(e);
            }
         }
      };
      reader2.start();




      Thread writer1 = new Thread("Writer-1")
      {
         public void run()
         {
            try
            {
               latch.await();
               for (int i = 0; i < loops; i++)
               {
                  loader.put(singleFqn ? fqn : fqns.get(r.nextInt(fqns.size())), "k", "v");
               }
            }
            catch (Exception e)
            {
               exceptions.add(e);
            }
         }
      };
      writer1.start();


      Thread writer2 = new Thread("Writer-2")
      {
         public void run()
         {
            try
            {
               latch.await();
               for (int i = 0; i < loops; i++)
               {
                  loader.put(singleFqn ? fqn : fqns.get(r.nextInt(fqns.size())), new HashMap<Object, Object>());
               }
            }
            catch (Exception e)
            {
               exceptions.add(e);

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        test(false, len);
        test(true, len);
    }


    private static void test(boolean fast, int len) {
        Random random = new Random(10);
        long time = System.currentTimeMillis();
        byte[] bin = new byte[len];
        random.nextBytes(bin);
        for (int i = 0; i < len; i++) {
            byte[] dec;
            if (fast) {
                byte[] enc = encodeFast(bin);
                dec = decodeFast(enc);

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  protected Destination getDestination() {
    if ((cluster != null) && ! cluster.isEmpty()) {
      Destination dest = null;
      String location = System.getProperty("location");
      if (location == null || location.equals("")) {
        int idx = new Random().nextInt(cluster.size());


        Object key[] = cluster.keySet().toArray();
        location = (String) key[idx];
        System.setProperty("location", location);
      }

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        }
    }


    public Random getRandom() {
        if (random == null) {
            random = new Random();
        }
        return random;
    }

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  protected ConnectionFactory getConnectionFactory() {
    if ((cluster != null) && ! cluster.isEmpty()) {
      ConnectionFactory cf = null;
      String location = System.getProperty("location");
      if (location == null || location.equals("")) {
        int idx = new Random().nextInt(cluster.size());


        Object key[] = cluster.keySet().toArray();
        location = (String) key[idx];
        System.setProperty("location", location);
      }

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        prep.setInt(1, 2);
        prep.setString(2, "face");
        prep.setString(3, "face");
        prep.execute();


        Random random = new Random(1);
        prep.setInt(1, 3);
        byte[] large = new byte[getSize(10 * 1024, 100 * 1024)];
        random.nextBytes(large);
        prep.setBytes(2, large);
        String largeText = new String(large, "ISO-8859-1");
        prep.setString(3, largeText);
        prep.execute();

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        test.test();
        test.test();
    }


    public void test() throws SQLException {
        Random random = new Random();
        for (int i = 0; i < getSize(1, 4); i++) {
            testAddDelete();
            int seed = random.nextInt();
            testCase(seed);
        }
    }

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    private void testOne(int seed) throws SQLException {
        org.h2.Driver.load();
        deleteDb("index");
        printTime("testIndex " + seed);
        Random random = new Random(seed);
        int distinct, prefixLength;
        if (random.nextBoolean()) {
            distinct = random.nextInt(8000) + 1;
            prefixLength = random.nextInt(8000) + 1;
        } else if (random.nextBoolean()) {
            distinct = random.nextInt(16000) + 1;
            prefixLength = random.nextInt(100) + 1;
        } else {
            distinct = random.nextInt(10) + 1;
            prefixLength = random.nextInt(10) + 1;
        }
        boolean delete = random.nextBoolean();
        StringBuilder buff = new StringBuilder();
        for (int j = 0; j < prefixLength; j++) {
            buff.append("x");
            if (buff.length() % 10 == 0) {
                buff.append(buff.length());
            }
        }
        String prefix = buff.toString().substring(0, prefixLength);
        DeleteDbFiles.execute(getBaseDir() + "/index", null, true);
        Connection conn = getConnection("index");
        try {
            Statement stat = conn.createStatement();
            stat.execute("CREATE TABLE a(text VARCHAR PRIMARY KEY)");
            PreparedStatement prepInsert = conn.prepareStatement("INSERT INTO a VALUES(?)");
            PreparedStatement prepDelete = conn.prepareStatement("DELETE FROM a WHERE text=?");
            PreparedStatement prepDeleteAllButOne = conn.prepareStatement("DELETE FROM a WHERE text <> ?");
            int count = 0;
            for (int i = 0; i < 1000; i++) {
                int y = random.nextInt(distinct);
                try {
                    prepInsert.setString(1, prefix + y);
                    prepInsert.executeUpdate();
                    count++;
                } catch (SQLException e) {
                    if (e.getSQLState().equals("23505")) {
                        // ignore
                    } else {
                        TestBase.logError("error", e);
                        break;
                    }
                }
                if (delete && random.nextInt(10) == 1) {
                    if (random.nextInt(4) == 1) {
                        try {
                            prepDeleteAllButOne.setString(1, prefix + y);
                            int deleted = prepDeleteAllButOne.executeUpdate();
                            if (deleted < count - 1) {
                                printError(seed, "deleted:" + deleted + " i:" + i);

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