Examples of java.util.HashSet

java.util.HashSet
This class implements the Set interface, backed by a hash table (actually a HashMap instance). It makes no guarantees as to the iteration order of the set; in particular, it does not guarantee that the order will remain constant over time. This class permits the null element.
This class offers constant time performance for the basic operations (add, remove, contains and size), assuming the hash function disperses the elements properly among the buckets. Iterating over this set requires time proportional to the sum of the HashSet instance's size (the number of elements) plus the "capacity" of the backing HashMap instance (the number of buckets). Thus, it's very important not to set the initial capacity too high (or the load factor too low) if iteration performance is important.
Note that this implementation is not synchronized. If multiple threads access a hash set concurrently, and at least one of the threads modifies the set, it must be synchronized externally. This is typically accomplished by synchronizing on some object that naturally encapsulates the set. If no such object exists, the set should be "wrapped" using the {@link Collections#synchronizedSet Collections.synchronizedSet}method. This is best done at creation time, to prevent accidental unsynchronized access to the set:
```
 Set s = Collections.synchronizedSet(new HashSet(...));
```
The iterators returned by this class's iterator method are fail-fast: if the set is modified at any time after the iterator is created, in any way except through the iterator's own remove method, the Iterator throws a {@link ConcurrentModificationException}. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.
Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.
This class is a member of the Java Collections Framework. @param < E> the type of elements maintained by this set @author Josh Bloch @author Neal Gafter @version 1.37, 04/21/06 @see Collection @see Set @see TreeSet @see HashMap @since 1.2

        }
        
        version = signerversion = 1;
        certs = new ArrayList();
        crls = new ArrayList();
        digestalgos = new HashSet();
        digestalgos.add(digestAlgorithm);
        
        //
        // Copy in the certificates and crls used to sign the private key.
        //

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    QueryResolver.resolveCommand(rsQuery, planEnv.getGlobalMetadata());
    }
    
    private static Collection getExternalGroups(MappingSourceNode sourceNode) {
        Collection externalGroups = new HashSet();


        MappingSourceNode parentSource = sourceNode.getParentSourceNode();
        while (parentSource != null) {
            externalGroups.add(new GroupSymbol(parentSource.getActualResultSetName()));
            parentSource = parentSource.getParentSourceNode();
        }
        return externalGroups;
    }

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        throws QueryResolverException,QueryMetadataException,TeiidComponentException {
        
        GroupSymbol oldGroupSymbol = new GroupSymbol(oldGroup);
        ResolverUtil.resolveGroup(oldGroupSymbol, metadata);
        
        HashSet projectedElements = new HashSet(ResolverUtil.resolveElementsInGroup(oldGroupSymbol, metadata));
        
        symbolMap.putAll(QueryUtil.createSymbolMap(oldGroupSymbol, newGroup, projectedElements));
    }

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     */
    private static Set collectSourceNodesInConjunct(Criteria conjunct, MappingNode context, MappingDocument mappingDoc)
        throws QueryPlannerException {
        
        Collection elements = ElementCollectorVisitor.getElements(conjunct, true);
        Set resultSets = new HashSet();
        
        String contextFullName = context.getFullyQualifiedName().toUpperCase();
        
        //validate that each element's group is under the current context or is in the direct parentage
        for (Iterator i = elements.iterator(); i.hasNext();) {
            ElementSymbol elementSymbol = (ElementSymbol)i.next();
            
            String elementFullName = elementSymbol.getCanonicalName();
            
            MappingNode node = MappingNode.findNode(mappingDoc, elementFullName);
            
            MappingNode elementRsNode = node.getSourceNode(); 
            if (elementRsNode == null) {
                throw new QueryPlannerException(QueryPlugin.Util.getString("CriteriaPlanner.invalid_element", elementSymbol)); //$NON-NLS-1$
            }
            
            String elementRsFullName = elementRsNode.getFullyQualifiedName().toUpperCase();
            
            //check for a match at or below the context
            if (contextFullName.equals(elementRsFullName) || 
                            elementRsFullName.startsWith(contextFullName + ElementSymbol.SEPARATOR)) {
                resultSets.add(elementRsNode);
                continue;
            }
            
            //check for match above the context
            if (contextFullName.startsWith(elementRsFullName + ElementSymbol.SEPARATOR)) {

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        if (context instanceof MappingSourceNode) {
            return (MappingSourceNode)context;
        }


        Set criteriaResultSets = new HashSet();
        // if the context node is not the root node then we need to find the root source node from list.
        for (Iterator i = resultSets.iterator(); i.hasNext();) {


            // these are actually source nodes.
            MappingNode node = (MappingNode)i.next();
   
            MappingNode root = node;
            
            while (node != null) {
                if (node instanceof MappingSourceNode) {
                    root = node;
                }
                node = node.getParent();
            }
            criteriaResultSets.add(root);
        }
   
        if (criteriaResultSets.size() != 1) {
            //TODO: this assumption could be relaxed if we allow context to be from a document perspective, rather than from a result set
            throw new QueryPlannerException(QueryPlugin.Util.getString("CriteriaPlanner.no_context", criteria)); //$NON-NLS-1$
        }
        return (MappingSourceNode)criteriaResultSets.iterator().next();
    }

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    /**
     * Test for duplicates when generating a bunch of IDs.
     */
    private static void helpTestDuplicates( int nGen ) {
        UUID uuid = null;
        Set uuids = new HashSet();
//        Set duplicates = new HashSet();


        // First test some fairly "regular" numbers...
        for ( int j = 0; j < Math.min(nGen,63); j++ ) {
            long v1 = 1L << j;
            long v2 = (1L << j)/2;
            uuid = new UUID(v1,v2);
            assertTrue( "UUID '" + uuid + "' is a duplicate!", !uuids.contains(uuid) ); //$NON-NLS-1$ //$NON-NLS-2$
            uuids.add(uuid);
        }


        // Then test some random numbers...
        java.util.Random rng = new java.util.Random();
        for ( int k = 0; k < nGen; k++ ) {
            long v1 = rng.nextLong();
            long v2 = rng.nextLong();
            uuid = new UUID(v1,v2);
            if ( uuids.contains(uuid) ) {
                fail( "UUID '" + uuid + "' is a duplicate!" ); //$NON-NLS-1$ //$NON-NLS-2$
            }
            uuids.add(uuid);
        }
    }

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        Set atomicQueries = TestOptimizer.getAtomicQueries(plan);
        assertEquals("Expected 2 queries to get pushed down", 2, atomicQueries.size()); //$NON-NLS-1$
        
        String expectedSql = "SELECT BQT1.SmallA.StringKey, BQT1.SmallA.IntKey FROM BQT1.SmallA"; //$NON-NLS-1$
        String expectedSql2 = "SELECT BQT1.SmallB.IntKey FROM BQT1.SmallB"; //$NON-NLS-1$
        Set expectedQueries = new HashSet();
        expectedQueries.add(expectedSql);
        expectedQueries.add(expectedSql2);
        assertEquals(expectedQueries, atomicQueries); 


        List[] input1 = new List[] { 
                                    Arrays.asList(new Object[] { "5", new Integer(5)}), //$NON-NLS-1$ 
                                };

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        assertEquals("Expected 2 queries to get pushed down", 2, atomicQueries.size()); //$NON-NLS-1$
        
        String expectedSql = "SELECT BQT1.SmallA.IntKey FROM BQT1.SmallA, BQT1.SmallB WHERE (BQT1.SmallA.IntKey = BQT1.SmallB.IntKey) AND (BQT1.SmallA.IntKey = 5) AND (BQT1.SmallB.IntKey = 5)"; //$NON-NLS-1$
        String expectedSql2 = "SELECT BQT2.SmallA.IntKey FROM BQT2.SmallA WHERE BQT2.SmallA.IntKey = 5"; //$NON-NLS-1$
        
        Set expectedQueries = new HashSet();
        expectedQueries.add(expectedSql);
        expectedQueries.add(expectedSql2);
        assertEquals(expectedQueries, atomicQueries); 


        List[] input1 = new List[] { 
                                      Arrays.asList(new Object[] { new Integer(5), new Integer(5)}), 
                                  };

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    /**
     * Load the stringified UUIDs from a file and test 'stringToObject'.
     */
    public static Collection helpTestStringToObject( String filename, boolean checkForDuplicates ) throws Exception {
        String stringifiedID = null;
        final Set objectIDs = new HashSet();
        try {
            Collection stringifiedIDs = helpLoad(filename);
            if ( DEBUG_PRINT ) {
                System.out.println("# of ids = " + stringifiedIDs.size() ); //$NON-NLS-1$
            }
            final Iterator iter = stringifiedIDs.iterator();
            while (iter.hasNext()) {
                stringifiedID = (String) iter.next();
                final ObjectID objectId = IDGenerator.getInstance().stringToObject(stringifiedID);
                if ( checkForDuplicates && objectIDs.contains(objectId) ) {
                    fail( "ObjectID '" + objectId + "' is a duplicate!" ); //$NON-NLS-1$ //$NON-NLS-2$
                }
                objectIDs.add(objectId);
            }


        } catch ( InvalidIDException e ) {
            fail("Unable to convert stringified ID \"" + stringifiedID + "\" to an ObjectID"); //$NON-NLS-1$ //$NON-NLS-2$
        }

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    /**
     * Test for duplicates when generating a bunch of IDs.
     */
    private void helpTestDuplicates( int nGen ) {
        UUID uuid = null;
        Set uuids = new HashSet();
//        Set duplicates = new HashSet();


        // Then test some random numbers...
//        java.util.Random rng = new java.util.Random();
        for ( int k = 0; k < nGen; k++ ) {
            uuid = (UUID)generator.create();
            assertTrue( "UUID '" + uuid + "' is a duplicate!", !uuids.contains(uuid) ); //$NON-NLS-1$ //$NON-NLS-2$
            uuids.add(uuid);
        }
    }

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