collectionutils.java

JAVA 文章管理系统源码

        if(obj instanceof Map) {
            Map map = (Map)obj;
            if(map.containsKey(index)) {
                return map.get(index);
            }
        }
        int idx = -1;
        if(index instanceof Integer) {
            idx = ((Integer)index).intValue();
        }
        if(idx < 0) {
            return obj;
        } 
        else if(obj instanceof Map) {
            Map map = (Map)obj;
            Iterator iterator = map.keySet().iterator();
            return index(iterator, idx);
        } 
        else if(obj instanceof List) {
            return ((List)obj).get(idx);
        } 
        else if(obj instanceof Object[]) {
            return ((Object[])obj)[idx];
        } 
        else if(obj instanceof Enumeration) {
            Enumeration it = (Enumeration)obj;
            while(it.hasMoreElements()) {
                idx--;
                if(idx == -1) {
                    return it.nextElement();
                } else {
                    it.nextElement();
                }
            }
        } 
        else if(obj instanceof Iterator) {
            return index((Iterator)obj, idx);
        }
        else if(obj instanceof Collection) {
            Iterator iterator = ((Collection)obj).iterator();
            return index(iterator, idx);
        }
        return obj;
    }

    private static Object index(Iterator iterator, int idx) {
        while(iterator.hasNext()) {
            idx--;
            if(idx == -1) {
                return iterator.next();
            } else {
                iterator.next();
            }
        }
        return iterator;
    }
    
    /**
     * Returns the <code>index</code>-th value in <code>object</code>, throwing
     * <code>IndexOutOfBoundsException</code> if there is no such element or 
     * <code>IllegalArgumentException</code> if <code>object</code> is not an 
     * instance of one of the supported types.
     * <p>
     * The supported types, and associated semantics are:
     * <ul>
     * <li> Map -- the value returned is the <code>Map.Entry</code> in position 
     *      <code>index</code> in the map's <code>entrySet</code> iterator, 
     *      if there is such an entry.</li>
     * <li> List -- this method is equivalent to the list's get method.</li>
     * <li> Array -- the <code>index</code>-th array entry is returned, 
     *      if there is such an entry; otherwise an <code>IndexOutOfBoundsException</code>
     *      is thrown.</li>
     * <li> Collection -- the value returned is the <code>index</code>-th object 
     *      returned by the collection's default iterator, if there is such an element.</li>
     * <li> Iterator or Enumeration -- the value returned is the
     *      <code>index</code>-th object in the Iterator/Enumeration, if there
     *      is such an element.  The Iterator/Enumeration is advanced to 
     *      <code>index</code> (or to the end, if <code>index</code> exceeds the 
     *      number of entries) as a side effect of this method.</li>
     * </ul>
     * 
     * @param object  the object to get a value from
     * @param index  the index to get
     * @return the object at the specified index
     * @throws IndexOutOfBoundsException if the index is invalid
     * @throws IllegalArgumentException if the object type is invalid
     */
    public static Object get(Object object, int index) {
        if (index < 0) {
            throw new IndexOutOfBoundsException("Index cannot be negative: " + index);
        }
        if (object instanceof Map) {
            Map map = (Map) object;
            Iterator iterator = map.entrySet().iterator();
            return get(iterator, index);
        } else if (object instanceof List) {
            return ((List) object).get(index);
        } else if (object instanceof Object[]) {
            return ((Object[]) object)[index];
        } else if (object instanceof Iterator) {
            Iterator it = (Iterator) object;
            while (it.hasNext()) {
                index--;
                if (index == -1) {
                    return it.next();
                } else {
                    it.next();
                }
            }
            throw new IndexOutOfBoundsException("Entry does not exist: " + index);
        } else if (object instanceof Collection) {
            Iterator iterator = ((Collection) object).iterator();
            return get(iterator, index);
        } else if (object instanceof Enumeration) {
            Enumeration it = (Enumeration) object;
            while (it.hasMoreElements()) {
                index--;
                if (index == -1) {
                    return it.nextElement();
                } else {
                    it.nextElement();
                }
            }
            throw new IndexOutOfBoundsException("Entry does not exist: " + index);
        } else if (object == null) {
            throw new IllegalArgumentException("Unsupported object type: null");
        } else {
            try {
                return Array.get(object, index);
            } catch (IllegalArgumentException ex) {
                throw new IllegalArgumentException("Unsupported object type: " + object.getClass().getName());
            }
        }
    }
    
    /** 
     * Gets the size of the collection/iterator specified.
     * <p>
     * This method can handles objects as follows
     * <ul>
     * <li>Collection - the collection size
     * <li>Map - the map size
     * <li>Array - the array size
     * <li>Iterator - the number of elements remaining in the iterator
     * <li>Enumeration - the number of elements remaining in the enumeration
     * </ul>
     * 
     * @param object  the object to get the size of
     * @return the size of the specified collection
     * @throws IllegalArgumentException thrown if object is not recognised or null
     * @since Commons Collections 3.1
     */
    public static int size(Object object) {
        int total = 0;
        if (object instanceof Map) {
            total = ((Map) object).size();
        } else if (object instanceof Collection) {
            total = ((Collection) object).size();
        } else if (object instanceof Object[]) {
            total = ((Object[]) object).length;
        } else if (object instanceof Iterator) {
            Iterator it = (Iterator) object;
            while (it.hasNext()) {
                total++;
                it.next();
            }
        } else if (object instanceof Enumeration) {
            Enumeration it = (Enumeration) object;
            while (it.hasMoreElements()) {
                total++;
                it.nextElement();
            }
        } else if (object == null) {
            throw new IllegalArgumentException("Unsupported object type: null");
        } else {
            try {
                total = Array.getLength(object);
            } catch (IllegalArgumentException ex) {
                throw new IllegalArgumentException("Unsupported object type: " + object.getClass().getName());
            }
        }
        return total;
    }
    
    /**
     * Reverses the order of the given array.
     * 
     * @param array  the array to reverse
     */
    public static void reverseArray(Object[] array) {
        int i = 0;
        int j = array.length - 1;
        Object tmp;

        while (j > i) {
            tmp = array[j];
            array[j] = array[i];
            array[i] = tmp;
            j--;
            i++;
        }
    }

    private static final int getFreq(final Object obj, final Map freqMap) {
        Integer count = (Integer) freqMap.get(obj);
        if (count != null) {
            return count.intValue();
        }
        return 0;
    }

    /**
     * Returns true if no more elements can be added to the Collection.
     * <p>
     * This method uses the {@link BoundedCollection} interface to determine the
     * full status. If the collection does not implement this interface then
     * false is returned.
     * <p>
     * The collection does not have to implement this interface directly.
     * If the collection has been decorated using the decorators subpackage
     * then these will be removed to access the BoundedCollection.
     *
     * @param coll  the collection to check
     * @return true if the BoundedCollection is full
     * @throws NullPointerException if the collection is null
     */
    public static boolean isFull(Collection coll) {
        if (coll == null) {
            throw new NullPointerException("The collection must not be null");
        }
        if (coll instanceof BoundedCollection) {
            return ((BoundedCollection) coll).isFull();
        }
        try {
            BoundedCollection bcoll = UnmodifiableBoundedCollection.decorateUsing(coll);
            return bcoll.isFull();
            
        } catch (IllegalArgumentException ex) {
            return false;
        }
    }

    /**
     * Get the maximum number of elements that the Collection can contain.
     * <p>
     * This method uses the {@link BoundedCollection} interface to determine the
     * maximum size. If the collection does not implement this interface then
     * -1 is returned.
     * <p>
     * The collection does not have to implement this interface directly.
     * If the collection has been decorated using the decorators subpackage
     * then these will be removed to access the BoundedCollection.
     *
     * @param coll  the collection to check
     * @return the maximum size of the BoundedCollection, -1 if no maximum size
     * @throws NullPointerException if the collection is null
     */
    public static int maxSize(Collection coll) {
        if (coll == null) {
            throw new NullPointerException("The collection must not be null");
        }
        if (coll instanceof BoundedCollection) {
            return ((BoundedCollection) coll).maxSize();
        }
        try {
            BoundedCollection bcoll = UnmodifiableBoundedCollection.decorateUsing(coll);
            return bcoll.maxSize();
            
        } catch (IllegalArgumentException ex) {
            return -1;
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Returns a synchronized collection backed by the given collection.
     * <p>
     * You must manually synchronize on the returned buffer's iterator to 
     * avoid non-deterministic behavior:
     *  
     * <pre>
     * Collection c = CollectionUtils.synchronizedCollection(myCollection);
     * synchronized (c) {
     *     Iterator i = c.iterator();
     *     while (i.hasNext()) {
     *         process (i.next());
     *     }
     * }
     * </pre>
     * 
     * This method uses the implementation in the decorators subpackage.
     * 
     * @param collection  the collection to synchronize, must not be null
     * @return a synchronized collection backed by the given collection
     * @throws IllegalArgumentException  if the collection is null
     */
    public static Collection synchronizedCollection(Collection collection) {
        return SynchronizedCollection.decorate(collection);
    }

    /**
     * Returns an unmodifiable collection backed by the given collection.
     * <p>
     * This method uses the implementation in the decorators subpackage.
     *
     * @param collection  the collection to make unmodifiable, must not be null
     * @return an unmodifiable collection backed by the given collection
     * @throws IllegalArgumentException  if the collection is null
     */
    public static Collection unmodifiableCollection(Collection collection) {
        return UnmodifiableCollection.decorate(collection);
    }

    /**
     * Returns a predicated (validating) collection backed by the given collection.
     * <p>
     * Only objects that pass the test in the given predicate can be added to the collection.
     * Trying to add an invalid object results in an IllegalArgumentException.
     * It is important not to use the original collection after invoking this method,
     * as it is a backdoor for adding invalid objects.
     *
     * @param collection  the collection to predicate, must not be null
     * @param predicate  the predicate for the collection, must not be null
     * @return a predicated collection backed by the given collection
     * @throws IllegalArgumentException  if the Collection is null
     */
    public static Collection predicatedCollection(Collection collection, Predicate predicate) {
        return PredicatedCollection.decorate(collection, predicate);
    }

    /**
     * Returns a typed collection backed by the given collection.
     * <p>
     * Only objects of the specified type can be added to the collection.
     * 
     * @param collection  the collection to limit to a specific type, must not be null
     * @param type  the type of objects which may be added to the collection
     * @return a typed collection backed by the specified collection
     */
    public static Collection typedCollection(Collection collection, Class type) {
        return TypedCollection.decorate(collection, type);
    }
    
    /**
     * Returns a transformed bag backed by the given collection.
     * <p>
     * Each object is passed through the transformer as it is added to the
     * Collection. It is important not to use the original collection after invoking this 
     * method, as it is a backdoor for adding untransformed objects.
     *
     * @param collection  the collection to predicate, must not be null
     * @param transformer  the transformer for the collection, must not be null
     * @return a transformed collection backed by the given collection
     * @throws IllegalArgumentException  if the Collection or Transformer is null
     */
    public static Collection transformedCollection(Collection collection, Transformer transformer) {
        return TransformedCollection.decorate(collection, transformer);
    }
    
}