collectionutils.java

JAVA 文章管理系统源码

    public static Object find(Collection collection, Predicate predicate) {
        if (collection != null && predicate != null) {
            for (Iterator iter = collection.iterator(); iter.hasNext();) {
                Object item = iter.next();
                if (predicate.evaluate(item)) {
                    return item;
                }
            }
        }
        return null;
    }
    
    /** 
     * Executes the given closure on each element in the collection.
     * <p>
     * If the input collection or closure is null, there is no change made.
     * 
     * @param collection  the collection to get the input from, may be null
     * @param closure  the closure to perform, may be null
     */
    public static void forAllDo(Collection collection, Closure closure) {
        if (collection != null && closure != null) {
            for (Iterator it = collection.iterator(); it.hasNext();) {
                closure.execute(it.next());
            }
        }
    }

    /** 
     * Filter the collection by applying a Predicate to each element. If the
     * predicate returns false, remove the element.
     * <p>
     * If the input collection or predicate is null, there is no change made.
     * 
     * @param collection  the collection to get the input from, may be null
     * @param predicate  the predicate to use as a filter, may be null
     */
    public static void filter(Collection collection, Predicate predicate) {
        if (collection != null && predicate != null) {
            for (Iterator it = collection.iterator(); it.hasNext();) {
                if (predicate.evaluate(it.next()) == false) {
                    it.remove();
                }
            }
        }
    }

    /** 
     * Transform the collection by applying a Transformer to each element.
     * <p>
     * If the input collection or transformer is null, there is no change made.
     * <p>
     * This routine is best for Lists, for which set() is used to do the 
     * transformations "in place."  For other Collections, clear() and addAll()
     * are used to replace elements.  
     * <p>
     * If the input collection controls its input, such as a Set, and the
     * Transformer creates duplicates (or are otherwise invalid), the 
     * collection may reduce in size due to calling this method.
     * 
     * @param collection  the collection to get the input from, may be null
     * @param transformer  the transformer to perform, may be null
     */
    public static void transform(Collection collection, Transformer transformer) {
        if (collection != null && transformer != null) {
            if (collection instanceof List) {
                List list = (List) collection;
                for (ListIterator it = list.listIterator(); it.hasNext();) {
                    it.set(transformer.transform(it.next()));
                }
            } else {
                Collection resultCollection = collect(collection, transformer);
                collection.clear();
                collection.addAll(resultCollection);
            }
        }
    }

    /** 
     * Counts the number of elements in the input collection that match the predicate.
     * <p>
     * A <code>null</code> collection or predicate matches no elements.
     * 
     * @param inputCollection  the collection to get the input from, may be null
     * @param predicate  the predicate to use, may be null
     * @return the number of matches for the predicate in the collection
     */
    public static int countMatches(Collection inputCollection, Predicate predicate) {
        int count = 0;
        if (inputCollection != null && predicate != null) {
            for (Iterator it = inputCollection.iterator(); it.hasNext();) {
                if (predicate.evaluate(it.next())) {
                    count++;
                }
            }
        }
        return count;
    }

    /** 
     * Answers true if a predicate is true for at least one element of a collection.
     * <p>
     * A <code>null</code> collection or predicate returns false.
     * 
     * @param collection the collection to get the input from, may be null
     * @param predicate the predicate to use, may be null
     * @return true if at least one element of the collection matches the predicate
     */
    public static boolean exists(Collection collection, Predicate predicate) {
        if (collection != null && predicate != null) {
            for (Iterator it = collection.iterator(); it.hasNext();) {
                if (predicate.evaluate(it.next())) {
                    return true;
                }
            }
        }
        return false;
    }

    /** 
     * Selects all elements from input collection which match the given predicate
     * into an output collection.
     * <p>
     * A <code>null</code> predicate matches no elements.
     * 
     * @param inputCollection  the collection to get the input from, may not be null
     * @param predicate  the predicate to use, may be null
     * @return the elements matching the predicate (new list)
     * @throws NullPointerException if the input collection is null
     */
    public static Collection select(Collection inputCollection, Predicate predicate) {
        ArrayList answer = new ArrayList(inputCollection.size());
        select(inputCollection, predicate, answer);
        return answer;
    }

    /** 
     * Selects all elements from input collection which match the given predicate
     * and adds them to outputCollection.
     * <p>
     * If the input collection or predicate is null, there is no change to the 
     * output collection.
     * 
     * @param inputCollection  the collection to get the input from, may be null
     * @param predicate  the predicate to use, may be null
     * @param outputCollection  the collection to output into, may not be null
     */
    public static void select(Collection inputCollection, Predicate predicate, Collection outputCollection) {
        if (inputCollection != null && predicate != null) {
            for (Iterator iter = inputCollection.iterator(); iter.hasNext();) {
                Object item = iter.next();
                if (predicate.evaluate(item)) {
                    outputCollection.add(item);
                }
            }
        }
    }
    
    /**
     * Selects all elements from inputCollection which don't match the given predicate
     * into an output collection.
     * <p>
     * If the input predicate is <code>null</code>, the result is an empty list.
     * 
     * @param inputCollection  the collection to get the input from, may not be null
     * @param predicate  the predicate to use, may be null
     * @return the elements <b>not</b> matching the predicate (new list)
     * @throws NullPointerException if the input collection is null
     */
    public static Collection selectRejected(Collection inputCollection, Predicate predicate) {
        ArrayList answer = new ArrayList(inputCollection.size());
        selectRejected(inputCollection, predicate, answer);
        return answer;
    }
    
    /** 
     * Selects all elements from inputCollection which don't match the given predicate
     * and adds them to outputCollection.
     * <p>
     * If the input predicate is <code>null</code>, no elements are added to <code>outputCollection</code>.
     * 
     * @param inputCollection  the collection to get the input from, may be null
     * @param predicate  the predicate to use, may be null
     * @param outputCollection  the collection to output into, may not be null
     */
    public static void selectRejected(Collection inputCollection, Predicate predicate, Collection outputCollection) {
        if (inputCollection != null && predicate != null) {
            for (Iterator iter = inputCollection.iterator(); iter.hasNext();) {
                Object item = iter.next();
                if (predicate.evaluate(item) == false) {
                    outputCollection.add(item);
                }
            }
        }
    }
    
    /** 
     * Returns a new Collection consisting of the elements of inputCollection transformed
     * by the given transformer.
     * <p>
     * If the input transformer is null, the result is an empty list.
     * 
     * @param inputCollection  the collection to get the input from, may not be null
     * @param transformer  the transformer to use, may be null
     * @return the transformed result (new list)
     * @throws NullPointerException if the input collection is null
     */
    public static Collection collect(Collection inputCollection, Transformer transformer) {
        ArrayList answer = new ArrayList(inputCollection.size());
        collect(inputCollection, transformer, answer);
        return answer;
    }
    
    /** 
     * Transforms all elements from the inputIterator with the given transformer 
     * and adds them to the outputCollection.
     * <p>
     * If the input iterator or transformer is null, the result is an empty list.
     * 
     * @param inputIterator  the iterator to get the input from, may be null
     * @param transformer  the transformer to use, may be null
     * @return the transformed result (new list)
     */
    public static Collection collect(Iterator inputIterator, Transformer transformer) {
        ArrayList answer = new ArrayList();
        collect(inputIterator, transformer, answer);
        return answer;
    }
    
    /** 
     * Transforms all elements from inputCollection with the given transformer 
     * and adds them to the outputCollection.
     * <p>
     * If the input collection or transformer is null, there is no change to the 
     * output collection.
     *
     * @param inputCollection  the collection to get the input from, may be null
     * @param transformer  the transformer to use, may be null
     * @param outputCollection  the collection to output into, may not be null
     * @return the outputCollection with the transformed input added
     * @throws NullPointerException if the output collection is null
     */
    public static Collection collect(Collection inputCollection, final Transformer transformer, final Collection outputCollection) {
        if (inputCollection != null) {
            return collect(inputCollection.iterator(), transformer, outputCollection);
        }
        return outputCollection;
    }

    /** 
     * Transforms all elements from the inputIterator with the given transformer 
     * and adds them to the outputCollection.
     * <p>
     * If the input iterator or transformer is null, there is no change to the 
     * output collection.
     *
     * @param inputIterator  the iterator to get the input from, may be null
     * @param transformer  the transformer to use, may be null
     * @param outputCollection  the collection to output into, may not be null
     * @return the outputCollection with the transformed input added
     * @throws NullPointerException if the output collection is null
     */
    public static Collection collect(Iterator inputIterator, final Transformer transformer, final Collection outputCollection) {
        if (inputIterator != null && transformer != null) {
            while (inputIterator.hasNext()) {
                Object item = inputIterator.next();
                Object value = transformer.transform(item);
                outputCollection.add(value);
            }
        }
        return outputCollection;
    }

    /**
     * Adds all elements in the iteration to the given collection.
     * 
     * @param collection  the collection to add to
     * @param iterator  the iterator of elements to add, may not be null
     * @throws NullPointerException if the collection or iterator is null
     */
    public static void addAll(Collection collection, Iterator iterator) {
        while (iterator.hasNext()) {
            collection.add(iterator.next());
        }
    }
    
    /**
     * Adds all elements in the enumeration to the given collection.
     * 
     * @param collection  the collection to add to
     * @param enumeration  the enumeration of elements to add, may not be null
     * @throws NullPointerException if the collection or enumeration is null
     */
    public static void addAll(Collection collection, Enumeration enumeration) {
        while (enumeration.hasMoreElements()) {
            collection.add(enumeration.nextElement());
        }
    }    
    
    /** 
     * Adds all elements in the array to the given collection.
     * 
     * @param collection  the collection to add to, may not be null
     * @param elements  the array of elements to add, may not be null
     * @throws NullPointerException if the collection or array is null
     */
    public static void addAll(Collection collection, Object[] elements) {
        for (int i = 0, size = elements.length; i < size; i++) {
            collection.add(elements[i]);
        }
    }    
    
    /**
     * Given an Object, and an index, returns the nth value in the
     * object.
     * <ul>
     * <li>If obj is a Map, returns the nth value from the <b>keySet</b> iterator, unless 
     *     the Map contains an Integer key with integer value = idx, in which case the
     *     corresponding map entry value is returned.  If idx exceeds the number of entries in
     *     the map, an empty Iterator is returned.
     * <li>If obj is a List or an array, returns the nth value, throwing IndexOutOfBoundsException,
     *     ArrayIndexOutOfBoundsException, resp. if the nth value does not exist.
     * <li>If obj is an iterator, enumeration or Collection, returns the nth value from the iterator,
     *     returning an empty Iterator (resp. Enumeration) if the nth value does not exist.
     * <li>Returns the original obj if it is null or not a Collection or Iterator.
     * </ul>
     * 
     * @param obj  the object to get an index of, may be null
     * @param idx  the index to get
     * @throws IndexOutOfBoundsException
     * @throws ArrayIndexOutOfBoundsException
     *
     * @deprecated use {@link #get(Object, int)} instead. Will be removed in v4.0
     */
    public static Object index(Object obj, int idx) {
        return index(obj, new Integer(idx));
    }
    
    /**
     * Given an Object, and a key (index), returns the value associated with
     * that key in the Object. The following checks are made:
     * <ul>
     * <li>If obj is a Map, use the index as a key to get a value. If no match continue.
     * <li>Check key is an Integer. If not, return the object passed in.
     * <li>If obj is a Map, get the nth value from the <b>keySet</b> iterator.
     *     If the Map has fewer than n entries, return an empty Iterator.
     * <li>If obj is a List or an array, get the nth value, throwing IndexOutOfBoundsException,
     *     ArrayIndexOutOfBoundsException, resp. if the nth value does not exist.
     * <li>If obj is an iterator, enumeration or Collection, get the nth value from the iterator,
     *     returning an empty Iterator (resp. Enumeration) if the nth value does not exist.
     * <li>Return the original obj.
     * </ul>
     * 
     * @param obj  the object to get an index of
     * @param index  the index to get
     * @return the object at the specified index
     * @throws IndexOutOfBoundsException
     * @throws ArrayIndexOutOfBoundsException
     *
     * @deprecated use {@link #get(Object, int)} instead. Will be removed in v4.0
     */
    public static Object index(Object obj, Object index) {