collection.java

这个是perst-269.zip下面的SOURCECODE,和大家分享了。

package org.garret.perst;

/**
 * The root interface in the <i>collection hierarchy</i>.  A collection
 * represents a group of objects, known as its <i>elements</i>.  Some
 * collections allow duplicate elements and others do not.  Some are ordered
 * and others unordered.  The SDK does not provide any <i>direct</i>
 * implementations of this interface: it provides implementations of more
 * specific subinterfaces like <tt>Set</tt> and <tt>List</tt>.  This interface
 * is typically used to pass collections around and manipulate them where
 * maximum generality is desired.
 *
 * <p><i>Bags</i> or <i>multisets</i> (unordered collections that may contain
 * duplicate elements) should implement this interface directly.
 *
 * <p>All general-purpose <tt>Collection</tt> implementation classes (which
 * typically implement <tt>Collection</tt> indirectly through one of its
 * subinterfaces) should provide two "standard" constructors: a void (no
 * arguments) constructor, which creates an empty collection, and a
 * constructor with a single argument of type <tt>Collection</tt>, which
 * creates a new collection with the same elements as its argument.  In
 * effect, the latter constructor allows the user to copy any collection,
 * producing an equivalent collection of the desired implementation type.
 * There is no way to enforce this convention (as interfaces cannot contain
 * constructors) but all of the general-purpose <tt>Collection</tt>
 * implementations in the Java platform libraries comply.
 *
 * <p>The "destructive" methods contained in this interface, that is, the
 * methods that modify the collection on which they operate, are specified to
 * throw <tt>UnsupportedOperationException</tt> if this collection does not
 * support the operation.  If this is the case, these methods may, but are not
 * required to, throw an <tt>UnsupportedOperationException</tt> if the
 * invocation would have no effect on the collection.  For example, invoking
 * the {@link #addAll(Collection)} method on an unmodifiable collection may,
 * but is not required to, throw the exception if the collection to be added
 * is empty.
 *
 * <p>Some collection implementations have restrictions on the elements that
 * they may contain.  For example, some implementations prohibit null elements,
 * and some have restrictions on the types of their elements.  Attempting to
 * add an ineligible element throws an unchecked exception, typically
 * <tt>NullPointerException</tt> or <tt>ClassCastException</tt>.  Attempting
 * to query the presence of an ineligible element may throw an exception,
 * or it may simply return false; some implementations will exhibit the former
 * behavior and some will exhibit the latter.  More generally, attempting an
 * operation on an ineligible element whose completion would not result in
 * the insertion of an ineligible element into the collection may throw an
 * exception or it may succeed, at the option of the implementation.
 * Such exceptions are marked as "optional" in the specification for this
 * interface. 
 */

public interface Collection {
    // Query Operations

    /**
     * Returns the number of elements in this collection.  If this collection
     * contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
     * <tt>Integer.MAX_VALUE</tt>.
     * 
     * @return the number of elements in this collection
     */
    int size();

    /**
     * Returns <tt>true</tt> if this collection contains no elements.
     *
     * @return <tt>true</tt> if this collection contains no elements
     */
    boolean isEmpty();

    /**
     * Returns <tt>true</tt> if this collection contains the specified
     * element.  More formally, returns <tt>true</tt> if and only if this
     * collection contains at least one element <tt>e</tt> such that
     * <tt>(o==null ? e==null : o.equals(e))</tt>.
     *
     * @param o element whose presence in this collection is to be tested.
     * @return <tt>true</tt> if this collection contains the specified
     *         element
     * @throws ClassCastException if the type of the specified element
     * 	       is incompatible with this collection (optional).
     * @throws NullPointerException if the specified element is null and this
     *         collection does not support null elements (optional).
     */
    boolean contains(Object o);

    /**
     * Returns an iterator over the elements in this collection.  There are no
     * guarantees concerning the order in which the elements are returned
     * (unless this collection is an instance of some class that provides a
     * guarantee).
     * 
     * @return an <tt>Iterator</tt> over the elements in this collection
     */
    Iterator iterator();

    /**
     * Returns an array containing all of the elements in this collection.  If
     * the collection makes any guarantees as to what order its elements are
     * returned by its iterator, this method must return the elements in the
     * same order.<p>
     *
     * The returned array will be "safe" in that no references to it are
     * maintained by this collection.  (In other words, this method must
     * allocate a new array even if this collection is backed by an array).
     * The caller is thus free to modify the returned array.<p>
     *
     * This method acts as bridge between array-based and collection-based
     * APIs.
     *
     * @return an array containing all of the elements in this collection
     */
    Object[] toArray();

    /**
     * Returns an array containing all of the elements in this collection; 
     * the runtime type of the returned array is that of the specified array.  
     * If the collection fits in the specified array, it is returned therein.  
     * Otherwise, a new array is allocated with the runtime type of the 
     * specified array and the size of this collection.<p>
     *
     * If this collection fits in the specified array with room to spare
     * (i.e., the array has more elements than this collection), the element
     * in the array immediately following the end of the collection is set to
     * <tt>null</tt>.  This is useful in determining the length of this
     * collection <i>only</i> if the caller knows that this collection does
     * not contain any <tt>null</tt> elements.)<p>
     *
     * If this collection makes any guarantees as to what order its elements
     * are returned by its iterator, this method must return the elements in
     * the same order.<p>
     *
     * Like the <tt>toArray</tt> method, this method acts as bridge between
     * array-based and collection-based APIs.  Further, this method allows
     * precise control over the runtime type of the output array, and may,
     * under certain circumstances, be used to save allocation costs<p>
     *
     * Suppose <tt>l</tt> is a <tt>List</tt> known to contain only strings.
     * The following code can be used to dump the list into a newly allocated
     * array of <tt>String</tt>:
     *
     * <pre>
     *     String[] x = (String[]) v.toArray(new String[0]);
     * </pre><p>
     *
     * Note that <tt>toArray(new Object[0])</tt> is identical in function to
     * <tt>toArray()</tt>.
     *
     * @param a the array into which the elements of this collection are to be
     *        stored, if it is big enough; otherwise, a new array of the same
     *        runtime type is allocated for this purpose.
     * @return an array containing the elements of this collection
     * 
     * @throws ArrayStoreException the runtime type of the specified array is
     *         not a supertype of the runtime type of every element in this
     *         collection.
     * @throws NullPointerException if the specified array is <tt>null</tt>.
     */
    
    Object[] toArray(Object a[]);

    // Modification Operations

    /**
     * Ensures that this collection contains the specified element (optional
     * operation).  Returns <tt>true</tt> if this collection changed as a
     * result of the call.  (Returns <tt>false</tt> if this collection does
     * not permit duplicates and already contains the specified element.)<p>
     *
     * Collections that support this operation may place limitations on what
     * elements may be added to this collection.  In particular, some
     * collections will refuse to add <tt>null</tt> elements, and others will
     * impose restrictions on the type of elements that may be added.
     * Collection classes should clearly specify in their documentation any
     * restrictions on what elements may be added.<p>
     *
     * If a collection refuses to add a particular element for any reason
     * other than that it already contains the element, it <i>must</i> throw
     * an exception (rather than returning <tt>false</tt>).  This preserves
     * the invariant that a collection always contains the specified element
     * after this call returns.
     *
     * @param o element whose presence in this collection is to be ensured.
     * @return <tt>true</tt> if this collection changed as a result of the
     *         call
     * 
     * @throws UnsupportedOperationException <tt>add</tt> is not supported by
     *         this collection.
     * @throws ClassCastException class of the specified element prevents it
     *         from being added to this collection.
     * @throws NullPointerException if the specified element is null and this
     *         collection does not support null elements.