abstractlist.java

java源代码 请看看啊 提点宝贵的意见

/*
 * @(#)AbstractList.java	1.37 03/01/18
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.util;

/**
 * This class provides a skeletal implementation of the <tt>List</tt>
 * interface to minimize the effort required to implement this interface
 * backed by a "random access" data store (such as an array).  For sequential
 * access data (such as a linked list), <tt>AbstractSequentialList</tt> should
 * be used in preference to this class.<p>
 *
 * To implement an unmodifiable list, the programmer needs only to extend this
 * class and provide implementations for the <tt>get(int index)</tt> and
 * <tt>size()</tt> methods.<p>
 *
 * To implement a modifiable list, the programmer must additionally override
 * the <tt>set(int index, Object element)</tt> method (which otherwise throws
 * an <tt>UnsupportedOperationException</tt>.  If the list is variable-size
 * the programmer must additionally override the <tt>add(int index, Object
 * element)</tt> and <tt>remove(int index)</tt> methods.<p>
 *
 * The programmer should generally provide a void (no argument) and collection
 * constructor, as per the recommendation in the <tt>Collection</tt> interface
 * specification.<p>
 *
 * Unlike the other abstract collection implementations, the programmer does
 * <i>not</i> have to provide an iterator implementation; the iterator and
 * list iterator are implemented by this class, on top the "random access"
 * methods: <tt>get(int index)</tt>, <tt>set(int index, Object element)</tt>,
 * <tt>set(int index, Object element)</tt>, <tt>add(int index, Object
 * element)</tt> and <tt>remove(int index)</tt>.<p>
 *
 * The documentation for each non-abstract methods in this class describes its
 * implementation in detail.  Each of these methods may be overridden if the
 * collection being implemented admits a more efficient implementation.<p>
 *
 * This class is a member of the 
 * <a href="{@docRoot}/../guide/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @author  Josh Bloch
 * @version 1.37, 01/18/03
 * @see Collection
 * @see List
 * @see AbstractSequentialList
 * @see AbstractCollection
 * @since 1.2
 */

public abstract class AbstractList extends AbstractCollection implements List {
    /**
     * Sole constructor.  (For invocation by subclass constructors, typically
     * implicit.)
     */
    protected AbstractList() {
    }

    /**
     * Appends the specified element to the end of this List (optional
     * operation). <p>
     *
     * This implementation calls <tt>add(size(), o)</tt>.<p>
     *
     * Note that this implementation throws an
     * <tt>UnsupportedOperationException</tt> unless <tt>add(int, Object)</tt>
     * is overridden.
     *
     * @param o element to be appended to this list.
     * 
     * @return <tt>true</tt> (as per the general contract of
     * <tt>Collection.add</tt>).
     * 
     * @throws UnsupportedOperationException if the <tt>add</tt> method is not
     * 		  supported by this Set.
     * 
     * @throws ClassCastException if the class of the specified element
     * 		  prevents it from being added to this set.
     * 
     * @throws IllegalArgumentException some aspect of this element prevents
     *            it from being added to this collection.
     */
    public boolean add(Object o) {
	add(size(), o);
	return true;
    }

    /**
     * Returns the element at the specified position in this list.
     *
     * @param index index of element to return.
     * 
     * @return the element at the specified position in this list.
     * @throws IndexOutOfBoundsException if the given index is out of range
     * 		  (<tt>index &lt; 0 || index &gt;= size()</tt>).
     */
    abstract public Object get(int index);

    /**
     * Replaces the element at the specified position in this list with the
     * specified element (optional operation). <p>
     *
     * This implementation always throws an
     * <tt>UnsupportedOperationException</tt>.
     *
     * @param index index of element to replace.
     * @param element element to be stored at the specified position.
     * @return the element previously at the specified position.
     * 
     * @throws UnsupportedOperationException if the <tt>set</tt> method is not
     *		  supported by this List.
     * @throws ClassCastException if the class of the specified element
     * 		  prevents it from being added to this list.
     * @throws IllegalArgumentException if some aspect of the specified
     *		  element prevents it from being added to this list.
     * 
     * @throws IndexOutOfBoundsException if the specified index is out of
     *            range (<tt>index &lt; 0 || index &gt;= size()</tt>).
     */
    
    public Object set(int index, Object element) {
	throw new UnsupportedOperationException();
    }

    /**
     * Inserts the specified element at the specified position in this list
     * (optional operation).  Shifts the element currently at that position
     * (if any) and any subsequent elements to the right (adds one to their
     * indices).<p>
     *
     * This implementation always throws an UnsupportedOperationException.
     *
     * @param index index at which the specified element is to be inserted.
     * @param element element to be inserted.
     * 
     * @throws UnsupportedOperationException if the <tt>add</tt> method is not
     *		  supported by this list.
     * @throws ClassCastException if the class of the specified element
     * 		  prevents it from being added to this list.
     * @throws IllegalArgumentException if some aspect of the specified
     *		  element prevents it from being added to this list.
     * @throws IndexOutOfBoundsException index is out of range (<tt>index &lt;
     *		  0 || index &gt; size()</tt>).
     */
    public void add(int index, Object element) {
	throw new UnsupportedOperationException();
    }

    /**
     * Removes the element at the specified position in this list (optional
     * operation).  Shifts any subsequent elements to the left (subtracts one
     * from their indices).  Returns the element that was removed from the
     * list.<p>
     *
     * This implementation always throws an
     * <tt>UnsupportedOperationException</tt>.
     *
     * @param index the index of the element to remove.
     * @return the element previously at the specified position.
     * 
     * @throws UnsupportedOperationException if the <tt>remove</tt> method is
     *		  not supported by this list.
     * @throws IndexOutOfBoundsException if the specified index is out of
     * 		  range (<tt>index &lt; 0 || index &gt;= size()</tt>).
     */
    public Object remove(int index) {
	throw new UnsupportedOperationException();
    }


    // Search Operations

    /**
     * Returns the index in this list of the first occurence of the specified
     * element, or -1 if the list does not contain this element.  More
     * formally, returns the lowest index <tt>i</tt> such that <tt>(o==null ?
     * get(i)==null : o.equals(get(i)))</tt>, or -1 if there is no such
     * index.<p>
     *
     * This implementation first gets a list iterator (with
     * <tt>listIterator()</tt>).  Then, it iterates over the list until the
     * specified element is found or the end of the list is reached.
     *
     * @param o element to search for.
     * 
     * @return the index in this List of the first occurence of the specified
     * 	       element, or -1 if the List does not contain this element.
     */
    public int indexOf(Object o) {
	ListIterator e = listIterator();
	if (o==null) {
	    while (e.hasNext())
		if (e.next()==null)
		    return e.previousIndex();
	} else {
	    while (e.hasNext())
		if (o.equals(e.next()))
		    return e.previousIndex();
	}
	return -1;
    }

    /**
     * Returns the index in this list of the last occurence of the specified
     * element, or -1 if the list does not contain this element.  More
     * formally, returns the highest index <tt>i</tt> such that <tt>(o==null ?
     * get(i)==null : o.equals(get(i)))</tt>, or -1 if there is no such
     * index.<p>
     *
     * This implementation first gets a list iterator that points to the end
     * of the list (with listIterator(size())).  Then, it iterates backwards
     * over the list until the specified element is found, or the beginning of
     * the list is reached.
     *
     * @param o element to search for.
     * 
     * @return the index in this list of the last occurence of the specified
     * 	       element, or -1 if the list does not contain this element.
     */
    public int lastIndexOf(Object o) {
	ListIterator e = listIterator(size());
	if (o==null) {
	    while (e.hasPrevious())
		if (e.previous()==null)
		    return e.nextIndex();
	} else {
	    while (e.hasPrevious())
		if (o.equals(e.previous()))
		    return e.nextIndex();
	}
	return -1;
    }


    // Bulk Operations

    /**
     * Removes all of the elements from this collection (optional operation).
     * The collection will be empty after this call returns (unless it throws
     * an exception).<p>
     *
     * This implementation calls <tt>removeRange(0, size())</tt>.<p>
     *
     * Note that this implementation throws an
     * <tt>UnsupportedOperationException</tt> unless <tt>remove(int
     * index)</tt> or <tt>removeRange(int fromIndex, int toIndex)</tt> is
     * overridden.
     *
     * @throws UnsupportedOperationException if the <tt>clear</tt> method is
     * 		  not supported by this Collection.
     */
    public void clear() {
        removeRange(0, size());
    }

    /**
     * Inserts all of the elements in the specified collection into this list
     * at the specified position (optional operation).  Shifts the element
     * currently at that position (if any) and any subsequent elements to the
     * right (increases their indices).  The new elements will appear in the
     * list in the order that they are returned by the specified collection's
     * iterator.  The behavior of this operation is unspecified if the
     * specified collection is modified while the operation is in progress.
     * (Note that this will occur if the specified collection is this list,
     * and it's nonempty.)<p>
     *
     * This implementation gets an iterator over the specified collection and
     * iterates over it, inserting the elements obtained from the iterator
     * into this list at the appropriate position, one at a time, using
     * <tt>add(int, Object)</tt>.  Many implementations will override this
     * method for efficiency.<p>
     *
     * Note that this implementation throws an
     * <tt>UnsupportedOperationException</tt> unless <tt>add(int, Object)</tt>
     * is overridden.
     *
     * @return <tt>true</tt> if this list changed as a result of the call.
     * @param index index at which to insert the first element from the
     *		    specified collection.
     * @param c elements to be inserted into this List.
     * 
     * @throws UnsupportedOperationException if the <tt>addAll</tt> method is
     *		  not supported by this list.
     * 
     * @throws ClassCastException if the class of an element of the specified