AbstractList類源代碼欣賞

package java.util;


public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E> {

    protected AbstractList() {
    }

    /**
     * 添加元素方法
     */
    public boolean add(E e) {
	add(size(), e);
	return true;
    }

    /**
     * 獲取元素的抽象方法
     */
    abstract public E get(int index);

    /**
     * 根據下標設置元素的方法
     */
    public E set(int index, E element) {
	throw new UnsupportedOperationException();
    }

    /**
     * 根據下標添加元素的方法
     */
    public void add(int index, E element) {
	throw new UnsupportedOperationException();
    }

    /**
     * 根據下標刪除元素的方法
     */
    public E remove(int index) {
	throw new UnsupportedOperationException();
    }


    // Search Operations

    /**
     * 返回列表中某個元素第一次出現的索引位置的方法
     */
    public int indexOf(Object o) {
	ListIterator<E> 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;
    }

    /**
     *返回列表中某個元素最後一次出現的索引位置的方法
     */
    public int lastIndexOf(Object o) {
	ListIterator<E> 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;
    }


    /**
     * 清除列表中的所有元素
     */
    public void clear() {
        removeRange(0, size());
    }

    /**
     * 從指定位置開始將Collection中的元素按迭代順序加入到列表中
     */
    public boolean addAll(int index, Collection<? extends E> c) {
	boolean modified = false;
	Iterator<? extends E> e = c.iterator();
	while (e.hasNext()) {
	    add(index++, e.next());
	    modified = true;
	}
	return modified;
    }



    /**
     * 返回內部實現的迭代器類Itr
     */
    public Iterator<E> iterator() {
	return new Itr();
    }

    /**
     *繼承ListIterator類的方法
     */
    public ListIterator<E> listIterator() {
	return listIterator(0);
    }

    /**
     * 繼承ListIterator類的方法
     */
    public ListIterator<E> listIterator(final int index) {
	if (index<0 || index>size())
	  throw new IndexOutOfBoundsException("Index: "+index);

	return new ListItr(index);
    }

     /**
     * 私有的內部類，實現了自己的Itertor
     */

    private class Itr implements Iterator<E> {
	/**
	 *調用next方法返回的元素索引值
	 */
	int cursor = 0;

	/**
	 * 調用next方法或者previous方法時返回的索引值，當調用deleted方法時該值重新置-1		 */
	int lastRet = -1;

	/**
	 * 列表的修改次數
	 */
	int expectedModCount = modCount;

	public boolean hasNext() {
            return cursor != size();
	}

	public E next() {
            checkForComodification();
	    try {
		E next = get(cursor);
		lastRet = cursor++;
		return next;
	    } catch (IndexOutOfBoundsException e) {
		checkForComodification();
		throw new NoSuchElementException();
	    }
	}

	public void remove() {
	    if (lastRet == -1)
		throw new IllegalStateException();
            checkForComodification();

	    try {
		AbstractList.this.remove(lastRet);
		if (lastRet < cursor)
		    cursor--;
		lastRet = -1;
		expectedModCount = modCount;
	    } catch (IndexOutOfBoundsException e) {
		throw new ConcurrentModificationException();
	    }
	}

	final void checkForComodification() {
	    if (modCount != expectedModCount)
		throw new ConcurrentModificationException();
	}
    }

/**
      * 私有的內部類，實現了自己的列表迭代器類
     */

    private class ListItr extends Itr implements ListIterator<E> {
	ListItr(int index) {
	    cursor = index;
	}

	public boolean hasPrevious() {
	    return cursor != 0;
	}

        public E previous() {
            checkForComodification();
            try {
                int i = cursor - 1;
                E previous = get(i);
                lastRet = cursor = i;
                return previous;
            } catch (IndexOutOfBoundsException e) {
                checkForComodification();
                throw new NoSuchElementException();
            }
        }

	public int nextIndex() {
	    return cursor;
	}

	public int previousIndex() {
	    return cursor-1;
	}

	public void set(E e) {
	    if (lastRet == -1)
		throw new IllegalStateException();
            checkForComodification();

	    try {
		AbstractList.this.set(lastRet, e);
		expectedModCount = modCount;
	    } catch (IndexOutOfBoundsException ex) {
		throw new ConcurrentModificationException();
	    }
	}

	public void add(E e) {
            checkForComodification();

	    try {
		AbstractList.this.add(cursor++, e);
		lastRet = -1;
		expectedModCount = modCount;
	    } catch (IndexOutOfBoundsException ex) {
		throw new ConcurrentModificationException();
	    }
	}
    }

    /**
     * 返回指定位置的列表視圖
     */
    public List<E> subList(int fromIndex, int toIndex) {
        return (this instanceof RandomAccess ?
                new RandomAccessSubList<E>(this, fromIndex, toIndex) :
                new SubList<E>(this, fromIndex, toIndex));
    }


    /**
     * 比較的方法
     */
    public boolean equals(Object o) {
	if (o == this)
	    return true;
	if (!(o instanceof List))
	    return false;

	ListIterator<E> e1 = listIterator();
	ListIterator e2 = ((List) o).listIterator();
	while(e1.hasNext() && e2.hasNext()) {
	    E o1 = e1.next();
	    Object o2 = e2.next();
	    if (!(o1==null ? o2==null : o1.equals(o2)))
		return false;
	}
	return !(e1.hasNext() || e2.hasNext());
    }

    /**
     * 重寫的hashcode方法
     */
    public int hashCode() {
	int hashCode = 1;
	Iterator<E> i = iterator();
	while (i.hasNext()) {
	    E obj = i.next();
	    hashCode = 31*hashCode + (obj==null ? 0 : obj.hashCode());
	}
	return hashCode;
    }

    /**
     *刪除指定區間元素的方法
     */
    protected void removeRange(int fromIndex, int toIndex) {
        ListIterator<E> it = listIterator(fromIndex);
        for (int i=0, n=toIndex-fromIndex; i<n; i++) {
            it.next();
            it.remove();
        }
    }

    /**
     * 列表結構被修改的次數，比如列表的size變化或者打亂列表使得迭代結果不正確
     */
    protected transient int modCount = 0;
}

/**
     * 子列表類
     */

class SubList<E> extends AbstractList<E> {
    private AbstractList<E> l;
    private int offset;
    private int size;
    private int expectedModCount;

    SubList(AbstractList<E> list, int fromIndex, int toIndex) {
        if (fromIndex < 0)
            throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
        if (toIndex > list.size())
            throw new IndexOutOfBoundsException("toIndex = " + toIndex);
        if (fromIndex > toIndex)
            throw new IllegalArgumentException("fromIndex(" + fromIndex +
                                               ") > toIndex(" + toIndex + ")");
        l = list;
        offset = fromIndex;
        size = toIndex - fromIndex;
        expectedModCount = l.modCount;
    }

    public E set(int index, E element) {
        rangeCheck(index);
        checkForComodification();
        return l.set(index+offset, element);
    }

    public E get(int index) {
        rangeCheck(index);
        checkForComodification();
        return l.get(index+offset);
    }

    public int size() {
        checkForComodification();
        return size;
    }

    public void add(int index, E element) {
        if (index<0 || index>size)
            throw new IndexOutOfBoundsException();
        checkForComodification();
        l.add(index+offset, element);
        expectedModCount = l.modCount;
        size++;
        modCount++;
    }

    public E remove(int index) {
        rangeCheck(index);
        checkForComodification();
        E result = l.remove(index+offset);
        expectedModCount = l.modCount;
        size--;
        modCount++;
        return result;
    }

    protected void removeRange(int fromIndex, int toIndex) {
        checkForComodification();
        l.removeRange(fromIndex+offset, toIndex+offset);
        expectedModCount = l.modCount;
        size -= (toIndex-fromIndex);
        modCount++;
    }

    public boolean addAll(Collection<? extends E> c) {
        return addAll(size, c);
    }

    public boolean addAll(int index, Collection<? extends E> c) {
        if (index<0 || index>size)
            throw new IndexOutOfBoundsException(
                "Index: "+index+", Size: "+size);
        int cSize = c.size();
        if (cSize==0)
            return false;

        checkForComodification();
        l.addAll(offset+index, c);
        expectedModCount = l.modCount;
        size += cSize;
        modCount++;
        return true;
    }

    public Iterator<E> iterator() {
        return listIterator();
    }

    public ListIterator<E> listIterator(final int index) {
        checkForComodification();
        if (index<0 || index>size)
            throw new IndexOutOfBoundsException(
                "Index: "+index+", Size: "+size);

        return new ListIterator<E>() {
            private ListIterator<E> i = l.listIterator(index+offset);

            public boolean hasNext() {
                return nextIndex() < size;
            }

            public E next() {
                if (hasNext())
                    return i.next();
                else
                    throw new NoSuchElementException();
            }

            public boolean hasPrevious() {
                return previousIndex() >= 0;
            }

            public E previous() {
                if (hasPrevious())
                    return i.previous();
                else
                    throw new NoSuchElementException();
            }

            public int nextIndex() {
                return i.nextIndex() - offset;
            }

            public int previousIndex() {
                return i.previousIndex() - offset;
            }

            public void remove() {
                i.remove();
                expectedModCount = l.modCount;
                size--;
                modCount++;
            }

            public void set(E e) {
                i.set(e);
            }

            public void add(E e) {
                i.add(e);
                expectedModCount = l.modCount;
                size++;
                modCount++;
            }
        };
    }

    public List<E> subList(int fromIndex, int toIndex) {
        return new SubList<E>(this, fromIndex, toIndex);
    }

    private void rangeCheck(int index) {
        if (index<0 || index>=size)
            throw new IndexOutOfBoundsException("Index: "+index+
                                                ",Size: "+size);
    }

    private void checkForComodification() {
        if (l.modCount != expectedModCount)
            throw new ConcurrentModificationException();
    }
}

/**
 * 具有隨機訪問性質的子列表類
*/

class RandomAccessSubList<E> extends SubList<E> implements RandomAccess {
    RandomAccessSubList(AbstractList<E> list, int fromIndex, int toIndex) {
        super(list, fromIndex, toIndex);
    }

    public List<E> subList(int fromIndex, int toIndex) {
        return new RandomAccessSubList<E>(this, fromIndex, toIndex);
    }
}