Java example source code file (ElementIterator.java)

This example Java source code file (ElementIterator.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

attributeset, cloneable, clonenotsupportedexception, element, elementiterator, enumeration, internalerror, object, stackitem, string, util

The ElementIterator.java Java example source code

/*
 * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javax.swing.text;

import java.util.Stack;
import java.util.Enumeration;

/**
 * <p>
 * ElementIterator, as the name suggests, iterates over the Element
 * tree.  The constructor can be invoked with either Document or an Element
 * as an argument.  If the constructor is invoked with a Document as an
 * argument then the root of the iteration is the return value of
 * document.getDefaultRootElement().
 *
 * The iteration happens in a depth-first manner.  In terms of how
 * boundary conditions are handled:
 * a) if next() is called before first() or current(), the
 *    root will be returned.
 * b) next() returns null to indicate the end of the list.
 * c) previous() returns null when the current element is the root
 *    or next() has returned null.
 *
 * The ElementIterator does no locking of the Element tree. This means
 * that it does not track any changes.  It is the responsibility of the
 * user of this class, to ensure that no changes happen during element
 * iteration.
 *
 * Simple usage example:
 *
 *    public void iterate() {
 *        ElementIterator it = new ElementIterator(root);
 *        Element elem;
 *        while (true) {
 *           if ((elem = next()) != null) {
 *               // process element
 *               System.out.println("elem: " + elem.getName());
 *           } else {
 *               break;
 *           }
 *        }
 *    }
 *
 * @author Sunita Mani
 *
 */

public class ElementIterator implements Cloneable {


    private Element root;
    private Stack<StackItem> elementStack = null;

    /**
     * The StackItem class stores the element
     * as well as a child index.  If the
     * index is -1, then the element represented
     * on the stack is the element itself.
     * Otherwise, the index functions as as index
     * into the vector of children of the element.
     * In this case, the item on the stack
     * represents the "index"th child of the element
     *
     */
    private class StackItem implements Cloneable {
        Element item;
        int childIndex;

        private StackItem(Element elem) {
            /**
             * -1 index implies a self reference,
             * as opposed to an index into its
             * list of children.
             */
            this.item = elem;
            this.childIndex = -1;
        }

        private void incrementIndex() {
            childIndex++;
        }

        private Element getElement() {
            return item;
        }

        private int getIndex() {
            return childIndex;
        }

        protected Object clone() throws java.lang.CloneNotSupportedException {
            return super.clone();
        }
    }

    /**
     * Creates a new ElementIterator. The
     * root element is taken to get the
     * default root element of the document.
     *
     * @param document a Document.
     */
    public ElementIterator(Document document) {
        root = document.getDefaultRootElement();
    }


    /**
     * Creates a new ElementIterator.
     *
     * @param root the root Element.
     */
    public ElementIterator(Element root) {
        this.root = root;
    }


    /**
     * Clones the ElementIterator.
     *
     * @return a cloned ElementIterator Object.
     */
    public synchronized Object clone() {

        try {
            ElementIterator it = new ElementIterator(root);
            if (elementStack != null) {
                it.elementStack = new Stack<StackItem>();
                for (int i = 0; i < elementStack.size(); i++) {
                    StackItem item = elementStack.elementAt(i);
                    StackItem clonee = (StackItem)item.clone();
                    it.elementStack.push(clonee);
                }
            }
            return it;
        } catch (CloneNotSupportedException e) {
            throw new InternalError(e);
        }
    }


    /**
     * Fetches the first element.
     *
     * @return an Element.
     */
    public Element first() {
        // just in case...
        if (root == null) {
            return null;
        }

        elementStack = new Stack<StackItem>();
        if (root.getElementCount() != 0) {
            elementStack.push(new StackItem(root));
        }
        return root;
    }

    /**
     * Fetches the current depth of element tree.
     *
     * @return the depth.
     */
    public int depth() {
        if (elementStack == null) {
            return 0;
        }
        return elementStack.size();
    }


    /**
     * Fetches the current Element.
     *
     * @return element on top of the stack or
     *          <code>null if the root element is null
     */
    public Element current() {

        if (elementStack == null) {
            return first();
        }

        /*
          get a handle to the element on top of the stack.
        */
        if (! elementStack.empty()) {
            StackItem item = elementStack.peek();
            Element elem = item.getElement();
            int index = item.getIndex();
            // self reference
            if (index == -1) {
                return elem;
            }
            // return the child at location "index".
            return elem.getElement(index);
        }
        return null;
    }


    /**
     * Fetches the next Element. The strategy
     * used to locate the next element is
     * a depth-first search.
     *
     * @return the next element or <code>null
     *          at the end of the list.
     */
    public Element next() {

        /* if current() has not been invoked
           and next is invoked, the very first
           element will be returned. */
        if (elementStack == null) {
            return first();
        }

        // no more elements
        if (elementStack.isEmpty()) {
            return null;
        }

        // get a handle to the element on top of the stack

        StackItem item = elementStack.peek();
        Element elem = item.getElement();
        int index = item.getIndex();

        if (index+1 < elem.getElementCount()) {
            Element child = elem.getElement(index+1);
            if (child.isLeaf()) {
                /* In this case we merely want to increment
                   the child index of the item on top of the
                   stack.*/
                item.incrementIndex();
            } else {
                /* In this case we need to push the child(branch)
                   on the stack so that we can iterate over its
                   children. */
                elementStack.push(new StackItem(child));
            }
            return child;
        } else {
            /* No more children for the item on top of the
               stack therefore pop the stack. */
            elementStack.pop();
            if (!elementStack.isEmpty()) {
                /* Increment the child index for the item that
                   is now on top of the stack. */
                StackItem top = elementStack.peek();
                top.incrementIndex();
                /* We now want to return its next child, therefore
                   call next() recursively. */
                return next();
            }
        }
        return null;
    }


    /**
     * Fetches the previous Element. If however the current
     * element is the last element, or the current element
     * is null, then null is returned.
     *
     * @return previous <code>Element if available
     *
     */
    public Element previous() {

        int stackSize;
        if (elementStack == null || (stackSize = elementStack.size()) == 0) {
            return null;
        }

        // get a handle to the element on top of the stack
        //
        StackItem item = elementStack.peek();
        Element elem = item.getElement();
        int index = item.getIndex();

        if (index > 0) {
            /* return child at previous index. */
            return getDeepestLeaf(elem.getElement(--index));
        } else if (index == 0) {
            /* this implies that current is the element's
               first child, therefore previous is the
               element itself. */
            return elem;
        } else if (index == -1) {
            if (stackSize == 1) {
                // current is the root, nothing before it.
                return null;
            }
            /* We need to return either the item
               below the top item or one of the
               former's children. */
            StackItem top = elementStack.pop();
            item = elementStack.peek();

            // restore the top item.
            elementStack.push(top);
            elem = item.getElement();
            index = item.getIndex();
            return ((index == -1) ? elem : getDeepestLeaf(elem.getElement
                                                          (index)));
        }
        // should never get here.
        return null;
    }

    /**
     * Returns the last child of <code>parent that is a leaf. If the
     * last child is a not a leaf, this method is called with the last child.
     */
    private Element getDeepestLeaf(Element parent) {
        if (parent.isLeaf()) {
            return parent;
        }
        int childCount = parent.getElementCount();
        if (childCount == 0) {
            return parent;
        }
        return getDeepestLeaf(parent.getElement(childCount - 1));
    }

    /*
      Iterates through the element tree and prints
      out each element and its attributes.
    */
    private void dumpTree() {

        Element elem;
        while (true) {
            if ((elem = next()) != null) {
                System.out.println("elem: " + elem.getName());
                AttributeSet attr = elem.getAttributes();
                String s = "";
                Enumeration names = attr.getAttributeNames();
                while (names.hasMoreElements()) {
                    Object key = names.nextElement();
                    Object value = attr.getAttribute(key);
                    if (value instanceof AttributeSet) {
                        // don't go recursive
                        s = s + key + "=**AttributeSet** ";
                    } else {
                        s = s + key + "=" + value + " ";
                    }
                }
                System.out.println("attributes: " + s);
            } else {
                break;
            }
        }
    }
}