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package javax.swing.text;
import java.util.Enumeration;
import java.util.Stack;
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:
- if
next is called before first or current, the root will be returned next returns null to indicate the end of the list 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 = it.next()) != null) {
// process element
System.out.println("elem: " + elem.getName());
} else {
break;
}
}
}
Author: Sunita Mani
/**
* {@code ElementIterator}, as the name suggests, iterates over the
* {@code Element} tree. The constructor can be invoked with either
* {@code Document} or an {@code Element} as an argument. If the constructor is
* invoked with a {@code Document} as an argument then the root of the iteration
* is the return value of {@code document.getDefaultRootElement()}.
* <p>
* The iteration happens in a depth-first manner. In terms of how boundary
* conditions are handled:
* <ul>
* <li>if {@link #next} is called before {@link #first} or {@link #current},
* the root will be returned
* <li>{@link #next} returns {@code null} to indicate the end of the list
* <li>{@link #previous} returns {@code null} when the current element is the
* root or {@link #next} has returned {@code null}
* </ul>
* <p>
* The {@code ElementIterator} does no locking of the {@code 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.
* <p>
* Simple usage example:
* <pre>{@code public void iterate() {
* ElementIterator it = new ElementIterator(root);
* Element elem;
* while (true) {
* if ((elem = it.next()) != null) {
* // process element
* System.out.println("elem: " + elem.getName());
* } else {
* break;
* }
* }
* }}</pre>
*
* @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 an 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. /**
* The {@code 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 an 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. Params: - document – a
Document
/**
* Creates a new {@code ElementIterator}. The root element is taken to get
* the default root element of the document.
*
* @param document a {@code Document}
*/
public ElementIterator(Document document) {
root = document.getDefaultRootElement();
}
Creates a new ElementIterator. Params: - root – the root
Element
/**
* Creates a new {@code ElementIterator}.
*
* @param root the root {@code Element}
*/
public ElementIterator(Element root) {
this.root = root;
}
Clones the ElementIterator. Returns: a cloned ElementIterator Object
/**
* Clones the {@code ElementIterator}.
*
* @return a cloned {@code 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.
Returns: an Element
/**
* Fetches the first element.
*
* @return an {@code 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.
Returns: the depth
/**
* 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. Returns: element on top of the stack or null if the root element is null
/**
* Fetches the current {@code Element}.
*
* @return element on top of the stack or {@code null} if the root element
* is {@code 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. Returns: the next element or null at the end of the list
/**
* Fetches the next {@code 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. Returns: previous Element if available
/**
* Fetches the previous {@code Element}. If however the current element is
* the last element, or the current element is {@code null}, then
* {@code 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 parent that is a leaf. If the last child is a not a leaf, this method is called with the last child. /**
* 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.
/**
* 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;
}
}
}
}