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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* 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).
*
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package javax.swing.text;
import java.util.Stack;
import java.util.Enumeration;
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
/**
* <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 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 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 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.
Params: - root – the root Element.
/**
* Creates a new ElementIterator.
*
* @param root the root Element.
*/
public ElementIterator(Element root) {
this.root = root;
}
Clones the ElementIterator.
Returns: a cloned ElementIterator Object.
/**
* 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.
Returns: an Element.
/**
* 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.
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 Element.
*
* @return element on top of the stack or
* <code>null</code> if the root element is <code>null</code>
*/
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 Element. The strategy
* used to locate the next element is
* a depth-first search.
*
* @return the next element or <code>null</code>
* 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 Element. If however the current
* element is the last element, or the current element
* is null, then null is returned.
*
* @return previous <code>Element</code> 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</code> 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;
}
}
}
}