private static final String SAMPLE_PRICE = "895"; public void testSimpleTagWithOneAttributeAndValue() { TagNode priceTag = new TagNode("price"); priceTagaddAttribute("currency", "USD"); priceTagaddValue(SAMPLE_PRICE); String expected = "<price currency=" + "'" + "USD" + "'>" + SAMPLE_PRICE + "</price>"; assertEquals("price XML", expected, priceTagtoString()); }

Here's the code to make the test pass:

This document was created by an unregistered ChmMagic, please go to http://wwwbisentercom to register it Thanks

public class TagNode { private String name = ""; private String value = ""; private StringBuffer attributes;

public TagNode(String name) { thisname = name; attributes = new StringBuffer(""); }

public void addAttribute(String attribute, String value) { attributesappend(" "); attributesappend(attribute); attributesappend("='"); attributesappend(value); attributesappend("'"); }

public void addValue(String value) { thisvalue = value; }

public String toString() { String result; result = "<" + name + attributes + ">" + value + "</" + name + ">"; return result; }

This document was created by an unregistered ChmMagic, please go to http://wwwbisentercom to register it Thanks

2 I can now replace the implicit leaf in thegetContents() method with a TagNode instance:

public class OrdersWriter private void writePriceTo(StringBuffer xml, Product product) {

TagNode priceNode = new TagNode("price"); priceNodeaddAttribute("currency", currencyFor(product)); priceNodeaddValue(priceFor(product)); xmlappend(priceNodetoString());

xmlappend(" currency='"); xmlappend("<price");

xmlappend(currencyFor(product));

xmlappend("'>");

xmlappend(productgetPrice());

xmlappend("</price>");

I compile and run tests to ensure that the implicit tree is still rendered correctly 3 Because TagNode models all of the implicit leaves in the XML, I do not need to repeat steps 1 and 2 to convert additional implicit leaves to leaf nodes, nor do I need to ensure that all newly created leaf nodes share a common interface they already do 4 Now I identify an implicit parent by studying fragments of test code I find that a <product> tag is a parent for a<price> tag, an <order> tag is a parent for a<product> tag, and an <orders> tag is a parent for an <order> tag Yet because each of these implicit parents is already so similar in nature to the implicit leaf identified earlier, I see that I can produce a parent node by adding child-handling support to TagNode I follow test-driven development to produce this new code Here's the first test I write:

public void testCompositeTagOneChild() { TagNode productTag = new TagNode("product"); productTagadd(new TagNode("price")); String expected = "<product>" +

This document was created by an unregistered ChmMagic, please go to http://wwwbisentercom to register it Thanks

"<price>" + "</price>" + "</product>"; assertEquals("price XML", expected, productTagtoString()); }

And here's code to pass that test:

private List children;

public String toString() { String result; result = "<" + name + attributes + ">";

Iterator it = children()iterator(); while (ithasNext()) { TagNode node = (TagNode)itnext(); result += nodetoString(); }

result += value; result += "</" + name + ">"; return result; }

private List children() { if (children == null) children = new ArrayList(); return children; }

public void add(TagNode child) { children()add(child); }

Here's a slightly more robust test:

This document was created by an unregistered ChmMagic, please go to http://wwwbisentercom to register it Thanks

public void testAddingChildrenAndGrandchildren() { String expected = "<orders>" + "<order>" + "<product>" + "</product>" + "</order>" + "</orders>"; TagNode ordersTag = new TagNode("orders"); TagNode orderTag = new TagNode("order"); TagNode productTag = new TagNode("product"); ordersTagadd(orderTag); orderTagadd(productTag); assertEquals("price XML", expected, ordersTagtoString()); }

I continue writing and running tests until I'm satisfied thatTagNode can behave as a proper parent node When I'm done, TagNode is a class that can play all three participants in the Composite pattern:

5 Now I replace every occurrence of the implicit parent with code that uses a parent node instance, outfitted with the correct

This document was created by an unregistered ChmMagic, please go to http://wwwbisentercom to register it Thanks

leaf node instance(s) Here's an example:

public class OrdersWriter private void writeProductsTo(StringBuffer xml, Order order) { for (int j=0; j < ordergetProductCount(); j++) { Product product = ordergetProduct(j);

TagNode productTag = new TagNode("product"); productTagaddAttribute("id", productgetID()); productTagaddAttribute("color", colorFor(product));

if (productgetSize() != ProductSizeNOT_APPLICABLE)

productTagaddAttribute("size", sizeFor(product)); writePriceTo(productTag, product); productTagaddValue(productgetName());

xmlappend(

productTagtoString());

private void writePriceTo(TagNode productTag, Product product) {

TagNode priceTag = new TagNode("price"); priceTagaddAttribute("currency", currencyFor(product)); priceTagaddValue(priceFor(product));

productTagadd(priceTag);

I compile and run tests to ensure that the implicit tree still renders itself correctly 6 I repeat steps 4 and 5 for all remaining implicit parents This yields the following code, which is identical to the after code in the code sketch on the first page of this refactoring, except that the code is broken up into smaller methods:

public class OrdersWriter public String getContents() { StringBuffer xml = new StringBuffer(); writeOrderTo(xml); return xmltoString(); } private void writeOrderTo(StringBuffer xml) { TagNode ordersTag = new TagNode("orders"); for (int i = 0; i < ordersgetOrderCount(); i++) { Order order = ordersgetOrder(i); TagNode orderTag = new TagNode("order"); orderTagaddAttribute("id", ordergetOrderId()); writeProductsTo(orderTag, order); ordersTagadd(orderTag); } xmlappend(ordersTagtoString()); }

This document was created by an unregistered ChmMagic, please go to http://wwwbisentercom to register it Thanks

private void writeProductsTo(TagNode orderTag, Order order) { for (int j=0; j < ordergetProductCount(); j++) { Product product = ordergetProduct(j); TagNode productTag = new TagNode("product"); productTagaddAttribute("id", productgetID()); productTagaddAttribute("color", colorFor(product)); if (productgetSize() != ProductSizeNOT_APPLICABLE) productTagaddAttribute("size", sizeFor(product)); writePriceTo(productTag, product); productTagaddValue(productgetName()); orderTagadd(productTag); } } private void writePriceTo(TagNode productTag, Product product) { TagNode priceNode = new TagNode("price"); priceNodeaddAttribute("currency", currencyFor(product)); priceNodeaddValue(priceFor(product)); productTagadd(priceNode); }