Java Enterprise Best Practices

Avoid Class Comparisons

If you’ve worked with DOM, you know that one of the most common operations is tree walking. In fact, the last best practice showed a helper method to aid in this by walking a node’s children to get its textual content. This tree walking is generally accomplished through the org.w3c.dom.Node interface, as all DOM structures implement (actually, they extend, and your parser provides implementations of those interfaces) this base interface.

The problem is that there are several methods for determining a node’s type, and then reacting to that type. Most Java developers familiar with polymorphism and inheritance would immediately use the methods provided around the Java Class class. Using that approach, you might end up with code such as that in Example 5-13.

Example 5-13. Using Java class comparison

NodeList children = rootNode.getChildNodes(  );
   
// Figure out which node type you have and work with it.
for (int i=0; i<children.getLength(  ); i++) {
    Node child = children.item(i);
   
    if (child.getClass(  ).equals(org.w3c.dom.Element.class)) {
        Element element = (Element)child;
        // Do something with the element.
    } else if (child.getClass(  ).equals(org.w3c.dom.Text.class)) {
        Text text = (Text)child;
        // Do something with the text node.
    } else if (child.getClass(  ).equals(org.w3c.dom.Comment.class)) {
        Comment comment = (Comment)child;
        // Do something with the comment.
    } // etc . . . 
}

In a similar vein, I’ve also seen code that looks similar to Example 5-14.

Example 5-14. Using ...