无法到达的退货声明？

Question

Just got a question concerning a return statement in Java and the use of a method which should return a value from deep within a xml-statement.

public static String searchNode(Node node, Node parent, String nodeResult) {
    String nodeValue = "";

    if (node.hasChildNodes()) {
        NodeList childrens = node.getChildNodes();
        for (int i = 0; i < childrens.getLength(); i++) {
            searchNode(childrens.item(i), node, nodeResult);
        }
    } else {
        nodeValue = node.getNodeValue().trim();
        if (nodeValue.length() > 0) {
            if (parent.getNodeName().equals(nodeResult)) {
                System.out.println("YESSA: " + nodeValue);
                return "2: " + nodeValue;
            }
        }
    }
    return nodeValue;
}

And here's my question: Why is the return "2"-Statement never reached? Or let me rather ask: why is nodeValue at the end still empty? I tested it already and the code prints this "System.out.println"-thing, but never reaches the return there?! What do I have to change if I wanted the nodeValue filled in the value from the "else"-statement?

EDIT:

Ok, I tried out what you proposed but unfortunately I never get the result I wanted to have. Further description:

I have a xml-structure which looks like this:

<?xml version="1.0" encoding="UTF-8" ?>
<log>
<published>2014-03-28T15:28:36.646Z</published>
<actor>
    <objectType>person</objectType>
    <id>e1b8948f-321e-78ca-d883-80500aae71b5</id>
    <displayName>anonymized</displayName>
</actor>
<verb>update</verb>
<object>
    <objectType>concept</objectType>
    <id>a1ad6ace-c722-ffa9-f58e-b4169acdb4e3</id>
    <content>time</content>
</object>
<target>
    <objectType>conceptMap</objectType>
    <id>4b8f69e3-2914-3a1a-454e-f4c157734bd1</id>
    <displayName>my first concept map</displayName>
</target>
<generator>
    <objectType>application</objectType>
    <url>http://www.golabz.eu/content/go-lab-concept-mapper</url>
    <id>c9933ad6-dd4a-6f71-ce84-fb1676ea3aac</id>
    <displayName>ut.tools.conceptmapper</displayName>
</generator>
<provider>
    <objectType>ils</objectType>
    <url>http://graasp.epfl.ch/metawidget/1/b387b6f</url>
    <id>10548c30-72bd-0bb3-33d1-9c748266de45</id>
    <displayName>unnamed ils</displayName>
</provider>
</log>

I do the method call as I show you in the following:

searchNode(document.getFirstChild(), null, "id")

Then, I want to save the id-value of the subnode <id> from <actor> in a variable (after that the method should terminate with something like a break; , because I don't want to get all ID's. Just this single ID.

Answer 1

You don't return the result of your recursing. You should return it, or set the result.

return searchNode(childrens.item(i), node, nodeResult);

or nodeValue = searchNode(childrens.item(i), node, nodeResult);

Answer 2

You wrote a recursive method that ignores results of intermediate invocations. The return statement in question would be reached only if you start your search right at the node that you want to find.

To fix this, your recursive branch should pay attention to what's returned by recursive invocation. If you need to find the first matching child, do this:

for (int i = 0; i < childrens.getLength(); i++) {
    String tmp = searchNode(childrens.item(i), node, nodeResult);
    if (tmp != null && tmp.length() != 0) {
        return tmp;
    }
}

Answer 3

You are calling the method recursively, and each call creates its own nodeValue on the stack. Consider this:

• first you call it with the node that has one child, nodeValue is empty string
• then, in the first for loop you call the same method again, new nodeValue is created on the stack
• you return 2: something from it
• you do nothing with that return result, just return empty string in the original call

Now, you probably want to use the result from recursive calls, so try this in the for loop

nodeValue = searchNode(childrens.item(i), node, nodeResult);