Question

I have the following method definition which is intended to search a JSON object for a given key and return either the JSONObject or the String value of that key. To ensure it searches through every level of the JSON object I have made it recursive, but only in the event that a deeper JSONObject can be returned. The compiler complains that this must return an Object because I have declared that return type. Fine. In two cases I am returning an object but I think its problem is that in some circumstances it will not return anything. If I add a final return false, or something, it will pass the compiler check but a call to this method will always then (eventually) return false making it useless. I am not used to a strictly typed language like Java so I haven’t encountered a similar issue before. Any pointers would be appreciated.

public Object find(String contentId, JSONObject node) {
    JSONObject currentNode = (node != null) ? node : this.txtContent;
    Iterator<?> nodeKeys = currentNode.keys();

    while ( nodeKeys.hasNext() ){

        try {
            String key = (String) nodeKeys.next();

            if (key.equals(contentId)) {
                if (currentNode.get(key) instanceof JSONObject) {
                    return currentNode.getJSONObject(key);
                } else {
                    return currentNode.getString(key);
                }
            } else if (currentNode.get(key) instanceof JSONObject) {
                find(contentId, currentNode.getJSONObject(key));
            }
        } catch (JSONException e) {
            throw new RuntimeException(e);
        }
    }
}

Answer 1

Let’s see, you should use the value returned by the find call and return null if not found:

public Object find(String contentId, JSONObject node) {
    JSONObject currentNode = (node != null) ? node : this.txtContent;
    Iterator<?> nodeKeys = currentNode.keys();

    while ( nodeKeys.hasNext() ){

        try {
            String key = (String) nodeKeys.next();

            if (key.equals(contentId)) {
                if (currentNode.get(key) instanceof JSONObject) {
                    return currentNode.getJSONObject(key);
                } else {
                    return currentNode.getString(key);
                }
            } else if (currentNode.get(key) instanceof JSONObject) {
                Object foundObj = find(contentId, currentNode.getJSONObject(key));
                if (foundObj!=null) {
                    return foundObj;
                }
            }
        } catch (JSONException e) {
            throw new RuntimeException(e);
        }
    }
    return null;
}