Java Recursive Depth First Search
The context of this code example is not very clear, so in my remarks below I will suppose that the code is about a generic implementation of depth-first search.

TreeNode

If this is a generic implementation, my first question then is why TreeNode interface is there? This interface is part of Swing API, which has it own sphere of application. The objects implementing this interface may (or may not) be convenient here; anyway, they tend to be used in Swing/GUI-related situations and I'd not interfere with their scope for a generic case.

There is also something even more important concerning TreeNode. As you know, it has children() method which returns an Enumeration. This type is a very old Java thing (since JDK1.0), introduced even before Collections, and currently it looks like a rudiment. And it's not very pleasant to iterate on.

But if you still need/want to keep TreeNode, a type bound mark Enumeration&lt;TreeNode&gt; should be added, in order to avoid compilation warnings.

To replace TreeNode, I'd suggest to create a short and concise Node class, which points to a Collection (or even a Stream) of children Nodes and overrides hashCode and equals methods. This class would also be useful in other examples of your article.

Code Blocks

I understand that conciseness and lack of extra space is the priority in this code, but when I see this

if(top == null || find == null) return false;
else if(top.equals(find)) return true;


it looks for me more like code obfuscation. Please find a place to use braces:

if (top == null || find == null) {
    return false;
}
else if (top.equals(find)) {
     return true;
}


It can be very confusing and error-prone when the instruction that immediately follows a condition is not wrapped in a block.