是否可以检查可能是未初始化的变量？

Question

I'm working on a recursive method...

public BinaryTree<T> TreeMirror ( BinaryTree<T> tree ) {
   BinaryTree mirror = new BinaryTree();
   mirror = clone(tree);
   ...
   TreeMirror(...)
   ...
} 

I do not wish for the method to make mirror reference a different BinaryTree object in each recursive step, nor to repeat the mirror = clone(tree) statement after the first iteration. I'm wondering if it's possible to put in an if-statement check to see if an instance of mirror has already been initialized -- in which case the mirror = new BinaryTree() and mirror = clone(tree) statements would be skipped.

I don't think this is possible without passing mirror as an argument into the method or defining it in the class definition... but I want to make sure.

Any advice is much appreciated.

---------EDIT-----------

I am not allowed to change the method signature, so I cannot pass the object in in my implementation. I can create a mirror tree but only by modifying the original tree into a mirror which is something I want to try to avoid. I was attempting to create a new BinaryTree object that is the mirror of the original tree that is passed in but really cannot figure out how to do it recursively.

Answer 1

It's rare to see public recursive functions like that. A better solution might be to have the public method that creates the object, and then calls a private function which is recursive that just makes the necessary changes.

It's generally difficult to have the recursive function signature match what you want to show to your clients.

Answer 2

The mirror variable is local to the method, and will ALWAYS be unitialized in each call.

Passing mirror as an argument to the method is a very good option.

EDIT: If you can't modify the method signature, can you create a private method and call that to perform the recursion?

Answer 3

"I don't think this is possible without passing mirror as an argument into the method or defining it in the class definition... but I want to make sure."

Correct, that would be one way to do what you want, as mirror is not a recursion invariant.

The other way would be that your recursive algorithm clones just nodes, not entire subtrees.

Answer 4

Uri's answer is the best.... refactor it into a private method and simply initialize the mirror then invoke the private (recrsive) method passing mirror as a parameter.