java - Unable to set reference variable in recursive call -

i using recursive method find node in binary tree using key. when find node, set reference variable(foundnode) , return. problem when read object value still null. can help.

findgivennode(root, key, foundnode, parentstack);  private boolean findgivennode(node node, int key, node foundnode, stack<node> parentstack) {     if (node == null) {         return false;     }      parentstack.add(node);     if (node.getdata() == key) {         foundnode = node;         return true;     }       boolean leftreturn = findgivennode(node.getleftchild(), key, foundnode, parentstack);     boolean rightreturn = findgivennode(node.getrightchild(), key, foundnode, parentstack);             if (leftreturn || rightreturn) {         return true;     }  else {         parentstack.pop();         return false;     } } 

java doesn't pass arguments reference, passed value. read more here

let's clarify example. make key looking integer value 21. situation @ beginning of function following:

so now, when say:

foundnode = node; // doesn't reflect outside of method 

you changing value of foundnode locally inside findgivennode() method, doesn't apply outside method. basically, local variable called foundnode references node want change , make local variable foundnode reference new node statement above. change reflected inside function. function finished, local variables don't exist anymore neither local version of foundnode. visual result:

the simple solution use wrapper function

to keep track of reference, can make simple wrapper class store reference want:

private class nodewrapper {     node foundnode;     nodewrapper() {         foundnode = null;     } } 

then can create new nodewrapper , pass function instead of foundnode

nodewrapper wrapper = new nodewrapper(); findgivennode(root, wrapper, key, parentstack); 

then inside function instead of:

foundnode = node; 

you say:

wrapper.foundnode = node; 

this way can maintain reference throughout recursion inside nodewrapper. meaning:

nodewrapper wrapper = new nodewrapper(); findgivennode(root, wrapper, key, parentstack); // @ point, wrapper.foundnode hold reference node need // or null if node wasn't found 

on note, above method have function prototype:

findgivennode(root, key, foundnode, parentstack); 

seems still used c/c++ :)

this unnecessary in java, can read this question thread reasoning behind or google it.