Java object cannot passed by ref through recursion -

the problem need write function validate whether binary tree valid binary search tree

this code:

public static boolean bettervalidbstarray(treenode node) {     wrapint lastdata = null;     return validate(lastdata, node); }  private static boolean validate(wrapint lastdata, treenode node) {     if(node == null) return true;     if(!validate(lastdata, node.getleft())) return false;     if(lastdata != null && node.getdata() <= lastdata.value) return false;     if(lastdata == null) lastdata = new wrapint();     lastdata.value = node.getdata();     if(!validate(lastdata, node.getright())) return false;      return true; }  class wrapint { int value; } 

the problem is, algorithm not working. put break points , figure out each stack call, after lastdata gets assigned value after stack call finishes, previous stack call continue lastdata = null, lastdata has real value previous stack call.

thank help.

to fix code should not if(lastdata == null) lastdata = new wrapint(); assigns reference new object method call parameter local variable each stack call, , should pass not null lastdata object used across whole recursion, changing value.