tree - Traverse PreOrder in BinarySearchTree (Java) -

i need help. runned full code via junit still errors. think because of traverse code.

the purpose of traverse code create linkedlist in in preorder.

for example: junit says wrong

assertarrayequals( new integer[]{2, 14, 26, 86, 122, 134, 182},     arrays.copyof(tree.traversepreorder(), tree.getsize(), integer[].class)); 

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@override public object[] traversepreorder() {     binarytreenode<t> x = root;     linkedlist<object> y = new linkedlist<object>();      if (x == null) {         return null;     } else {         y.add(x.value);         y.add(travpreord(x.getleft()));         y.add(travpreord(x.getright()));     }     return y.toarray(); }  public linkedlist<object> travpreord(binarytreenode<t> x) {     binarytreenode<t> tmp = x;     linkedlist<object> space = new linkedlist<object>();      if (x == null) {         return null;     } else {         space.add(tmp.getvalue());         space.add(travpreord(x.getleft()));         space.add(travpreord(x.getright()));     }     return space; } 

you have big problem since add results of travpreord, list<object> or null if node doesn't exist.

the best solution these cases maintain overridden method non-recursive , overload method uses recursion , has argument receives container has add data:

public list<object> travpreord(binarytreenode<t> x) {     binarytreenode<t> tmp = x;     list<t> space = new linkedlist<t>();     travpreord(x, space);     return space; }  private void travpreord(binarytreenode<t> x, list<t> space) {     if (x == null) {         return;     }     space.add(tmp.getvalue());     travpreord(x.getleft(), space);     travpreord(x.getright(), space); }