data structure using java (not c++)

Write a java method that receive a reference to a binary tree root and then prints the values that exist in nodes that can be seen if you look at the tree from its right side (a node can be seen from the right side if there is no other node in its right at the same level. for example consider the following tree: 2 3 6 7 8 the output will be: 1, 3, 6, 8