Node.java

public class Node {
    public Node left;
    public Node right;
    public int value;

    public Node(int value, Node left, Node right){
        this.value = value;
        this.left = left;
        this.right = right;
    }

    public Node(int value){
        this.value = value;
    }

    public void print_depth_first(){
        System.out.printf("%d, ", this.value);
        if (this.left != null){
            this.left.print_depth_first();
        }
        if (this.right != null){
            this.right.print_depth_first();
        }
    }

    public static void main(String[] args) {
        Node n = new Node(1,
                          new Node(2,
                               new Node(3),
                               new Node(4)),
                          new Node(5));
        n.print_depth_first();
    }
}