Determine instance
 

I am trying to learn some oop in java. What I am trying to do is building a binary tree to convert an ekspresion in reverse police notation to infix notation. The problem is that I have three classes, one abstract called ArithmeticNode which represents a general node, a class called ValueNode representing a leaf with no children and the last class called OperatorNode representing a node with two children.

ArithmeticNode

abstract class ArithmeticNode 

{        

        protected Object data;

        protected String infixNotation;

        

        abstract Object printNode();

        abstract String infix();

}

ValueNode

class ValueNode extends ArithmeticNode

{

        

        public ValueNode(Number value)

        {

                        super.data = value;

        }

        

        public Object printNode()

        {

                        return super.data;

        }

        

        public String infix()

        {

                super.infixNotation += super.data;

                

                return super.infixNotation;

        }

        

}

OperatorNode

class OperatorNode extends ArithmeticNode

{



        Object leftChild;

    Object rightChild;

        

        public OperatorNode(Object operator, Object LC, Object RC)

        {

                this.leftChild = LC;

                this.rightChild = RC;

                super.data = operator;

        }

        

        public String printNode()

        {

                String node = new String();

                

                node = leftChild.toString();

                node += super.data.toString();

                node += rightChild.toString();

                

                return node;

        }

        

        public String infix()

        {

                super.infixNotation += leftChild.infix();

                super.infixNotation += super.data;

                super.infixNotation += rightChild.infix();

                

                

                return super.infixNotation;

        }

                



}

The problem I am having right now, is how do I know what the children in OperatorNode is an instance of. They can be both an OperatorNode or a ValueNode. Right now I have them as Object which does not work.
So the question is: is there a way to decide what instance each child is or do I need to restructure?

Re: Determine instance
 

Check this link on how to determine what kind of class is an instance:

http://en.wikibooks.org/wiki/Java_Pr...rds/instanceof