Complete the ExpressionTree.java class in jss2 package: work on constructors and

Question

Complete the ExpressionTree.java class in jss2 package: work on constructors and evaluateNode() method. You may use the child class LinkedBinaryTree<T> as reference.

/**
* ExpressionTree represents an expression tree of operators and operands.
*
*
*/

package jss2;

public class ExpressionTree extends LinkedBinaryTree<ExpressionTreeObj>
{
/**
* Creates an empty expression tree.
*/
public ExpressionTree()
{
super();
}

/**
* Constructs a expression tree from the two specified expression
* trees.
*
* @param element the expression tree for the center
* @param leftSubtree the expression tree for the left subtree
* @param rightSubtree the expression tree for the right subtree
*/
public ExpressionTree (ExpressionTreeObj element,
ExpressionTree leftSubtree, ExpressionTree rightSubtree)
{

root = new BinaryTreeNode<T> (element);
count = 1;
if (leftSubtree != null)
{
count = count + leftSubtree.size();
root.left = leftSubtree.root;

}
else
root.left = null;

if (rightSubtree !=null)
{
count = count + rightSubtree.size();
root.right = rightSubtree.root;
}
else
root.right=null;

}



/**
* Evaluates the expression tree by calling the recursive
* evaluateNode method.
*
* @return the integer evaluation of the tree
*/
public int evaluateTree()
{
return evaluateNode(root);
}

/**
* Recursively evaluates each node of the tree.
*
* @param root the root of the tree to be evaluated
* @return the integer evaluation of the tree
*/
public int evaluateNode(BinaryTreeNode root)
{
int result;
int operand1;
int operand2;
ExpressionTreeObj temp;

if (root==null)
result = 0;
else
{
temp = (ExpressionTreeObj)root.element;

if (temp.isOperator(temp))
{
operand1 = evaluateNode(root.left);
operand2 = evaluateNode(root.right);
result = computeTerm(temp.getOperator(), operand1, operand2);
}
else
result = temp.getValue();
}

return result;

}



/**
* Evaluates a term consisting of an operator and two operands.
*
* @param operator the operator for the expression
* @param operand1 the first operand for the expression
* @param operand2 the second operand for the expression
*/
private static int computeTerm(char operator, int operand1, int operand2)
{
int result=0;

if (operator == '+')
result = operand1 + operand2;

else if (operator == '-')
result = operand1 - operand2;
else if (operator == '*')
result = operand1 * operand2;
else
result = operand1 / operand2;

return result;
}
}

I believe I have that right but now there is where I am stuck

Design and implement a java program called PostfixEvaluatorXXX.java which includes a solve() method that builds the expression tree from the read-in postfix expression and evaluate the tree; We assume only arithmetic operations of + - * /; Save your program in the same directory as the jss2 (that is, outside of jss2).

Create a driver program called PostfixXXX.java (where XXX are your initials) which reads in a line of postfix expression (using BufferedReader class) and call the solve() method of PostfixEvaluatorXXX.java class to evaluate the postfix expression and print out the result; Save your driver in the same directory as the jss2 (that is, outside of jss2).

Explanation / Answer

Does this help? This is the only part of your query I could follow..

Postfix Evaluator:

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