// Takes an operator, pops appropriate number of operands from
// operand stack, builds them into a new subtree and pushes the
// subtree back to the operand stack.
private void buildNewSubtree(InnerNode op)
{
// take op2, build new subtree and push to operand stack
Object topOperand = operandStack.Pop();
// can be LeafNode or MathTree (subtree)
if (topOperand is LeafNode)
{
LeafNode leafNode1 = (LeafNode)topOperand;
if (op.numArgs() == 2) // binary operator
{
Object nextOperand = operandStack.Pop();
if (nextOperand is LeafNode)
{
LeafNode leafNode2 = (LeafNode)nextOperand;
MathTree newSubtree = this.joinTrees(op, leafNode1, leafNode2);
operandStack.Push(newSubtree);
}
else
{
MathTree subtree2 = (MathTree)nextOperand;
MathTree newSubtree = this.joinTrees(op, leafNode1, subtree2);
operandStack.Push(newSubtree);
}
}
else // unary operator
{
MathTree newSubtree = this.joinTrees(op, leafNode1);
operandStack.Push(newSubtree);
}
}
else
{
MathTree subtree1 = (MathTree)topOperand;
if (op.numArgs() == 2) // binary operator
{
Object nextOperand = operandStack.Pop();
if (nextOperand is LeafNode)
{
LeafNode leafNode2 = (LeafNode)nextOperand;
MathTree newSubtree = this.joinTrees(op, subtree1, leafNode2);
operandStack.Push(newSubtree);
}
else
{
MathTree subtree2 = (MathTree)nextOperand;
MathTree newSubtree = this.joinTrees(op, subtree1, subtree2);
operandStack.Push(newSubtree);
}
}
else // unary operator
{
MathTree newSubtree = this.joinTrees(op, subtree1);
operandStack.Push(newSubtree);
}
}
}
