public class ExprNode {
  String operator;
  ExprNode left;
  ExprNode right;
  double value;

  public ExprNode(String op) {
    operator = op; 
    left = null;
    right = null;
    value = 0;
  }

  public String getOperator() {
    return operator;
  }

  public ExprNode getLeft() {
    return left;
  }

  public ExprNode getRight() {
    return right;
  }

  public double getValue() {
    return value;
  }

  public void setOperator(String op) {
    operator = op;
  }

  public void setLeft(ExprNode node) {
    left = node;
  }

  public void setRight(ExprNode node) {
    right = node;
  }

  public void setValue(double val) {
    value = val;
  }

  public double eval() {
    if (operator.equals("int"))
      return value;
    else if (operator.equals("+"))
      return left.eval() + right.eval();
    else if (operator.equals("-"))
      return left.eval() - right.eval();
    else if (operator.equals("*"))
      return left.eval() * right.eval();
    else // must be DIV
      return left.eval() / right.eval();
  }

}