EquationNode.~ava

public class EquationNode {
  private byte state; //0:IsNumber, 1:IsVariable, 2:IsOperator, 3:IsSpecialFunc;
  private Object value;
  public EquationNode left;
  public EquationNode right;
  
  public EquationNode(byte state, String value) {
    this.state = state;
    this.value = value;
  }
  
  public EquationNode(byte state, double value) {
    this.state = state;
    this.value = value;
  }

  public double calculate(double x, double y, Variable[] parameters) {
    if (state == 0) {
      return (double) value;
    } else if (state == 1) {
        String varName = (String) value;
        if (varName.equals("x")) {
          return x;
        } else if (varName.equals("y")) {
            return y;
          } else {
            return readVar(parameters, varName);
          }
      } else if (state == 2 && left != null && right != null) {
          double part1 = left.calculate (x,y,parameters);
          double part2 = right.calculate (x,y,parameters);
          String op = (String) value;
          if (op.equals("+")) {
            return part1 + part2;
          }
            else if (op.equals("-")) {
              return part1 - part2;
            }
              else if (op.equals("*")) {
                return part1 * part2;
              }
                else if (op.equals("/")) {
                  return part1 / part2;
                }
                  else if (op.equals("^")) {
                    return Math.pow(part1,part2);
                  }
                    else  if (op.equals("root")) {
                      return Math.pow(part2, 1.0 / part1);
                    }
                      else  if (op.equals("log")) {
                        return Math.log(part2) / Math.log(part1);
                      }
                      else {
                        System.out.println("Invalid Operator!");
                      }
        } else if(state == 3 && left != null) {
            String op = (String) value;
            double calVal = left.calculate(x,y,parameters);
            if (op.equals("sin")) {
              return Math.sin(calVal);
            } else if (op.equals("cos")) {
                return Math.cos(calVal);
              } else if (op.equals("tan")) {
                  return Math.tan(calVal);
                } else if (op.equals("ln")) {
                    return Math.log(calVal);
                  } else {
                    System.out.println("Invalid special function!");
                  }
          } else {
            System.out.println("Invalid Node!");
          }
    return 0.0;
  }

  private static double readVar(Variable[] parameters, String varName) {
    for (int i = 0; i< parameters.length; i++) {
      if (parameters[i].name.equals(varName)) {
        return parameters[i].value;
      }
    }
    System.out.println("Error: Invalid Parameter!");
    return 0;
  }

}