InfixExpr.java

package com.pan.stack.expr;

import java.util.List;
import java.util.Stack;


public class InfixExpr {
    String expr = null;

    public InfixExpr(String expr) {
        this.expr = expr;
    }

    public float evaluate() {


        TokenParser parser = new TokenParser();
        List<Token> tokens = parser.parse(this.expr);


        Stack<Token> opStack = new Stack<>();
        Stack<Float> numStack = new Stack<>();

        for (Token token : tokens) {

            if (token.isOperator()) {

                while (!opStack.isEmpty()
                        && !token.hasHigherPriority(opStack.peek())) {
                    Token prevOperator = opStack.pop();
                    Float f2 = numStack.pop();
                    Float f1 = numStack.pop();
                    Float result = CalculateUtil.calculate(prevOperator.toString(), f1, f2);
                    numStack.push(result);

                }
                opStack.push(token);
            }
            if (token.isNumber()) {
                numStack.push(new Float(token.getIntValue()));
            }
        }

        while (!opStack.isEmpty()) {
            Token token = opStack.pop();
            Float f2 = numStack.pop();
            Float f1 = numStack.pop();
            numStack.push(CalculateUtil.calculate(token.toString(), f1, f2));
        }


        return numStack.pop().floatValue();
    }


}