java 解析字符串表达式

package cn.jiangzeyin.util.util;

import java.util.ArrayList;
import java.util.Objects;
import java.util.Stack;

/**
 * Created by jiangzeyin on 2017/6/14.
 */
public class Calculate {

    /**
     * 将字符串转化成List
     *
     * @param str str
     * @return array
     */
    public static ArrayList
 
   getStringList(String str) {
        ArrayList
  
    result = new ArrayList<>(); StringBuilder num = new StringBuilder(); for (int i = 0; i < str.length(); i++) { if (Character.isDigit(str.charAt(i))) { num.append(str.charAt(i)); } else { if (!Objects.equals(num.toString(), "")) { result.add(num.toString()); } result.add(str.charAt(i) + ""); num = new StringBuilder(); } } if (!Objects.equals(num.toString(), "")) { result.add(num.toString()); } return result; } /** * 将中缀表达式转化为后缀表达式 * * @param inOrderList list * @return array */ public static ArrayList
   
     getPostOrder(ArrayList
    
      inOrderList) { ArrayList
     
       result = new ArrayList<>(); Stack
      
        stack = new Stack<>(); for (String anInOrderList : inOrderList) { if (Character.isDigit(anInOrderList.charAt(0))) { result.add(anInOrderList); } else { switch (anInOrderList.charAt(0)) { case '(': stack.push(anInOrderList); break; case ')': while (!stack.peek().equals("(")) { result.add(stack.pop()); } stack.pop(); break; default: while (!stack.isEmpty() && compare(stack.peek(), anInOrderList)) { result.add(stack.pop()); } stack.push(anInOrderList); break; } } } while (!stack.isEmpty()) { result.add(stack.pop()); } return result; } /** * 计算后缀表达式 * * @param postOrder post * @return int */ public static Integer calculate(ArrayList
       
         postOrder) { Stack
        
          stack = new Stack<>(); for (String aPostOrder : postOrder) { if (Character.isDigit(aPostOrder.charAt(0))) { stack.push(Integer.parseInt(aPostOrder)); } else { Integer back = stack.pop(); Integer front = stack.pop(); Integer res = 0; switch (aPostOrder.charAt(0)) { case '+': res = front + back; break; case '-': res = front - back; break; case '*': res = front * back; break; case '/': res = front / back; break; } stack.push(res); } } return stack.pop(); } /** * 比较运算符等级 * * @param peek peek * @param cur cur * @return boolean */ public static boolean compare(String peek, String cur) { if ("*".equals(peek) && ("/".equals(cur) || "*".equals(cur) || "+".equals(cur) || "-".equals(cur))) { return true; } else if ("/".equals(peek) && ("/".equals(cur) || "*".equals(cur) || "+".equals(cur) || "-".equals(cur))) { return true; } else if ("+".equals(peek) && ("+".equals(cur) || "-".equals(cur))) { return true; } else if ("-".equals(peek) && ("+".equals(cur) || "-".equals(cur))) { return true; } return false; } public static int calculate(String s) { ArrayList result = getStringList(s); //String转换为List result = getPostOrder(result); //中缀变后缀 return calculate(result); //计算 } public static void main(String[] args) { Calculate calculate = new Calculate(); String s = "12+(23*3-56+7)*(2+90)/2"; ArrayList result = calculate.getStringList(s); //String转换为List result = calculate.getPostOrder(result); //中缀变后缀 int i = calculate.calculate(result); //计算 System.out.println(i); } }