Infix expression is transformed into postfix expression, optimized version 1

package org.structure.stack;

import java.util.ArrayList;
import java.util.Stack;
/**
 * 中缀表达式转化成后缀表达式的过程
 * @author cjj_1
 * @date 2020-08-07 15:05
 */
public class ToSuffix {
    
    
    public static void main(String[] args) {
    
    
        Stack<String> s1= new Stack<String>(); //数栈
        Stack<String> s2= new Stack<String>();//操作符栈
        String expression  = "5 + 6 * ( 9 - 8 + 7 ) - 2";
        String[] suffixArr = expression.split(" ");
        ArrayList<String> list = new ArrayList<String>();
        int num1;
        int num2;
        String oper;
        int res ;
        //将数组转换成 list
        for(int i =0 ;i< suffixArr.length;i++){
    
    
            list.add(suffixArr[i]);
        }
        //开始遍历表达式
        for(int i =0;i<list.size();i++){
    
    
            String item = list.get(i);
            if(item.matches("\\d+"))//如果是数字直接入栈是s1
                s1.push(item);
            else if(!isOper(item)) {
    
    //如果是非法字符抛出异常
                throw new RuntimeException(item + ":是非法字符");
            }else if (item.equals(")")){
    
    //如果是右括号，遍历s2中的字符，直到栈顶元素是左括号为止
                while (!s2.peek().equals("(")){
    
    
                        oper = s2.pop();
                        s1.push(oper);
                }
                s2.pop();//栈顶元素是左括号，出栈
                continue;
            }else if(s2.empty()|| item.equals("(")||priority(item)>priority(s2.peek())){
    
    
                s2.push(item);//当s2为空，或者是左括号，或者是栈顶元素的优先级小于当前操作符，入s2
            }else if(priority(item)<=priority(s2.peek())){
    
    
                oper = s2.pop();
                s1.push(oper);
                while (!s2.isEmpty() && priority(item)<=priority(s2.peek())){
    
    
                    oper = s2.pop();
                    s1.push(oper);
                }
                s2.push(item);
            }
        }
        //清空s2中的操作符
        while (!s2.isEmpty()){
    
    
            s1.push(s2.pop());
        }
        //打印出后缀表达式
        s1.forEach(s->{
    
    
            System.out.print(s+" ");
        });
        System.out.println(";");
        //输出结果为：5,6,9,7,-,*,2,-,+, 是我们的后缀表达式

    }

    /**
     * 运算数据
     * @param num1
     * @param num2
     * @param oper
     * @return
     */
    public static int calcalator(int num1,int num2,String oper){
    
    
        int res=0;
        switch (oper){
    
    
            case "*":
                res = num2*num1;
                break;
            case "/":
                res = num2/num1;
                break;
            case "+":
                res = num2+num1;
                break;
            case "-":
                res = num2-num1;
                break;
            default:
                res=-1;
                break;
        }

        return  res;

    }

    /*
     * 比较操作符的优先级
     * @author cjj_1
     * @date 2020-08-06 11:50:31
     * @param oper
     * @return
     **/
    public static int priority(String oper){
    
    
        if(oper.equals("*") || oper.equals("/"))
            return 1;
        else if(oper.equals("+") || oper.equals("-"))
            return 0;
        else
            return  -1;
    }
    //是否是操作符
    public static  boolean isOper(String oper){
    
    
        if(oper.equals("+")||oper.equals("-")||oper.equals("*")||oper.equals("/")||oper.equals("(")||oper.equals(")"))
            return Boolean.TRUE;
        return Boolean.FALSE;
    }
    //是否是左括号
    public static  boolean isLeftBracket(String oper){
    
    
        if(oper.equals("("))
            return Boolean.TRUE;
        return Boolean.FALSE;
    }
    //是否是右括号
    public static  boolean isRightBracket(String oper){
    
    
        if(oper.equals(")"))
            return Boolean.TRUE;
        return Boolean.FALSE;
    }
}