130242014056 王钰鹏 第2次实验

import java.util.*;

/**
 * Created by hasee on 2017/10/28.
 */
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while(true){
            System.out.print("calc > ");
            String text = scanner.nextLine();
            if (interpreter(text))
                System.out.println(calculate(lexer(text)));
            else
                System.out.println("输入有误，请重新输入！！");
        }

    }

    /*
    去除空字符串并将插入到队列中
     */
    public static List<Object> lexer(String s) {
        Map<String, Integer> map = new HashMap<String, Integer>();
        map.put("+", 0);
        map.put("-", 0);
        map.put("*", 1);
        map.put("/", 1);
        List<Object> list = new ArrayList<Object>();
        s = s.replace(" ", "");
        String[] number = s.split("[^\\d]");
        String[] operator = s.split("\\d+");
        Stack<String> stack = new Stack<String>();
        for (int i = 0; i < number.length; i++) {
            if (operator[i].length() != 0) {
                while (!stack.isEmpty()
                        && map.get(operator[i]) <= map.get(stack.peek())) {
                    list.add(stack.pop());
                }
                stack.push(operator[i]);
            }
            list.add(Double.parseDouble(number[i]));
        }
        while (!stack.isEmpty()) {
            list.add(stack.pop());
        }
        return list;
    }

    /**
     * 計算
     * @param list
     * @return
     */
    public static double calculate(List<Object> list) {
        Stack<Double> stack = new Stack<Double>();
        for (Object obj : list) {
            if (obj instanceof Double) {
                stack.push((Double) obj);
            } else {
                double b = stack.pop();
                double a = stack.pop();
                if (obj.equals("-"))
                    stack.push(a - b);
                if (obj.equals("*"))
                    stack.push(a * b);
                if (obj.equals("/"))
                    stack.push(a / b);
                if (obj.equals("+"))
                    stack.push(a + b);

            }
        }
        return stack.pop();
    }

    /**
     * 语法分析
     * @param text
     * @return
     */
    private static boolean interpreter(String text) {

        String[] signs = {"+", "-", "*", "/"};
        boolean isRight = true;

        boolean haveSign = false;
        for (String sign : signs) {

            if (text.contains(sign)) {
                haveSign = true;
            }

            if (text.contains(sign + sign)) {
                isRight = false;
            }

            if ( text.indexOf(sign) == 0 || text.lastIndexOf(sign) == text.length() - 1) {
                isRight = false;
            }
        }
        isRight = isRight && haveSign;
        return isRight;
    }
}