使用传入的参数作为我的计算器的 inputString 执行计算

Question

如果我运行我的计算器，我希望它开始使用给定的参数自动计算，例如4+4-2。当没有参数时，他只是要求用户插入数字（扫描仪）。这是我的 code.So args 需要分配给我的 inputString 如果没有 args 扫描器将要求用户插入一些东西。

主要

package com.haynespro.calculator;

import java.util.Scanner;

public class CharAtExample {

public static void main(String[] args) {

    for (String arg : args) {

        System.out.println(arg);


    }

    // inputString with scanner

    String inputString = "0";

    inputString = inputString.replace(",", "");

    Scanner userInput = new Scanner(System.in);

    System.out.print("please insert your calculations: ");

    inputString = userInput.next();

    userInput.close();

    Calculator calculator = new Calculator();

    calculator.startCalculator(inputString);

  }// end of main
}// end of class

计算器

package com.haynespro.calculator;

import java.util.ArrayList;

public class Calculator {

 public void startCalculator(String inputString) {

    // Assign ArrayList of Strings "res" to splitExpression

    ArrayList<String> res = splitExpression(inputString);

    // Create an ObjectList that holds res

    ArrayList<Object> objectList = new ArrayList<Object>(res);

    System.out.print("\nLet my algorithm take care of it: \n\n");

    // Loop through the objectList and convert strings to doubles

    for (int i = 0; i < objectList.size(); i++) {
        try {
            objectList.set(i, Double.parseDouble((String) 
  objectList.get(i)));
        } catch (NumberFormatException nfe) {

        }
    }

    // Create a variable maxi to substract 2 from the objectList index

    int maxi = objectList.size();

    maxi = maxi - 2;

    // Create variable lastSum out of the incoming for-loop's scope.

    double lastSum = 0;

    // Loop through the objectList with an algorhitm and perform 
    calculations with
    // invoking the sum method

    for (int i = 0; i < maxi; i += 2) {
        String operator = (String) objectList.get(i + 1);
        double a = (Double) objectList.get(i);
        double b = (Double) objectList.get(i + 2);
        double sum;

        if (i == 0) {
            sum = sum(a, b, operator);
        } else {
            sum = sum(lastSum, b, operator);
        }
        lastSum = sum;
        System.out.println(lastSum);
    }

}

// Method that matches the string input with operators to perform 
calculations.

public static double sum(Double a, Double b, String operator) {

    if (operator.equals("+")) {
        return a + b;
    }
    if (operator.equals("-")) {
        return a - b;
    }
    if (operator.equals("*")) {
        return a * b;
    }
    if (operator.equals("/")) {
        return a / b;
    }
    return 0;
}

// ArrayList splitExpression that casts to inputString

private static ArrayList<String> splitExpression(String inputString) {

    // ArrayList result to return the result

    ArrayList<String> result = new ArrayList<String>();

    // Uses the toCharArray method to insert the string reference per 
  character into
    // an array

    char[] destArray = inputString.toCharArray();

    // Empty String created

    String token = "";

    // Iterate through the "Items" in the Array

    for (int i = 0; i < destArray.length; i++) {

        // Nice all those references but we need an Object that actually 
 holds the array

        char c = destArray[i];

        // If not a number then add to token, else assign the value of c to 
 token

        if (isBreakCharacter(c)) {
            result.add(token);
            result.add(Character.toString(c));
            token = "";
        } else
            token = token + c;

    }

    result.add(token);
    return result;
}

// a method that breaks characters which are not numbers.The object "c" also
// needs to hold this method.

public static boolean isBreakCharacter(char c) {
    return c == '+' || c == '*' || c == '-' || c == '/';
}

}

Answer 1

您没有验证 args.length 来计算传入了多少参数。

我会给你一个简化的版本，因为我不知道你应该如何 read/parse args。

String input;

if (args.length < 1) {
    // you need a Scanner to read an input for the calculator
    input = new Scanner(System.in).nextLine();
} else {
    // you've got args to parse
    input = String.join("", args);
}

new Calculator().startCalculator(input);

Answer 2

使用 args 改变你的 main（也在 main class 中进行一些重构）：

public static void main(String[] args) {
    String input=null;
    if(args.length>0){
        input=args[0];
        System.out.println(input);
    }else{
        input=askForInput();
    }

    Calculator calculator = new Calculator();

    calculator.startCalculator(input);

}// end of main

private static String askForInput() {
    // inputString with scanner
    Scanner userInput = new Scanner(System.in);
    System.out.print("please insert your calculations: ");
    String inputString;
    try {
        inputString = userInput.next();
    } finally {
        userInput.close();
    }
    return inputString;
}

使用传入的参数作为我的计算器的 inputString 执行计算

perform calculations with incoming args as my inputString for my calculator

java

args