java - 电话资费计算器

Question

我正在尝试制作一个电话资费计算器。但是我遇到了nullpointerexceptions。无法弄清楚他们从哪里来。帮助表示赞赏!

注意我确实有另一个类接受用户输入到列表中。但这正如预期的那样工作

  import java.util.ArrayList;
  import java.util.List;

public class TariffCalc {

public void calculator(List<Integer> tariff){

    int whattariff = 0;
    int mins = 0;
    int texts = 0;
    int surchargeMin = 0;
    int surchargeText = 0;
    int totalsurcharge= 0;

    for( Integer s: tariff ){
        whattariff = tariff.get(0);
        mins = tariff.get(1);
        texts = tariff.get(2);
    }

 if ( whattariff == 1 && mins <= 200 && texts <= 150 ){
     System.out.println("Tariff 1: Within Allowance: £20 per month: Mins used: " + mins + " Texts used: " + texts );
 }
 else if( whattariff == 1 && mins > 200 ){
     surchargeMin = mins - 200;
     surchargeMin = (int) (surchargeMin * 0.1);
 }

 if ( whattariff == 1 && texts > 150 ){
     surchargeText = texts - 150;
     surchargeText = (int) (surchargeText * 0.05);
 }



 if ( whattariff == 2 && mins <= 400 && texts <= 350 ){
     System.out.println("Tariff 2: Within Allowance: £35 per month");
 }
 else if ( whattariff == 2 && mins > 400 ){
     surchargeMin = mins - 400;
     surchargeMin = (int) (surchargeMin * 0.1);
 }

 if ( whattariff == 2 && texts > 350 ){
     surchargeText = texts - 350;
     surchargeText = (int) (surchargeText * 0.05);
 }

 totalsurcharge = surchargeMin + surchargeText;

 if( whattariff == 1)
 System.out.println("Tariff 1: Allowance 200mins + 150 text. Used: " + mins + " + " + texts + ": Total Cost is £" + (20 + totalsurcharge) );
 else if (whattariff == 2){
     System.out.println("Tariff 2: Allowance 400mins + 350 text. Used: " + mins + " + " + texts + ": Total Cost is £" + (35 + totalsurcharge) );
 }

}
public static void main(String[] args) {


    TariffCalc c = new TariffCalc();
    c.calculator(null);

}

}

Answer 1

您在此行中传递一个 null 对象:

c.calculator(null);

并且您尝试在这一行中进行迭代

for( Integer s: tariff )

这会让你的代码抛出异常。

你应该这样做:

List<Integer> tariffs = new ArrayList<Integer>();
tariffs.add(1);
tariffs.add(2);
tariffs.add(3);
c.calculator(tariffs);

这给了我输出:

Tariff 1: Within Allowance: £20 per month: Mins used: 2 Texts used: 3
Tariff 1: Allowance 200mins + 150 text. Used: 2 + 3: Total Cost is £20