如果数组中不包含字符串，如何返回特定值

Question

I've written a program in which there are two arrays. One is an array of strings which contains the names of cities, and another contains the distances between each one. A method is run which returns the total distance between the two cities in the method call. However, if one or both of the cities are not contained in the array, I want the program to return the value -1, but I can't figure out how to do it. This is for a school assignment, and we have only covered up to creating our own methods, so I have to actually work this through using loops and if statements, and can't just write in a command to immediately check if the value is in the array.

import java.util.Scanner;
public class Q3{
   public static void main(String[] args){
      Scanner kbd = new Scanner(System.in);
      String[] towns = {"Halifax", "Enfield", "Elmsdale", "Truro", "Springfield", "Sackville", "Moncton"};
      int[] distances = {25, 5, 75, 40, 145, 55, 0};
      System.out.println("The distance between the two towns is " + distance(towns, distances, "Truro", "Moncton"));
   }
   public static int distance(String[] towns, int[] distances, String x, String y){
      int totdistance=0;//define total distance
      int j = 0;
      int k = 0;
      for(int i=0;i<towns.length;i++){//define variable j
         if (x.equals(towns[i])){
            j=i;
         }
      }
      for(int i=0;i<towns.length;i++){//define variable k
         if (y.equals(towns[i])){
            k=i;
         }
      }
      if (!y.equals(towns[k])){
         totdistance=-1;
      }
      if (j<k&&j!=-1){//if j less than k calculate distance
        for(;j<k;j++){
               totdistance+=distances[j];
         }
      }
      else if (k<j&&k!=-1){//if k less than j calculate distance
         for(;k<j;k++){
            totdistance+=distances[k];
         }
      }
      return totdistance;
   }
}

Answer 1

You should give the variables j and k the initial value -1 . If x or y is not in the array, j or k will still be -1 after the loop, so you can return -1 .

int j = -1;
int k = -1;
for(int i=0;i<towns.length;i++){//define variable j
   if (x.equals(towns[i])){
      j=i;
   }
}
for(int i=0;i<towns.length;i++){//define variable k
   if (y.equals(towns[i])){
      k=i;
   }
}
if (j == -1 || k == -1)
    return -1;

Answer 2

You have to initialize k and j in your method to some index that is not an array index eg (-1) Then check whether any of them are equal to their initial value after the first two loops. Here is a modified code that will return -1 if one or both of the cities are not found in the array:

import java.util.Scanner;
public class Q3{
   public static void main(String[] args){
      Scanner kbd = new Scanner(System.in);
      String[] towns = {"Halifax", "Enfield", "Elmsdale", "Truro", "Springfield", "Sackville", "Moncton"};
      int[] distances = {25, 5, 75, 40, 145, 55, 0};
      System.out.println("The distance between the two towns is " + distance(towns, distances, "Truro1", "Moncton1"));
   }
   public static int distance(String[] towns, int[] distances, String x, String y){
      int totdistance=0;//define total distance
      int j = -1;
      int k = -1;
      for(int i=0;i<towns.length;i++){//define variable j
         if (x.equals(towns[i])){
            j=i;
         }
      }
      for(int i=0;i<towns.length;i++){//define variable k
         if (y.equals(towns[i])){
            k=i;
         }
      }

      if(k==-1||j==-1){
          return -1;
      }

      if (!y.equals(towns[k])){
         totdistance=-1;
      }
      if (j<k&&j!=-1){//if j less than k calculate distance
        for(;j<k;j++){
               totdistance+=distances[j];
         }
      }
      else if (k<j&&k!=-1){//if k less than j calculate distance
         for(;k<j;k++){
            totdistance+=distances[k];
         }
      }
      return totdistance;
   }
}