子程序服用數組作爲參數在Java中

Question

在下面的程序中，假設用戶輸入String（一個城市的名稱）和節目應該返回相應城市的索引在數組中。

但我得到一個錯誤，在子程序indexCities以下消息：

「nameCity解決不了」。

我想這是一個變量範圍界定的問題，但我不知道該怎麼做。 感謝您的幫助。

import java.util.Scanner; 

public class villes { 

    public static void main(String[] args) { 
     String cities[] = {"Vierzon","Salbris","Nouans","LB","LFSA","Orleans"}; 
     Scanner input = new Scanner(System.in); 
     String nameCity = input.nextLine(); 
     indexCities(cities); 
    } 

    public static int indexCities(String cities[]) { 
     for (int i = 0; i < cities.length; i++) { 
      if(nameCity.equals(cities[i])) { 
       System.out.println(i); 
       break; 
      } 
     } 
    } 

} 

Answer 1

nameCity是您的主要方法中的局部變量。您不能在方法外訪問它。 您的一個選擇是將nameCity也作爲indexCities方法中的參數傳遞。你的indexCities方法的返回類型應該是void，因爲你沒有返回任何東西。

public static void main(String[] args) { 

    String cities[] = {"Vierzon","Salbris","Nouans","LB","LFSA","Orleans"}; 

    Scanner input = new Scanner(System.in); 

    String nameCity = input.nextLine(); 

    indexCities(cities, nameCity); 

} 

public static void indexCities(String cities[], String nameCity){ 

    for (int i = 0; i < cities.length; i++) { 
     if(nameCity.equals(cities[i])) { 
      System.out.println(i); 
      break; 
     } 
    } 
} 

Answer 2

你可以做這樣：

public static void main(String[] args) { 
    String cities[] = { "Vierzon", "Salbris", "Nouans", "LB", "LFSA", "Orleans" }; 
    int index = indexCities(cities, "Vierzon"); 
    System.out.println("Index of city Vierzon is: " + index); 
} 

public static int indexCities(String cities[], String cityName) { 
    List<String> cityList = Arrays.asList(cities); 
    return cityList.indexOf(name); 
} 

Answer 3

變量nameCity的範圍僅限於主要功能。您不能在主功能之外訪問它。

Answer 4

變量超出範圍，當您嘗試使用它的方法indexCities內。一種解決方案是通過將變量的定義移出主方法來使變量nameCity成爲實例變量，但是您的代碼也可以通過多種方式進行改進。檢查下面的一些選項：

這將打印您正在尋找的陣列內的城市指數：

import java.util.Scanner; 

public class villes { 

    public static void main(String[] args) {  
    String cities[] = {"Vierzon","Salbris","Nouans","LB","LFSA","Orleans"}; 
    Scanner input = new Scanner(System.in); 
    String nameCity = input.nextLine(); 
    indexCities(nameCity, cities); 
    } 

    public static void indexCities(String copyOfNameCity, String cities[]){ 
    for (int i = 0; i < cities.length; i++) { 
     if(copyOfNameCity.equals(cities[i])) { 
     System.out.println(i); 
     break; 
     } 
    } 
    } 
} 

您可以通過使得該方法返回一個值改善。就像這樣：

import java.util.Scanner; 

public class villes { 

    public static void main(String[] args) {  
    String cities[] = {"Vierzon","Salbris","Nouans","LB","LFSA","Orleans"}; 
    Scanner input = new Scanner(System.in); 
    String nameCity = input.nextLine(); 
    int cityIndex = indexCities(nameCity, cities); 
     System.out.println(cityIndex == -1 ? "City not found" : "City found in index " + cityIndex);  
    } 

    public static int indexCities(String nameCity, String cities[]){ 
    for (int i = 0; i < cities.length; i++) { 
     if(nameCity.equals(cities[i])) { 
     return i; 
     } 
    } 
    return -1; 
    } 
} 

另一種方法是：

import java.util.Arrays; 
import java.util.List; 
import java.util.Scanner; 

public class test2 { 

    public static void main(String[] args) { 
     String cities[] = {"Vierzon", "Salbris", "Nouans", "LB", "LFSA", "Orleans"}; 
     Scanner input = new Scanner(System.in); 
     System.out.print("Enter the name of city to be searched -> "); 
     String nameCity = input.nextLine(); 
     int cityIndex = indexCities(nameCity, cities); 
     System.out.println(cityIndex == -1 ? "City not found" : "Found at position " + cityIndex); 
     input.close(); 
    } 

    public static int indexCities(String cityName, String cities[]) { 
     List<String> cityList = Arrays.asList(cities); 
     return cityList.indexOf(cityName); 
    } 
}