Question

我正在使用while循环创建一个数组。（由于我以这种方式创建数组的原因，请转到https://www.cia.gov/library/publications/the-world-factbook/rankorder/rawdata_2151.txt）虽然我的数组（data）是在while循环内创建的，但我无法在while循环之外访问它。我希望这样做，以便用户可以输入一个国家的名称，比如印度，并获得该国家的移动用户数量。

String address = "https://www.cia.gov/library/publications/the-world-factbook/rankorder/rawdata_2151.txt";
URL pageLocation = new URL(address);
Scanner in1 = new Scanner(pageLocation.openStream());
Scanner in = new Scanner(System.in);
String line;
System.out.print("Please enter the name of the country you would like to see the mobile users for: ");
String country = in.next();
 while (in1.hasNextLine()){
 line = in1.nextLine();
 String[] data = line.split("\t");
 if (data[1].contains(country) == true){
   System.out.println("Country name: " + data[1]);
   System.out.println("Mobile phone subscribers: " + data[2]);
   return;
 } 
 else{
   System.out.println("No country found with that name!");
   return;
    }
  }

如果输入在循环内部，则输入有效，但仅适用于中国，因为它是列表中的第一个国家/地区。我理解为什么它不能正常工作，以为我不确定如何修复它除了将if语句放在循环之外，但如果我这样做，语句就无法到达我的数组。有什么建议吗？

Answer 1

问题在于：

 if (data[1].contains(country) == true){
   System.out.println("Country name: " + data[1]);
   System.out.println("Mobile phone subscribers: " + data[2]);
   return;
 } else {
   System.out.println("No country found with that name!");
   return; //<-----ISSUE
 }

在else子句中调用return时，它会终止程序。它真正需要做的是迭代循环的第二次运行。

删除return中的else-statment。

以下是修订后的代码：

import java.io.IOException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Scanner;

public class TestClass {
    public static void main(String[] args) throws IOException {
        String address = "https://www.cia.gov/library/publications/the-world-factbook/rankorder/rawdata_2151.txt";
        URL pageLocation = new URL(address);
        Scanner in1 = new Scanner(pageLocation.openStream());
        Scanner in = new Scanner(System.in);
        String line;
        System.out
                .print("Please enter the name of the country you would like to see the mobile users for: ");
        String country = in.next();

        while (in1.hasNextLine()) {
            line = in1.nextLine();
            String[] data = line.split("\t");

            if (data[1].contains(country) == true) {
                System.out.println("Country name: " + data[1]);
                System.out.println("Mobile phone subscribers: " + data[2]);
                return; //<--- will exit after printing ^
            }
        }
        System.out.println("No country found with that name!");
    }
}

以下是一个示例运行：{input} India

Please enter the name of the country you would like to see the mobile users for: India
Country name: India
Mobile phone subscribers:       893,862,000

Answer 2

您无法迭代到第二行，因为您在第一次迭代后返回，无论是否找到该国家/地区。

我建议从else条件中删除return语句。

我还使用了boolean找到的变量，该变量将在找到国家/地区后设置，只有当该国家/地区不在列表中时才会显示No country found消息。

import java.io.IOException;
import java.net.URL;
import java.util.Scanner;

public class CountryName {
public static void main(final String[] args) throws IOException {
    final String address = "https://www.cia.gov/library/publications/the-world-factbook/rankorder/rawdata_2151.txt";
    final URL pageLocation = new URL(address);
    final Scanner in1 = new Scanner(pageLocation.openStream());
    final Scanner in = new Scanner(System.in);
    boolean found = false;
    String line;
    System.out
            .print("Please enter the name of the country you would like to see the mobile users for: ");
    final String country = in.next();
    while (in1.hasNextLine()) {
        line = in1.nextLine();
        final String[] data = line.split("\t");
        if (data[1].contains(country) == true) {
            System.out.println("Country name: " + data[1]);
            System.out.println("Mobile phone subscribers: " + data[2]);
            found = true;
            return;
        }
    }
    if (!found) {
        System.out.println("No Country Found");
    }
in.close();
in1.close();
}

}

另一方面，如果您想使用集合，您的程序将变得更简洁易读。这与HashMap

的逻辑相同

import java.io.IOException;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;
public class CountryName {
    public static void main(final String[] args) throws IOException {
        final String address = "https://www.cia.gov/library/publications/the-world-factbook/rankorder/rawdata_2151.txt";
        final URL pageLocation = new URL(address);
        final Scanner in1 = new Scanner(pageLocation.openStream());
        final Scanner in = new Scanner(System.in);
        final Map<String, String> countryMap = new HashMap<String, String>();
        while (in1.hasNextLine()) {
            final String[] line = in1.nextLine().split("\t");
            countryMap.put(line[1], line[2]);
        }
        System.out.print("Please enter the name of the country you would like to see the mobile users for: ");
        final String country = in.next();
        if (countryMap.containsKey(country)) {
            System.out.println("Country Name: " + country);
            System.out.println("Mobile phone subscribers: "+ countryMap.get(country));
        } else {
            System.out.println("No Country found with that name");
        }
        in.close();
        in1.close();
    }
}

Answer 3

尝试放

String[] data;

在循环之前

。这将使其范围大于循环。

Answer 4

在＆＃34;之外宣布数据，而＃34;但是把它分配到里面。

String address = "https://www.cia.gov/library/publications/the-world-        factbook/rankorder/rawdata_2151.txt";
URL pageLocation = new URL(address);
Scanner in1 = new Scanner(pageLocation.openStream());
Scanner in = new Scanner(System.in);
String line;
System.out.print("Please enter the name of the country you would like to see the mobile users for: ");
String country = in.next();
String[] data; 
while (in1.hasNextLine()){
   line = in1.nextLine();
   data = line.split("\t");
   if (data[1].contains(country) == true){
     System.out.println("Country name: " + data[1]);
     System.out.println("Mobile phone subscribers: " + data[2]);
     return;
   } else{
   System.out.println("No country found with that name!");
   return;
   }
 }
Objects.toString(data); // now its visible

在循环外部访问while循环创建的数组

4 个答案: