java - 将 CSV 文件解析为 HashMap 存储空值

Question

我正在尝试读取 csv 文件并将数据存储到 HashMap 中。我能够正确添加键，但是在添加值时，它会为每个值添加 null 。我不知道为什么。这是我的代码:

编辑代码:

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.*;

public class ExampleActivity {
    public static HashMap<String, String> hm = new HashMap<String, String>();

    public static void readCountry() throws IOException{
        BufferedReader reader = new BufferedReader(new FileReader("countries.csv"));    
        String line;
        HashMap<String, String> hm = new HashMap<String, String>();

        while ((line = reader.readLine()) != null) {
            String str[] = line.split(",");
            if (str.length > 1) {
                System.out.println("Data 0: " + str[0]);
                System.out.println("Data 1: " + str[1]);
                hm.put(str[0].trim(), str[1]);
            }

        }
        //System.out.println(hm);
    }

    public static void main(String[] args) throws IOException {

        readCountry();

        Scanner in = new Scanner(System.in);
        String l = null;

        System.out.println("Please enter a three letter country:");
        l = in.nextLine();
        l = l.trim();
        // System.out.println("Country Code: " + l + "\nCountry Name: " +
        // hm.get(l) );
        if (hm.containsKey(l)) {
            System.out.println("Country Code: " + l + "\nCountry Name: "
                + hm.get(l));
        } else {
            System.out.println("Missing key for " + l);
        }
    }
}

这是 CSV 文件的示例

AFG,Afghanistan
AGO,Angola
AIA,Anguilla
...

这是输出的屏幕截图:

Answer 1

注释掉 hashmap 的方法本地声明，它应该可以正常工作。修改代码如下:

public static void readCountry() throws IOException{

    BufferedReader reader = new BufferedReader(new FileReader("d:/countries1.csv")); 
    String line;
  //  HashMap<String, String> hm = new HashMap<String, String>(); Remove this line