java - 数组返回为空而不是数字列表

Question

基本上，我正在为我的类(class)开发一个程序，从文本文件中查找数字的前导数字并对它们进行排序。我知道我没有最好的编码技能，因为我是初学者，但我知道如何做到这一点。不知何故，我遇到了一个问题，即应该返回的数组为空。实际上，这个数组返回了两次。第一次，到 main 方法，它返回整齐，但是当它返回到 change3() 时，它返回“[].”

我尝试更改周围的变量，甚至尝试组合这些方法，但没有任何效果，我只是收到错误。

import java.io.*;
import java.util.*;

class PG 
{
    public static void main(String[] args)
    {   
        List<String> Strings = new ArrayList<String>();
        Strings = change(); // it works perfectly right here
        System.out.println(Strings); // it works perfectly right here
        List<Integer> Integers = new ArrayList<Integer>();
        Integers = change2();
        List<Integer> leads = new ArrayList<Integer>();
        leads = change3();
    }


    public static List<String> change()
    {
        Scanner in = new Scanner(System.in);
        List<String> list_S = new ArrayList<String>();
        while (in.hasNextLine()) 
        {
                String line = in.nextLine();
                line = line.replaceAll(",", "");
                int result = Integer.parseInt(line);
                List<Integer> list_I = new ArrayList<Integer>();
                list_I.add(result);
                list_S.add(line);
        }
        return list_S;
    }

    public static List<Integer> change2()
    {
        Scanner in = new Scanner(System.in);
        List<Integer> list_I = new ArrayList<Integer>();
        while (in.hasNextLine()) 
        {
                String line = in.nextLine();
                line = line.replaceAll(",", "");
                int result = Integer.parseInt(line);
                List<String> list_S = new ArrayList<String>();
                list_I.add(result);
                list_S.add(line);
        }
        return list_I;

    }

    public static List<Integer> change3()
    {
        List<String> list = new ArrayList<String>();
        list = change();  // This is supposed to give me a list of numbers(string) so it can help me find the leading digit
        System.out.println(list); // checking to see if the list even has numbers in it.  It does not.  It returns [] as if nothing is in the list.
        List<Integer> leads = new ArrayList<Integer>();
        for (int i = 0; i < list.size(); i++)
        {
            // get the leading integer
        }
        return leads;
    }
}

基本上，现在我只希望它在 change3() 方法中打印列表，这样我就可以继续处理该程序。

Answer 1

试试这个代码。它应该有效。如果它不起作用，请评论该问题。

也将此代码与您的相匹配。

更改方法有一些变化。我已经删除了多余的代码。

如果使用相同的列表，我建议在所有 3 个更改方法中传递该列表。这样您就不必借助扫描仪再次阅读它。

import java.io.*;
import java.util.*;

class PG 
{
    public static void main(String[] args)
    {   
        List<String> Strings = new ArrayList<String>();
        Strings = change(); // it works perfectly right here
        System.out.println(Strings); // it works perfectly right here
        List<Integer> Integers = new ArrayList<Integer>();
        Integers = change2();
        List<Integer> leads = new ArrayList<Integer>();
        leads = change3();
    }


    public static List<String> change()
    {
        Scanner in = new Scanner(System.in);
        List<String> list_S = new ArrayList<String>();
        while (in.hasNextLine()) 
        {
                String line = in.nextLine();
                line = line.replaceAll(",", "");
                list_S.add(line);
        }
        return list_S;
    }

    public static List<Integer> change2()
    {
        Scanner in = new Scanner(System.in);
        List<Integer> list_I = new ArrayList<Integer>();
        while (in.hasNextLine()) 
        {
                String line = in.nextLine();
                line = line.replaceAll(",", "");
                int result = Integer.parseInt(line);
                list_I.add(result);
        }
        return list_I;

    }

    public static List<Integer> change3()
    {
        List<String> list = new ArrayList<String>();
        list = change();  // This is supposed to give me a list of numbers(string) so it can help me find the leading digit
        System.out.println(list); // checking to see if the list even has numbers in it.  It does not.  It returns [] as if nothing is in the list.
        List<Integer> leads = new ArrayList<Integer>();
        for (int i = 0; i < list.size(); i++)
        {
            // get the leading integer
        }
        return leads;
    }
}