java - 通过从扫描仪中读取行来实例化一个 ArrayList，在哪里声明对象？

Question

我想用输入文件中的行填充数组列表，输入文件如下所示:

7f00000000000000000000000000000000000000000000000000000000000000027f00000000000000000000000000000000000000000000000000000000000000027f00000000000000000000000000000000000000000000000000000000000000020101
7f00000000000000000000000000000000000000000000000000000000000000037f00000000000000000000000000000000000000000000000000000000000000037f00000000000000000000000000000000000000000000000000000000000000030101
7f00000000000000000000000000000000000000000000000000000000000000047f00000000000000000000000000000000000000000000000000000000000000047f00000000000000000000000000000000000000000000000000000000000000040101
7f00000000000000000000000000000000000000000000000000000000000000057f00000000000000000000000000000000000000000000000000000000000000057f00000000000000000000000000000000000000000000000000000000000000050101
7f00000000000000000000000000000000000000000000000000000000000000067f00000000000000000000000000000000000000000000000000000000000000067f00000000000000000000000000000000000000000000000000000000000000060101

我想基于此创建的 Java 数据对象会将这些行中的每一行都作为一个新字符串，并且它们将一起存在于一个列表中，可以这么说*。

因此，在我尝试将文件的行读入此数组列表的不同部分时，我无法弄清楚我需要在主程序中的何处声明数组列表。我的计划是用单独的方法填充它:

import java.io.*;
import java.util.Scanner;
import java.util.List;
import java.util.Array;
import java.util.ArrayList;

class evmTest {

public static void main(String[] args) {


    Array<String> inputLinesObject = new ArrayList<String>();

    // populate from file
    inputLinesObject = readFile("/Users/s.matthew.english/codes.txt", inputLinesObject);


    System.out.println(Array.toString(inputLinesObject));

}

    private static void readFile(String fileName, Array<String> inputLines) {
        try {
            File file = new File(fileName);
            Scanner scanner = new Scanner(file);
            while (scanner.hasNextLine()) {
                // System.out.println(scanner.nextLine());
                inputLines.add(scanner.nextLine());
            }
            scanner.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
        return inputLines;
    }

}

也许我可以先将它实例化为null，然后将那个null 数组列表传递给要填充的方法？

* 最后一句话中的术语并不完全准确 - 请原谅我 - 我正在重新调整 Java 的词汇，但我认为我想做的事情应该足够清楚。如果不是，请告诉我，我很乐意澄清。

Answer 1

对于您的测试，您只需在 try 之上实例化 ArrayList

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class EvmTest {

    public static void main(final String[] args) {
        // populate from file
        final List<String> inputLinesObject = EvmTest.readFile("/Users/s.matthew.english/codes.txt");

        for (final String line : inputLinesObject) {
            System.out.println(line);
        }
    }

    private static List<String> readFile(final String fileName) {
        final List<String> inputLinesObject = new ArrayList<>();

        try {
            final File file = new File(fileName);
            final Scanner scanner = new Scanner(file);
            while (scanner.hasNextLine()) {
                // System.out.println(scanner.nextLine());
                inputLinesObject.add(scanner.nextLine());
            }
            scanner.close();
        } catch (final FileNotFoundException e) {
            e.printStackTrace();
        }
        return inputLinesObject;
    }
}

这有两个优点: - 您不修改 readFile 方法的输入参数 - 您不必处理 List 为空或 null 的情况