如何从 input.txt 文件创建字符串数组

Question

我在创建从命令行读取为参数的数组时遇到问题。该文件的第一行是一个整数 N，该文件的其余部分在每一行都包含字符串。第一个整数是数组的大小。我已经成功分配了数组，但是我无法让它读取 input.txt 文件的整行。

以下是 input.txt 文件的示例：

4
hey, 03982
bye, 30980324
no, 3290823
yes, 30948432

这是我的代码截图：

import java.util.Scanner;
import java.io.*;
import java.util.Arrays;

class databaseSearch{

public static void main( String[] args ){

    Scanner sc = null;

    // if no arguments are entered, print out 
    // error message and correct way to invoke program
    if(args.length == 0){
            errorMessage();
    }

// Try and open the first argument on the command line
    try{
        sc = new Scanner(new File(args[0]));
    }catch(FileNotFoundException e){
        System.err.println(e.getMessage());
        errorMessage();
    }


int arraySize = sc.nextInt();
sc.nextLine();
String[] DB = new String[arraySize];
for( int i = 0; i < arraySize; i++ ){
    DB[i] = sc.nextLine();
}



    System.out.println(Arrays.toString(DB));

}

// errorMessage()
// prints out an error message with correct with to invoke program
// terminates after instructions are given
static void errorMessage(){
    System.err.println("Please try again by running the program along with a correct file.");
    System.exit(1);
}
}

Answer 1

使用Files.readAllLines().

List<String> lines = Files.readAllLines(Paths.get(arg[0]));
if (lines.isEmpty())
  throw new IllegalArgumentException("Empty file");
int count = Integer.parseInt(lines.remove(0)); 
if (lines.size() != count)
  throw new IllegalArgumentException("Incomplete file");
String[] db = lines.toArray(new String[count]);

Answer 2

由于您知道文件的结构，因此您的外部 while 循环看起来不必要且危险。取而代之的是获取您的扫描仪，从文件中获取第一个 int，使用该 int 创建您的数组，然后循环该数字次，就是这样。

伪代码

get scanner for file
read in first int, call it arraySize. Note that nextInt() does not get the end of line token
get nextLine from scanner **and discard it** to handle the end of line token
create a String array arraySize length.
for int i goes from 0 to less than arraySize
   get a line from the Scanner
   put line in your String array
   //  Split the line using String split. // not sure if this needs to be done
end for loop
close scanner

旁注：您需要学习和使用 Java 命名约定，包括以小写字母开头的变量和方法名称，以及以大写字母开头的类名称。遵循这些规则将允许您创建其他人（我们！）可以更轻松地遵循的代码。

例如，

public static void main(String[] args) {
    if (args.length == 0) {
        // !! exit/error
    }

    String filePath = args[0];
    String[] lines = null;

    // use try with resources so that the resource, here the Scanner
    // gets closed when done being used.
    try (Scanner scan = new Scanner(new File(filePath))) {
        int arraySize = scan.nextInt();  // get first int
        scan.nextLine();  // swallow the end-of-line token
        lines = new String[arraySize];
        for (int i = 0; i < lines.length; i++) {
            lines[i] = scan.nextLine();
        }

        System.out.println("Display results:");
        for (String line : lines) {
            System.out.println(line);
        }
    } catch (FileNotFoundException e1) {
        e1.printStackTrace();
    }
}

Answer 3

请参考以下 URL 以获取示例代码： http://javamanikandan.blogspot.com/2015/10/reading-file-into-collection-or-array.html