无法让扫描仪从文件中读取

Question

I am making a Battle Royale game in command line, and I have the bots' First Names and Last Names in two text files. Now I'm trying to read from these two files with 2 Scanners, then put the First names in one array, and the Last names in another array.

The game is in Object Oriented so there's 3 files:

File #1 (App)

package tp2;

public class App {

    public static void main(String[] args) throws InterruptedException {
        Game game = new Game();
        game.start();
    }    
}

File #2 (Game)

package tp2;

public class Game {

    private Level currentLevel;
    private Player player;

    public void start() throws InterruptedException {
        World.createNameArrays();
        World.printNamesArrays();              
    }
}

File #3 (World)

package tp2;

import java.io.*;
import java.util.*;
import java.util.concurrent.TimeUnit;

public class World {
    private static final int MAX_PLAYERS = 42;
    private static String firstNamesArray[] = new String[MAX_PLAYERS];
    private static String lastNamesArray[] = new String[MAX_PLAYERS];
    private static Player players[] = new Player[MAX_PLAYERS];

    private static Scanner scannerFirstNames;
    private static Scanner scannerLastNames;

    public static void printNamesArrays() {
        System.out.println("");
        System.out.println("First names available");
        System.out.println("---------------------");
        for (int i = 0; i < MAX_PLAYERS; ++i) {
            System.out.println(firstNamesArray[i]);
        }
        System.out.println("");
        System.out.println("Lats names available");
        System.out.println("---------------------");
        for (int i = 0; i < MAX_PLAYERS; ++i) {
            System.out.println(lastNamesArray[i]);
        }
    } 

    public static void createNameArrays() {        
        openNameFiles();
        int i = 0;
        while (scannerFirstNames.hasNext() && scannerLastNames.hasNext()) {
            System.out.println("**********Test*************");
            firstNamesArray[i] = scannerFirstNames.nextLine();
            lastNamesArray[i] = scannerLastNames.nextLine();
            ++i;            
        }
        closeNameFiles();
    }

    public static void closeNameFiles() {
        scannerFirstNames.close();        
        scannerLastNames.close();
    }

    public static void openNameFiles() {
        try {
            scannerFirstNames = new Scanner(new File("firstnames.txt"));
        } catch(FileNotFoundException e) {
            System.out.println("Error! File not found.");
        }
        try {
            scannerLastNames = new Scanner(new File("lastnames.txt"));
        } catch(FileNotFoundException e) {
            System.out.println("Error! File not found.");
        }        
    }
}

For clarification, I made a method to print the First names and Last names from the two arrays, but it just prints "NULL" when I execute the method. That would just mean that the Scanners can't read the two files for some reasons...

Answer 1

You can modify the createNamesArray() function and get rid of closeNameFiles() and openNameFile()

I've updated your World.java (in case you are using java:8)

public class World {

  private static final int MAX_PLAYERS = 42;
  private static String firstNamesArray[] = new String[MAX_PLAYERS];
  private static String lastNamesArray[] = new String[MAX_PLAYERS];
  private static int firstNameEntriesInFile;
  private static int lastNameEntriesInFile;

  public static void printNamesArrays() {
    System.out.println("");
    System.out.println("First names available");
    System.out.println("---------------------");
    for (int i = 0; i < MAX_PLAYERS && i < firstNameEntriesInFile; ++i) {
      System.out.println(firstNamesArray[i]);
    }
    System.out.println("");
    System.out.println("Lats names available");
    System.out.println("---------------------");
    for (int i = 0; i < MAX_PLAYERS && i < lastNameEntriesInFile; ++i) {
      System.out.println(lastNamesArray[i]);
    }
  }

  public static void createNameArrays() {
    try {
      String[] fNames = Files.lines(new File("fullpath/firstname.txt").toPath()).toArray(String[]::new);
      if (fNames.length == 0) {
        throw new RuntimeErrorException(null, "no first name entry found in the given file");
      } else {
       firstNameEntriesInFile=fNames.length;
       firstNamesArray=fNames;
      }
      String[] lNames = Files.lines(new File("fullpath/lastname.txt").toPath()).toArray(String[]::new);
      if (lastNamesArray.length == 0) {
        throw new RuntimeErrorException(null, "no last name entry found in the given file");
      }else {
        lastNameEntriesInFile=lNames.length;
        lastNamesArray=lNames;
       }
    } catch (IOException e) {
      e.printStackTrace();
      System.out.println("file can't be accessed: cause " + e.getMessage());
    }
  }
}

Still, if you would like to do it your way my suggestion will be to use FileReader

I would recommend using an ArrayList, which handles dynamic sizing, whereas an array will require a defined size up front, which you may or may not know. Looking at your code I see you have already defined the size.

BufferedReader in = new BufferedReader(new FileReader("fullpath/firstnames.txt"));
String str;

List<String> list = new ArrayList<String>();
while((str = in.readLine()) != null){
    list.add(str);
}

firstNamesArray = list.toArray(new String[list.size()]);

similarly for last name array.

Also, it's not wise to use static first and foremost reason being thread safety second Obj-Oriented concepts.

Don't worry we all were in your shoes one day, then we learned with time. Not a big deal!