为什么我的卡不打印到我的文本文件？

Question

I am writing a program to play poker.

Currently, I think the problem is in the shuffle method. It should generate 52 cards, all different from each other by generating a random number from 0 to 51 (52 in total), matching that "id" to a specific card (via a constructor in a class called "Card") and then checking to see if the card had already been generated. If it had, it wouldn't go through and the counter wouldn't count it. If it hadn't it would be printed in a text file called "Deck.txt", and so on untill the 52 cards had been printed.

The program seems to run fine but when I check the Deck.txt file, there's never anything there.

Here is my code:

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.NoSuchElementException;
import java.util.Random;
import java.util.Scanner;

public class Deck {

static private File deck = new File("Deck.txt");
static private Random shuffler = new Random();
static private Scanner dreader;

static public void shuffle() {
    int card;
    for (int i = 0; i < 52; i++) {
        card = shuffler.nextInt(52)+1;
        PrintWriter cwriter = null;
        try {
            cwriter = new PrintWriter(deck);
        } catch (FileNotFoundException e) {
            // File not found
        }
        if (DeckChecker(card)) {
            try {
                cwriter.println((new Card(card)).toString());
            } catch (NullPointerException e) {
                // File never opened
            }
        }
        else n--;
    }
}

private static boolean DeckChecker(int card) {
    try {
        dreader = new Scanner(deck);
    } catch (FileNotFoundException e) {
    }
    boolean switch1 = true;
    String s =  null;
    while (switch1) {
        try{
            s = dreader.nextLine();
        }catch(NoSuchElementException e){
            return true;
        }
        if (Card.getId(s) == card)
            return false;

    }
    return true;
}
}

.

public class Card {

static final private String[] number = { "2", "3", "4", "5", "6", "7", "8",
        "9", "10", "J", "Q", "K", "A" };
static final private String[] symbol = { "Diamond", "Spades", "Hearts",
        "Clubs" };
private String cnumber;
private String csymbol;
private String cardName;
private StringBuilder namer;

public Card(int id) {
    csymbol = symbol[(int) id / 13];
    cnumber = number[id - (((int) id / 13) * 13)];
    namer.append(cnumber).append(" of ").append(csymbol);
    cardName = namer.toString();
}

@Override
public String toString() {
    return cardName;
}

static public int getId(String card) {
    int s = 0;
    int n = 0;
    boolean switch1 = true;
    String cards = card.substring(6);
    String cardn = card.substring(0, 1);
    while (switch1) {
        if (cardn.equals(number[n]))
            switch1 = false;
        else
            n++;
    }
    switch1 = true;
    while (switch1) {
        if (cards.equals(number[s]))
            switch1 = false;
        else
            s++;
    }
    return (s * 13) + n;
}
}

Answer 1

First of all, this card doesn't compile. You have:

else n--;

Except n doesn't exist at that point.

You also create many different PrintWriter objects for that file, but never close the stream, meaning they're all in contention to write to the same file, which may be why it never writes to them.

All that being said, this is a really bad way to shuffle your deck of cards; it could try many, many times in a row looking for the last missing card, every time doing Disk IO which is one of the slowest things a program can do. Therefore, I've deleted the DeckChecker method entirely, as it's not needed.

Instead, just generate all the cards, then shuffle them, then write them to the file, like this:

import java.util.*; 

// snip, your code

public static void shuffleAndPrint() {
  List<Card> cardList = createShuffledDeck();
  writeDeckToFile(cardList);
}

private static List<Card> createShuffledDeck() {
  List<Card> cardList = new ArrayList<>();
  for (int i = 0; i < 52; i++) {
    cardList.add(new Card(i));
  }
  Collections.shuffle(cardList);
  return cardList;
}

private static void writeDeckToFile(List<Card> cardList) {
  try (PrintWriter cwriter = new PrintWriter(deck)) {
    for (Card c : cardList) {
      cwriter.println(c);
    }
  } catch (FileNotFoundException e) {
    e.printStackTrace();
  }
}