java - 为什么在打印大型 ArrayLists 时会出现奇怪的字符

Question

我正在学习部分涉及打印 ArrayLists 元素的教程。该程序在处理小列表时完全按照我的预期运行。但是，当输入较大的数字时，字符串格式(我相信)会导致一些奇怪的结果。

我的代码如下:

public class Theatre {
    private final String theatreName;
    public List<Seat> seats = new ArrayList<>();

    public Theatre(String theatreName, int numRows, int seatsPerRow) {
        this.theatreName = theatreName;

        int lastRow = 'A' + (numRows -1);
        for (char row = 'A'; row <= lastRow; row++) {
            for(int seatNum = 1; seatNum <= seatsPerRow; seatNum++) {
                Seat seat = new Seat(row + String.format("%02d", seatNum));
                seats.add(seat);
            }
        }
    }

    public String getTheatreName() {
        return theatreName;
    }

    public boolean reserveSeat(String seatNumber) {
        int low = 0;
        int high = seats.size()-1;

        while(low <= high) {
            System.out.print(".");
            int mid = (low + high) /2;
            Seat midVal = seats.get(mid);
            int cmp = midVal.getSeatNumber().compareTo(seatNumber);

            if(cmp <0) {
                low = mid + 1;
            } else if(cmp > 0) {
                high = mid -1;
            } else {
                return seats.get(mid).reserve();
            }
        }

            System.out.println("There is no seat " + seatNumber);
            return false;


    }

    // for testing
    public void getSeats() {
        for(Seat seat : seats) {
            System.out.println(seat.getSeatNumber());
        }
    }

    public class Seat implements Comparable<Seat > {
        private final String seatNumber;
        private boolean reserved = false;

        public Seat(String seatNumber) {
            this.seatNumber = seatNumber;
        }

        public boolean reserve() {
            if(!this.reserved) {
                this.reserved = true;
                System.out.println("Seat " + seatNumber + " reserved");
                return true;
            } else {
                return false;
            }
        }

        public boolean cancel() {
            if(this.reserved) {
                this.reserved = false;
                System.out.println("Reservation of seat " + seatNumber + " cancelled");
                return true;
            } else {
                return false;
            }
        }

        public String getSeatNumber() {
            return seatNumber;
        }

        @Override
        public int compareTo(Seat seat) {
            // returns integer greater than 0 if greater than, less than if less than, 0 if equal
            return this.seatNumber.compareTo(seat.getSeatNumber());
        }
    }

使用 Main 方法类:

public static void main(String[] args) {
        Theatre theatre = new Theatre("Olympian", 800, 12);
        List<Theatre.Seat> seatCopy = new ArrayList<>(theatre.seats); // shallow copy, contains references to all
                                                                        // elements of both lists, original and copy
        printList(seatCopy);


        seatCopy.get(1).reserve();
        if (theatre.reserveSeat("A02")) {
            System.out.println("Please pay for A02");
        } else {
            System.out.println("seat already reserved");
        }

        // see that they are clearly two separate array lists
        Collections.reverse(seatCopy);
        System.out.println("Printing seat copy");
        printList(seatCopy);
        System.out.println("Printing theatre.seats");
        printList(theatre.seats);
        System.out.println("Shuffling seatCopy");
        Collections.shuffle(seatCopy);
        printList(seatCopy);

    }

    public static void printList(List<Theatre.Seat> list) {
        for (Theatre.Seat seat : list) {
            System.out.print(" " + seat.getSeatNumber());
        }
        System.out.println();
        System.out.println("===============================");
    }

}

输出(我只引用够看)是:

12 ͠11 ͠10 ͠09 ͠08 ͠07 ͠06 ͠05 ͠04 ͠03 ͠02 ͠01 ͟12 ͟
===============================
Printing theatre.seats
A01 A02 A03 A04 A05 A06 A07 A08 A09 A10
===============================
===============================
 Shuffling seatCopy
V07 Ý11 11 ű05 Ú02 ̄06 ̓01 ŕ12 ȣ03 Ǔ05 S07 

我知道我用完了字母字符并且此行中的格式为:

Seat seat = new Seat(row + String.format("%02d", seatNum));

仅用于处理格式为“X##”的席位。

我想了解的是奇怪字符出现的具体原因(“~”和“'”等)。显然，格式不合适。但为什么它会专门产生这种输出？

谢谢你的帮助，马克

Answer 1

你自己说的。您的字母字符用完了。事实上，您完全用完了 ASCII 字符。从这一行:

for (char row = 'A'; row <= lastRow; row++)

您正在做的是从“A”开始行字母并继续跨越 Unicode 字符集。因此，如果超过 26 行，您将开始得到像 ~ 这样的符号，而如果行数足够多，您将完全不使用 ASCII 并开始得到奇怪的行字母，例如 Ý。

如果您不希望这种情况发生，则需要放弃 for 循环并提出一种完全不同(且更复杂)的分配行标签的方法。