我有一个主类，我定义了一个Seat类型的二维数组，然后使用一个方法随机选择一个座位元素并将其设置为“预订”
但是，如果必须随机选择多于1个（有时即使只需要随机选择一个）座位元素，也会返回此错误：
"Exception in thread "main" java.lang.NullPointerException
at cinemasystem.Seat.bookSeat(Seat.java:173)
at cinemasystem.CinemaSystem.main(CinemaSystem.java:70)
Java Result: 1"
我不知道我做错了什么，可能是我的随机生成方法，无论如何任何帮助都会受到赞赏。
主要课程：
public static void main(String[] args) {
Seat cinemaactual = new Seat("Cinema");
Seat[][] cinema = new Seat[12][23];
Seat bookedSeat = new Seat("");
Ticket ticket = new Ticket();
Scanner scan = new Scanner(System.in);
String answer, contiune, list;
cinemaactual.CreateTheatre(cinema);
int number, check = 0, category, id;
do {
System.out.print("Welcome to the Theatre Booking System. (QUIT to exit)"
+ "\nWould you like to purchase tickets or list available seats?"
+ "(/Purchase/List/Help)");
answer = scan.nextLine();
if (answer.equalsIgnoreCase("purchase")) {
do {
System.out.println("Please choose the cateogry of ticket "
+ "you would like, followed by who the ticket is for"
+ "and the amount required. (separated by a space)\n"
+ "1. Gold\n2. Silver\n3. Bronze\n\n1. Adult\n2."
+ " Child\n3. Concession");
category = scan.nextInt();
check = category;
id = scan.nextInt();
number = scan.nextInt();
if (category == 1 || category == 2 || category == 3 && id == 1 || id == 2 || id == 3) {
ticket.SetType(category);
if (category == 1) {
ticket.SetName("Gold");
} else if (category == 2) {
ticket.SetName("Siler");
} else {
ticket.SetName("Bronze");
}
ticket.SetNumber(number);
ticket.SetID(id);
if (id == 1) {
ticket.SetCategory("Adult");
} else if (id == 2) {
ticket.SetCategory("Child");
} else {
ticket.SetCategory("Bronze");
}
System.out.print("You have selected "
+ ticket.GetNumber() + " " + ticket.GetName()
+ " ticket(s) at the " + ticket.GetCategory() + " price.");
System.out.println();
ticket.BuyTicket(category, id);
bookedSeat = Seat.bookSeat(cinema, number);
} else {
System.out.print("Sorry, incorrect input, please enter an apropriate value.");
check = scan.nextInt();
}
} while (check == 0 || check > 3);
do {
System.out.print("Would you like to perchase more tickets? (Yes/No)");
contiune = scan.nextLine();
if (contiune.equalsIgnoreCase("Yes")) {
System.out.print("Would you like to list available seats? (Yes/No) (A/G/S/B)");
list = scan.nextLine();
cinemaactual.DisplayTheatre(cinema);
if (list.equalsIgnoreCase("Yes")) {
cinemaactual.DisplayTheatre(cinema);
}
}
在座位类中随机选择座位的方法：
public static Seat bookSeat(Seat[][] x, int number){
int count = 0;
Seat book = new Seat("");
Random rand = new Random();
while(count < number){
if (x != null) {
do {
book = x[rand.nextInt(x.length)][rand.nextInt(x.length)];
book.bookSeat(true);}
while (book.isBooked());
} count++; }
return book;
}
Seat Class的第172和173行
172：book = x[rand.nextInt(x.length)][rand.nextInt(x.length)];
173：book.bookSeat(true);}
在座位类中的CreateTheatre方法：
public Seat[][] CreateTheatre(Seat[][] x) {
for (int row = 0; row < 8; row++) {
for (int col = 0; col < 4; col++) {
x[row][col] = new Seat("B");
}
}
for (int row = 8; row < 12; row++) {
for (int col = 0; col < 4; col++) {
x[row][col] = new Seat("S");
}
}
for (int row = 0; row < 8; row++) {
for (int col = 19; col < 23; col++) {
x[row][col] = new Seat("B");
}
}
for (int row = 8; row < 12; row++) {
for (int col = 19; col < 23; col++) {
x[row][col] = new Seat("S");
}
}
for (int row = 3; row < 5; row++) {
for (int col = 4; col < 9; col++) {
x[row][col] = new Seat("B");
}
}
for (int row = 3; row < 5; row++) {
for (int col = 14; col < 19; col++) {
x[row][col] = new Seat("S");
}
}
for (int row = 9; row < 12; row++) {
for (int col = 7; col < 4; col++) {
x[row][col] = new Seat("S");
}
}
for (int row = 3; row < 5; row++) {
for (int col = 14; col < 20; col++) {
x[row][col] = new Seat("B");
}
}
for (int row = 5; row < 9; row++) {
for (int col = 4; col < 9; col++) {
x[row][col] = new Seat("S");
}
}
for (int row = 5; row < 9; row++) {
for (int col = 14; col < 20; col++) {
x[row][col] = new Seat("S");
}
}
for (int row = 6; row < 9; row++) {
for (int col = 9; col < 14; col++) {
x[row][col] = new Seat("G");
}
}
for (int row = 9; row < 12; row++) {
for (int col = 7; col < 16; col++) {
x[row][col] = new Seat("G");
}
}
for (int row = 9; row < 12; row++){
for (int col = 4; col < 7; col++){
x[row][col] = new Seat("S");
}
}
for (int row = 9; row < 12; row++){
for (int col = 16; col < 19; col++){
x[row][col] = new Seat("S");
}
}
return x;
}
答案 0 :(得分：1)
如果您检查了CreateTheatre逻辑，则cinema内的值可能为空。通过一个循环将默认值放在数组中。
以行0为例，您只需将值从0填充到4，然后填充19到23。除此之外，我没有看到你填补价值。
for(int i = 0; i<cinema.length;i++)
for(int j=0; j<cinema[i].length;j++)
cinema[i][j] = new Seat("");
更新：
如果不想放空座位，那么您可以在调用book.bookSeat(true)
if(book != null){
book.bookSeat(true);
}
您可以使用Arrays.deepToString(cinema)打印多维数组。
正如其他主题中所指出的那样book = x[rand.nextInt(12)][rand.nextInt(23)]
答案 1 :(得分：1)
我不确定这是否是你收到错误的原因，我不知道会发生什么行，但现在这是错的：
你这样做：
Seat[][] cinema = new Seat[12][23];
然后你这样做：
book = x[rand.nextInt(x.length)][rand.nextInt(x.length)];
相当于：
book = x[rand.nextInt(12)][rand.nextInt(12)]
当我假设你真正想做的事情是：
book = x[rand.nextInt(12)][rand.nextInt(23)]
考虑一下：
Seat[] y = x[rand.nextInt(x.length)];
book = y[rand.nextInt(y.length)];
答案 2 :(得分：1)
我认为NullPointerException异常的根本原因在于CreateTheatre方法。请确保座椅阵列的所有行和列（即12 * 23）都填充了Seat对象。
一些观察结果：
由于col已使用7进行初始化并与<4进行比较，因此此循环似乎无效。
for (int row = 9; row < 12; row++) {
for (int col = 7; col < 4; col++) {
x[row][col] = new Seat("S");
}
}
此循环
for (int row = 3; row < 5; row++) {
for (int col = 14; col < 19; col++) {
x[row][col] = new Seat("S");
}
}
似乎与此循环重叠，因为它使用相同的行但重叠的列。
for (int row = 3; row < 5; row++) {
for (int col = 14; col < 20; col++) {
x[row][col] = new Seat("B");
}
}
最后，几个席位未初始化，如下所示，在NullPointerException方法中使用时会导致bookSeat()。
B, B, B, B, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, B, B, B, B
B, B, B, B, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, B, B, B, B
B, B, B, B, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, B, B, B, B
B, B, B, B, B, B, B, B, B, null, null, null, null, null, B, B, B, B, B, B, B, B, B
B, B, B, B, B, B, B, B, B, null, null, null, null, null, B, B, B, B, B, B, B, B, B
B, B, B, B, S, S, S, S, S, null, null, null, null, null, S, S, S, S, S, S, B, B, B
B, B, B, B, S, S, S, S, S, G, G, G, G, G, S, S, S, S, S, S, B, B, B
B, B, B, B, S, S, S, S, S, G, G, G, G, G, S, S, S, S, S, S, B, B, B
S, S, S, S, S, S, S, S, S, G, G, G, G, G, S, S, S, S, S, S, S, S, S
S, S, S, S, S, S, S, S, S, G, G, G, G, G, S, S, S, S, S, S, S, S, S
S, S, S, S, S, S, S, S, S, G, G, G, G, G, S, S, S, S, S, S, S, S, S
S, S, S, S, S, S, S, S, S, G, G, G, G, G, S, S, S, S, S, S, S, S, S
如果您想初始化所有席位，我认为您可能希望更新CreateTheatre中的循环，如下所示：
for (int row = 0; row < 8; row++) {
for (int col = 0; col < 4; col++) {
x[row][col] = new Seat("B");;
}
}
for (int row = 8; row < 12; row++) {
for (int col = 0; col < 4; col++) {
x[row][col] = new Seat("S");;
}
}
for (int row = 0; row < 8; row++) {
for (int col = 19; col < 23; col++) {
x[row][col] = new Seat("B");;
}
}
for (int row = 0; row < 3; row++) {
for (int col = 4; col < 20; col++) {
x[row][col] = new Seat("G");;
}
}
for (int row = 8; row < 12; row++) {
for (int col = 19; col < 23; col++) {
x[row][col] = new Seat("S");;
}
}
for (int row = 3; row < 5; row++) {
for (int col = 4; col < 9; col++) {
x[row][col] = new Seat("B");;
}
}
for (int row = 3; row < 5; row++) {
for (int col = 8; col < 20; col++) {
x[row][col] = new Seat("S");;
}
}
for (int row = 9; row < 12; row++) {
for (int col = 7; col < 14; col++) {
x[row][col] = new Seat("S");;
}
}
for (int row = 9; row < 12; row++) {
for (int col = 14; col < 20; col++) {
x[row][col] = new Seat("B");;
}
}
for (int row = 5; row < 9; row++) {
for (int col = 4; col < 9; col++) {
x[row][col] = new Seat("S");;
}
}
for (int row = 5; row < 9; row++) {
for (int col = 14; col < 20; col++) {
x[row][col] = new Seat("S");;
}
}
for (int row = 5; row < 9; row++) {
for (int col = 9; col < 14; col++) {
x[row][col] = new Seat("G");;
}
}
for (int row = 9; row < 12; row++) {
for (int col = 7; col < 16; col++) {
x[row][col] = new Seat("G");;
}
}
for (int row = 9; row < 12; row++){
for (int col = 4; col < 7; col++){
x[row][col] = new Seat("S");;
}
}
for (int row = 9; row < 12; row++){
for (int col = 16; col < 19; col++){
x[row][col] = new Seat("S");;
}
}
此外，，因为您的行和列不相同（座位[12] [23] - > 12行和23列），我想您要在{更改此声明{1}}方法：
bookSeat()使用 book = x[rand.nextInt(x.length)][rand.nextInt(x.length)];
作为列标题，如下所示：
x[0].length