Java-为对象的每个实例赋予唯一编号 [英] Java- give every instance of object an unique number

问题描述

我在用Java编写一个简单的程序时遇到麻烦.

I'm having trobule writing a simple program in java.

我有一个叫票的班级，在那里:

I have a class called ticket, where I have:

public class Ticket {
public String movieTitle = null;
public static Integer movieNumber = 0;
public final Integer currentMovieNumber;

public Ticket(String movieTitle) {
    currentMovieNumber = movieNumber++;
    this.movieTitle = movieTitle;
}

}

现在，当我在另一个类中调用票证并运行程序以获取ID的编号时，它们都是一样的. 如果我叫出3张票，则每个id/movieNumber为3，当我叫出2张票时，id为2. 有人可以帮我吗?我以为使用static和final会有所帮助，但我想我缺少了一些东西.

Now when I call the ticket out in another class and run the program to get the numbers of the id's, they're all the same. If I call out 3 tickets, every id/movieNumber is 3, when I call out 2 tickets, the id will be 2. Can someone please help me with this ? I thought using static and final would help me but I guess there's is something I am missing.

推荐答案

听起来好像您正在从另一个类中查看movieNumber，这是不合适的.我会这样写:

It sounds like you're looking at movieNumber from your other class, which isn't appropriate. I would write it like this:

import java.util.concurrent.atomic.AtomicInteger;

public class Ticket {
    private static final AtomicInteger ticketCounter = new AtomicInteger();
    private final int ticketId;
    private final String movieTitle; // Or a reference to a Movie...

    public Ticket(String movieTitle) {
        this.movieTitle = movieTitle;
        this.ticketId = ticketCounter.incrementAndGet();
    }

    public int getTicketId() {
        return ticketId;
    }

    public String getMovieTitle() {
        return movieTitle;
    }
}

现在这些字段是私有的，其他类不能看到错误的值-相反，它们只能获取特定票证的ID和标题.他们没事看着柜台.

Now that the fields are private, other classes can't look at the wrong value - instead, they can only get at the ID for a particular ticket, and the title. They have no business looking at the counter.

其缺点是您不能轻易重置计数器或在下次运行程序时恢复计数器等.为此，您可能需要具有实例的TicketFactory 字段和createTicket的实例方法，该方法通过为其分配下一个ID等来创建票证.Ticket本身不知道计数器.

The downside of this is that you can't easily reset the counter, or resume it when you next run the program, etc. To achieve that, you might want a TicketFactory which has an instance field for the counter, and an instance method of createTicket which creates a ticket by assigning it the next ID etc. Ticket itself then wouldn't know about the counter.

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