为什么此类的每个对象对其成员都具有相同的值？

Question

I'm writting an application which should be extremely simple but it keeps using the last set values for name and boxesSold for everything. Here's a minimal example:

public class BandBoosterDriver
{
  public static void main (String[] args)
  {
    BandBooster booster1 = new BandBooster("First");
    BandBooster booster2 = new BandBooster("Second");
    booster2.updateSales(2);

    System.out.println(booster1.toString());
    System.out.println(booster2.toString());
  }
}

and here is the problem class:

public class BandBooster
{
  private static String name;
  private static int boxesSold;

  public BandBooster(String booster)
  {
    name = booster;
    boxesSold = 0;
  }

  public static String getName()
  {
    return name;
  }

  public static void updateSales(int numBoxesSold)
  {
    boxesSold = boxesSold + numBoxesSold;
  }

  public String toString()
  {
    return (name + ":" + " " + boxesSold + " boxes");
  }
}

This produces

Second: 2 boxes
Second: 2 boxes

But I would expect

First: 0 boxes
Second: 2 boxes

How can I get it to work the way I expect it to?

Answer 1

remove the static keyword. static will indicate your program to use single memory address for this field , and avoid allocating dedicated memory for this field everytime you create an instance of BandBooster.

Answer 2

因为它没有任何实例成员，所以只有静态成员。

Answer 3

Statically created variables are unique to the class and shared by all instances of it. What you are seeing is what's supposed to happen.