java - Java中如何计算一个对象的实例数？

Question

现在我正在开发一个基本的 java 程序，它将一些参数带入构造函数中以获取一杯咖啡。这很简单，但我在创建一种方法来对我创建的咖啡杯数量进行求和时遇到了困难。

到目前为止，这是我创建的 UseCoffee 类:

public class UsesCoffee{ 
   public static void main(String args[]) {
     System.out.println("cups created: " + Coffee.totalCups());

    Coffee cup1 = new Coffee(350, "mint", true);
    System.out.println("cup1: " + cup1);
    Coffee cup2 = new Coffee(500, "mocha", false);
    System.out.println("cups created: " + Coffee.totalCups());
    System.out.println("cup2: " + cup2);
    Coffee cup3 = new Coffee(350, "no flavour used", false);
    cup3.doubleSize();
    System.out.println("cup3: " + cup3);

    Coffee cup4 = new Coffee(-10, "mocha", false);
    System.out.println("cup4: " + cup4);

    System.out.println("cups created: " + Coffee.totalCups());

    if (Coffee.bigger(cup3,cup2))
    System.out.println("cup3 is bigger than cup2");

    if (Coffee.bigger(cup1,cup2))
    System.out.println("cup1 is bigger than cup3");

  if (Coffee.bigger(cup1,cup1))
  System.out.println("cup1 is bigger than itself");
 } // end main
} // end UsesCoffee

这是我创建的咖啡类:

public class Coffee {
    private int coffeeVol;
    private String coffeeFlav;
    private boolean yesCream;

    public Coffee(int volume, String flavour, boolean cream) {
        this.coffeeFlav = flavour;
        this.coffeeVol = volume;
        this.yesCream = cream;
        if (volume < 0) {
            System.out.println("error: negative size. Defaultsize of 250 ml used");
            coffeeVol = 250;
        }

    }

    public String toString() {
        return coffeeVol +"ml, " + coffeeFlav + ", " + yesCream;
     } // end toString

---

    public static int totalCups() {
         //THIS IS WHERE I'M HAVING TROUBLE
    }

---

    public int doubleSize() {
        coffeeVol = coffeeVol*2;
        return coffeeVol;
    }


}

有没有办法计算咖啡杯的数量？我在这方面确实迷失了方向，非常感谢任何帮助!

Answer 1

您可以向 Coffee 类添加一个静态变量，并在构造函数中递增它。

类似的事情:

public class Coffee {
    private static int numberOfCups = 0;
    private int coffeeVol;
    private String coffeeFlav;
    private boolean yesCream;

    public Coffee(int volume, String flavour, boolean cream) {
        this.coffeeFlav = flavour;
        this.coffeeVol = volume;
        this.yesCream = cream;
        if (volume < 0) {
            System.out.println("error: negative size. Defaultsize of 250 ml used");
            coffeeVol = 250;
        }
        numberOfCups++;
    }

    public String toString() {
        return coffeeVol +"ml, " + coffeeFlav + ", " + yesCream;
    } // end toString

    public static int totalCups() {
         return numberOfCups;
    }

    public int doubleSize() {
        coffeeVol = coffeeVol*2;
        return coffeeVol;
    }

    public static boolean bigger(Coffee cup1, Coffee cup2) {
        if (cup1.coffeeVol > cup2.coffeeVol) {

            return true;
        }
        return false;
    }
}