如何在构造函数java中自动生成数字

Question

我有两个构造函数：

private int num ;
private Room room ;
private boolean status;
private E_types type ;

1-：部分构造函数：

Instrument(int num)
Partial Constructor ~ use for initial key fields

2-：完整构造函数：

Instrument(Room room, boolean status, E_Types type)
Full Constructor ~ use for initial all fields instruments should be numbered automatically

这是什么自动编号？

谢谢:)

Answer 1

您需要类中的static 变量，该变量会随着每个 Instrument 的创建而自动增加。简单解释一下static 的含义：它是一个类的所有实例的变量。让它分配给num。

public class Instrument {
    private static int id = 0; // representing ID
    private int num = 0;
    private Room room ;
    private boolean status;
    private E_types type ;

    public Instrument(Room room, boolean status, E_Types type) {
        Instrument.id++;
        this.num = Instrument.id;
        this.room = room;
        this.status = status;
        this.type = type;
    }

    public static int getID() {
        return Instrument.id;
    }

    public int getNum() {
       return this.num;
    }
}

---

让我们用一个例子来试试。让我们在上面的构造函数的基础上创建 4 个 Instruments 并调用 getter 和返回最大 ID 的静态方法。

Instrument a = new Instrument(...);
Instrument b = new Instrument(...);
Instrument c = new Instrument(...);
Instrument d = new Instrument(...);

System.out.println(c.getNum()); // prints 3, num of "c" instrument
System.out.println(Instrument.getID()); // prints 4 (total of instruments)