如何在java中查找数组中某个特定对象的类型

I have 4 classes. 1) Employee class 2) Nurse class that extends Employee 3) Doctor class that also extends Employee 4) Supervisor class that extends Doctor

我有4节课。 1)员工类2)扩展员工的护士班3)也扩展员工的博士班4)扩展博士的监督班

Inside Supervisor I have a property: private Employee[] arrayOfEmployees;

在Supervisor中我有一个属性:private Employee [] arrayOfEmployees;

Basically an array of Employees that inside are doctors and nurses. now i want to build a function inside the Supervisor class that will return the number of nurses within the array.

基本上是一系列员工,里面是医生和护士。现在我想在Supervisor类中构建一个函数,它将返回数组中的护士数量。

My problem is that I don't know how to access the array because the array type is Employee and I look for Nurse.

我的问题是我不知道如何访问数组,因为数组类型是Employee,我寻找Nurse。

Can someone help me with this function?

有人可以帮我这个功能吗?

4 个解决方案

#1

If you use java 8 you can use streams for this:

如果您使用java 8,则可以使用以下流:

int numNurses = Arrays
    .stream(employeeArray)
    .filter(e -> e instanceof Nurse.class)
    .count();

#2

Just with the instanceof keyword.

只需使用instanceof关键字。

if (arrayOfEmployees[i] instanceof Nurse) {
    Nurse nurse = (Nurse) arrayOfEmployees[i];
}

#3

Using java 8 and streams

使用java 8和流

//array of employees 3 Nurses & 2 Docs
E[] aOfE = new E[] { new N(), new N(), new N(), new D(), new D() };

Predicate<E> pred = someEmp -> N.class.isInstance(someEmp);
System.out.println(Arrays.stream(aOfE).filter(pred).count());

where the class:

班级:

E=Employee, N=Nurse, D=Doctor

or using lambdas

或者使用lambdas

E[] aOfE = new E[] { new N(), new N(), new N(), new D(), new D() };


System.out.println(Arrays.stream(aOfE).filter(someEmp -> N.class.isInstance(someEmp)).count());

#4

public class Main {

    public static void main(String[] args) {
        Supervisor supervisor = new Supervisor();
        supervisor.arrayOfEmployees = new Employee[] {new Nurse(), new Doctor(), new Doctor(), new Nurse()};

        //will be 2
        long numberOfNurses = supervisor.numberOfNurses();

        System.out.println(numberOfNurses);
    }
}

class Employee {}

class Doctor extends Employee {}

class Nurse extends Employee {}

class Supervisor extends Doctor {
    Employee[] arrayOfEmployees;

    long numberOfNurses() {
        return Stream.of(arrayOfEmployees).filter(e -> e instanceof Nurse).count();
    }
}

#1