java如何创建一个将数组添加到arraylist并对其调用方法的主方法？

Question

我有一个类，它的目的是从ArrayList中的数组中获取类型为double的值，并按定义的速率增加它们：

import java.util.ArrayList;

public class Company {
    static ArrayList<Employee> employees;

    public Company() {
        Company.employees = new ArrayList<Employee>();
    }


    public static ArrayList<Employee> getEmployees() {
        return employees;
    }

    public static void setEmployees(ArrayList<Employee> employees) {
        Company.employees = employees;
    }

    public void increaseSalaries(double rate) {
        if (rate <= 0.0) {
            throw new IllegalArgumentException();
        } else {
            for (int i = 0 ; i < employees.size() ; i++) {
                employees.get(i).increaseSalaries(rate);
            }
        }
    }
}

我想写一个main方法来构建一个arraylist并在其上调用该方法，但我不确定如何实现。到目前为止我有

public static void main(String[] args) {
    Company businesstown;
    HourlyEmployee george;
    MonthlyEmployee ambrose;
    george = new HourlyEmployee("George", "McClellan", "1537", 1.04);
    ambrose = new MonthlyEmployee("Ambrose", "Burnside", "1536", 741.0);
}

但是我不确定如何将这些数组添加到ArrayListbusinesstown。我已经尝试了很多.add(george);的组合，但我做不好。要么它说

the method add(HourlyEmployee) is not defined for type Company

或者它编译并抛出一个NullPointerException

（我应该补充HourlyEmployee和MonthlyEmployee都是扩展Employee的类）

Answer 1

在我看来，最好将ArrayList设置为类的私有成员，并使用add方法添加员工

public class Company {
    private ArrayList<Employee> employees;

    public Company() {
        employees = new ArrayList<Employee>();
    }

    public void addEmployee(Employee e) {
        employees.add(e);
    }
    //rest of code
}

大体上

public static void main(String[] args) {
    Company businesstown = new Company();
    HourlyEmployee george = new HourlyEmployee("George", "McClellan", "1537", 1.04);
    MonthlyEmployee ambrose = new MonthlyEmployee("Ambrose", "Burnside", "1536", 741.0);
    businesstown.add(george);
    businesstown.add(ambrose);
}

Answer 2

您可以将它们添加到getEmployees返回的List：

businesstown.getEmployees().add(george);
businesstown.getEmployees().add(ambrose);

但是在访问businesstown之前，请确保初始化实例及其内的employees

Company businesstown = new Company(); // since for you this is initialisin the list as well