java - 如何对扩展类的 ArrayList 进行排序？

Question

这是一个主类 Employee.java和另外 2 个扩展主类的类。 ArrayList<Employee>包含来自 createFixedEmployee.java 的对象和 createPerHourEmployee .如何对 ArrayList 中的对象进行排序按薪水排序，如果某些对象的薪水相同，则按字母顺序对它们的名字进行排序？

我尝试使用 Comparator.comparing();但不起作用，我收到错误 Cannot resolve method getMonthSalary();这是一个代码:

createPerHourEmployee.java

public class createPerHourEmployee extends Employee {
    private double salary;

    public createPerHourEmployee() {}

    public double getSalaryPerHour() { return this.salary; }

    public double setSalaryPerHour(double value) {
        return this.salary = value;
    }


    public createPerHourEmployee (int _id, String _name, double _salary) {
        setEmployeeID(_id);
        setEmployeeName(_name);
        this.salary = _salary;
    }

    public double getMonthSalary() {
        return salary * (20 * 0.8);
    }

    public String toString() {
        return getEmployeeID() + ", " + getEmployeeName() + ", " + getSalaryPerHour();
    }
}

createFixedEmployee.java

public class createFixedEmployee extends Employee {
    private double salary;

    public createFixedEmployee() {}

    public double getSalaryFixed() {
        return this.salary;
    }

    public double setSalaryFixed(double value) {
        return this.salary = value;
    }

    public createFixedEmployee(int _id, String _name, double _salary) {
        setEmployeeID(_id);
        setEmployeeName(_name);
        this.salary = _salary;
    }

    public double getMonthSalary() {
        return this.salary;
    }

    public String toString() {
        return getEmployeeID() + ", " + getEmployeeName() + ", " + getSalaryFixed();
    }

}

员工.java

import java.util.ArrayList;
import java.util.Comparator;

public abstract class Employee {
    private int base_id;
    private String base_name;

    public int getEmployeeID () {
        return this.base_id;
    }

    public int setEmployeeID (int value) {
        return this.base_id = value;
    }

    public String getEmployeeName () {
        return this.base_name;
    }

    public String setEmployeeName(String value) {
        return this.base_name = value;
    }

    public abstract double getMonthSalary();

    public static void main(String[] argc) {
        ArrayList<Employee> Employee = new ArrayList<Employee>();
        Employee.add(new createPerHourEmployee(1, "asd", 1300));
        Employee.add(new createFixedEmployee(7, "asds", 14025));
        Employee.add(new createPerHourEmployee(2, "nikan", 1230));
        Employee.add(new createPerHourEmployee(3, "nikalo", 12330));
        Employee.add(new createFixedEmployee(6, "aaaa", 14025));
        Employee.add(new createFixedEmployee(4, "nikaq", 140210));
        Employee.add(new createFixedEmployee(5, "nikas", 124000));
        Employee.add(new createFixedEmployee(6, "nikab", 14025));


        Employee.sort(Comparator.comparing(Employee::getMonthSalary)
              .thenComparing(Employee::getEmployeeName)); // here is an error

    }
}

所以我尝试使用

Employee.sort(Comparator.comparing(createFixedEmployee::getMonthSalary).
                thenComparing(createFixedEmployee::getEmployeeName));

它工作正常，但我需要对所有类进行排序，而不仅仅是一个类。

Answer 1

排序 List<T> 时，您绝对可以使用对任何 T 的功能引用祖传之法。这里的问题是您给列表的名称 - 您已将局部变量命名为 Employee , 它隐藏了类型的名称 Employee当您尝试在 Comparator 中创建函数引用时.给它一个更好的名字，你应该没问题。例如:

ArrayList<Employee> employeeList = new ArrayList<Employee>();
// Or better yet: List<Employee> employeeList = new ArrayList<>();

employeeList.add(new createPerHourEmployee(1, "asd", 1300));
employeeList.add(new createFixedEmployee(7, "asds", 14025));
employeeList.add(new createPerHourEmployee(2, "nikan", 1230));
employeeList.add(new createPerHourEmployee(3, "nikalo", 12330));
employeeList.add(new createFixedEmployee(6, "aaaa", 14025));
employeeList.add(new createFixedEmployee(4, "nikaq", 140210));
employeeList.add(new createFixedEmployee(5, "nikas", 124000));
Employee.add(new createFixedEmployee(6, "nikab", 14025));


employeeList.sort(Comparator.comparing(Employee::getMonthSalary)
      .thenComparing(Employee::getEmployeeName));