Java排序方法编译错误

Question

我遇到了这个错误:找不到符号 - 方法 sort(java.util.ArrayList)

我正在尝试对 ArrayList 进行排序并打印它。

这是代码，我还重写了 HockeyPlayer、Professor、Parent 和 GasStation 类中的 CompareTo 方法。谢谢。

import java.util.ArrayList;
import java.util.Iterator;
import java.util.Collections;
/**
 * Class Employees.
 */
public class Employees
{
    private ArrayList<Employee> employeeList;

    /**
     * Constructor for objects of class Employees
     */
    public Employees()
    {
        employeeList = new ArrayList<Employee>();
        //Creating 5 each types of Employees
        employeeList.add(new HockeyPlayer("Wayne Gretzky", 894));
        employeeList.add(new HockeyPlayer("Who Ever", 0));
        employeeList.add(new HockeyPlayer("Brent Gretzky", 1));
        employeeList.add(new HockeyPlayer("Pavel Bure", 437));
        employeeList.add(new HockeyPlayer("Jason Harrison", 0));

        employeeList.add(new Professor("Albert Einstein", "Physics"));
        employeeList.add(new Professor("Jason Harrison", "Computer Systems"));
        employeeList.add(new Professor("Richard Feynman", "Physics"));
        employeeList.add(new Professor("BCIT Instructor", "Computer Systems"));
        employeeList.add(new Professor("Kurt Godel", "Logic"));

        employeeList.add(new Parent("Tiger Woods", 1));
        employeeList.add(new Parent("Super Mom", 168));
        employeeList.add(new Parent("Lazy Larry", 20));
        employeeList.add(new Parent("Ex Hausted", 168));
        employeeList.add(new Parent("Super Dad", 167));

        employeeList.add(new GasStation("Joe Smith", 10));
        employeeList.add(new GasStation("Tony Baloney", 100));
        employeeList.add(new GasStation("Benjamin Franklin", 100));
        employeeList.add(new GasStation("Mary Fairy", 101));
        employeeList.add(new GasStation("Bee See", 1));
    }

    /**
     * Display the list of employee
     */
    public void displayEmployees()
    {
        Iterator <Employee> it = employeeList.iterator();
        while(it.hasNext()) {
            Employee e = it.next();
            System.out.println(e);

        }
    }
    /**
     * Display the list of employee sorted
     */
    public void displaySortedEmployees()
    {
        **Collections.sort(employeeList);**
        Iterator <Employee> it = employeeList.iterator();
        while(it.hasNext()) {
            Employee e = it.next();
            System.out.println(e);

        }
    }
}

我补充说:实现与 Employee 类相当，现在可以编译，但我需要比较不同的子类:HockeyPlayer、Parent 等等......调用该方法时，这是新的错误消息:java.lang.ClassCastException，教授无法转换为 HockeyPlayer

这是子类之一:

/**
 * Class HockeyPlayer.
 */
public class HockeyPlayer extends Employee implements Employable, Comparable<Employee>
{
    private       int     numberOfGoals;
    private       double  overTimePayRate ;

    /**
     * Constructor for objects of class Hockeyplayer
     */
    public HockeyPlayer(String name, int numberOfGoals)
    {
        super(name);
        overTimePayRate = 0.0;
        this.numberOfGoals = numberOfGoals;
    }

    /**
     * @return     overTimePayRate 
     */
    @Override
    public double getOverTimePayRate()
    {
        return overTimePayRate;
    }
    @Override
    public String   getDressCode()
    {
        return "jersey";
    }
    @Override
    public boolean  isPaidSalary()
    {
        return true;
    }
    @Override
    public boolean  postSecondaryEducationRequired()
    {
        return false;
    }
    @Override
    public String   getWorkVerb()
    {
        return "play";
    }
    @Override
    public boolean equals(Object that)
    {
        if(this == that){
            return true;
        }
        if(!(this instanceof HockeyPlayer)) {
            return false;
        }
        HockeyPlayer h = (HockeyPlayer) that;
        if(this.numberOfGoals == h.numberOfGoals) {
            return true;
        }
        return false;
    }
    @Override
    public int compareTo(Employee that)
    {
        if(this == that) {
            return 0;
        }

        HockeyPlayer h = (HockeyPlayer) that;

        if(this.numberOfGoals > h.numberOfGoals) {
            return +1;
        }
        else {
            return -1;
        }
    }
}

Answer 1

我猜测是你还没有声明 Employee实现Comparable<Employee> ，所以public static <T extends Comparable<? super T>> void sort(List<T> list)不适用...但很难说，因为您还没有提出Employee类。

这肯定是我在尝试您的代码时收到的错误消息:

class Employee {}

但是当我使用时它会编译:

class Employee implements Comparable<Employee> {

    // Obviously incorrect implementation, only used for demonstrating
    // that the code will now compile.
    public int compareTo(Employee other) {
        return 0;
    }
}

假设其他各种类是 Employee 的子类，您需要弄清楚如何比较(例如)HockeyPlayer和一个Parent 。不要忘记，任何员工都需要与任何其他员工进行比较。根据我的经验，继承和比较(无论是相等还是排序)很少能干净利落地工作......

如果您可以发布一个简短但完整的程序来演示该问题，那将非常有帮助。