使用sort方法对Java编译错误进行排序
我遇到了这个错误: 找不到符号-方法排序(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P
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);
}
}
}
我添加了:实现可与Employee类进行比较,它现在可以编译了,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除此之外,教授不能被选为冰球运动员
以下是其中一个子类:
/**
* 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;
}
}
}
# 1 楼答案
我猜ypu已经声明Employee实现了comparable,因为您使用了@Override注释。另外,如果你没有这样做,你会得到一个编译时错误,而不是运行时错误。不过我有点困惑,因为你的问题标题说编译错误,但正文说你得到了一个例外。即使employee类实现了comparable,如果子类重写了compareTo()的实现,如果不小心,也可能会出现问题。当sort方法使用非hockeyPlayer参数调用您的hockeyPlayer的compareTo()方法时,您会遇到cast异常。我怀疑如果你删除@Override注释并将签名改为“public int compareTo(HockeyPlayer that)”,那么它会起作用,因为它在与非HockeyPlayer员工进行比较时会使用继承的compareTo(),而在与HockeyPlayer进行比较时会使用另一个。即使曲棍球运动员是雇员,如果有多个重载方法适用,Java也会使用最具体的重载方法。简而言之,我认为你想在这里超载,而不是超负荷
还有,不是你问的,但我认为值得问:
你真的想在这里用==吗
# 2 楼答案
我猜你还没有声明
Employee
实现Comparable<Employee>
,所以public static <T extends Comparable<? super T>> void sort(List<T> list)
不适用。。。但这很难说,因为你还没有向你的Employee
同学摆姿势这肯定是我在尝试您的代码时收到的错误消息:
但当我使用时,它会编译:
假设其他各种类都是
Employee
的子类,那么您需要计算出如何比较HockeyPlayer
和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(无论是为了平等还是排序)很少干净地工作如果你能发布一个简短但完整的程序来演示这个问题,那将非常有帮助
# 3 楼答案
Employee类应该实现接口
Comparable<Employee>
,而不仅仅是让它的所有子类实现方法compareTo(Employee)