提供接口的方法而不是在java中实现接口

Question

我正在阅读有关 Java 接口的内容。提到我们必须实现compareTo方法来调用ArrayList容器上的“排序”，例如Employee类应该实现Comparable接口。

稍后解释了为什么Employee类不能简单地提供“compareTo”方法而不实现Comparable接口？ 接口的原因是 Java 编程是强类型的。当进行方法调用时，编译器需要能够检查该方法是否确实存在。

因此，当我不实现“Comparable 接口并使用 Arrays.sort 方法时，我预计会出现编译时错误，但我没有观察到编译错误，而是出现运行时错误。请解释为什么上面的场景中没有显示编译时错误

下面是代码片段

package com.vrk.inheritance;

import java.time.*;
import java.util.Arrays;

public class Employee
{
   private String name;
   private double salary;
   private LocalDate hireDay;

   public Employee(String name, double salary, int year, int month, int day)
   {
      this.name = name;
      this.salary = salary;
      hireDay = LocalDate.of(year, month, day);
   }

   public String getName()
   {
      return name;
   }

   public double getSalary()
   {
      return salary;
   }

   public LocalDate getHireDay()
   {
      return hireDay;
   }

   public void raiseSalary(double byPercent)
   {
      double raise = salary * byPercent / 100;
      salary += raise;
   }
   
   /*public int compareTo(Object otherObject) {
       System.out.println("Employee compareTo called");
       return 0;
   }*/
   
   /**
    * equalTo function in employee. Created on 8th Sep 2024
    * @param another object to compare to this object
    */
   public boolean equals(Object otherObject) {
       // quick test to check if objects are identical
       if ( this == otherObject) return true;
       
       // must return false if the explicit parameter is null
       if(otherObject == null) return false;
       
       // if the classes don't match, they can't be equal
       if (getClass() != otherObject.getClass()) return false;
       
       // now we know otherObject is a non-null Employee
       var other = (Employee) otherObject;
       
       // test whether the fields have identical value
       // Not sure in my setup below line is not working, but online compiler it is working. 
       // java.util.Objects.equals(this.hireDay, other.hireDay);
        return true;
   }
   
   public static void main(String[] args) {
       var staff = new Employee[3];

       // fill the staff array with Manager and Employee objects
       staff[0] = new Employee("Harry Hacker", 50000, 1989, 10, 1);
       staff[1] = new Employee("Tommy Tester", 40000, 1990, 3, 15);
       staff[1] = new Employee("Ravi Tester", 60000, 1999, 4, 16);
       Arrays.sort(staff);
   }
}

Answer 1

如果您查看

Arrays.sort

的文档，您会发现它根本不使用泛型；只需要一个

Object[]

。这就是为什么你不会收到编译错误。

这是有历史原因的：该方法是在 Java 引入泛型之前编写的。