比较器实施

Question

I am having a problem with understanding and using the Comparator I have been asked the following:

Create a CompanyDataBase class.

public java.util.ArrayList sortByName() You'll need to use a Comparator object for this.

I have written this method in the class.

     @Override
   public int sortByName(Employee name1, Employee name2)
   {
      return (int) (name1.super.getName() - name2.super.getName());   
   }

And this seperate Comparator class:

import java.util.*;

public class EmployeeNameComparator implements Comparator<Employee> 
{


   public int compare(Employee first, Employee second)
   {
      return (int) (first.super.getName() - second.super.getName());
   }

}

But I obviously wont be using the same "return (int) (name1.super.getName() - name2.super.getName());" line of code in both classes...but I have no idea how to implement it in the sortByName method.

I am using a compareTo Comparator interface in a separate Employee class to invoke an overloaded use of the Comparator object.

Any help, suggestions, lines of code would be really appreciated!!

Answer 1

Strings aren't primitives and can't use subtraction.

Use the Comparable interface of strings to do this work

public int compare(Employee first, Employee second)
{
    return first.getName().compareTo(second.getName());
}

Answer 2

You are comparing two Strings ... so you can (if they are not null) do this:

name1.compareTo(name2);

Now you need to take nulls into account ... so your comparator would look something like this:

public class EmployeeNameComparator implements Comparator<Employee> 
{
   public int compare(Employee first, Employee second)
   {
      if (first != null && second != null) {
           if (first.getName() != null) {
               return first.getName().compareTo(second.getName());
           }
      }
.. other cases here


   }
}