Error variable not initialized...Why?

import java.util.*;
public class lab9
{
   public static void main(String args[])
   {
      Scanner input = new Scanner( System.in );
      final double BONUS0 = 0.0;
      final double BONUS1 = 25.0;
      final double BONUS2 = 50.0;
      final double BONUS3 = 100.0;
      final double BONUS4 = 200.0;
      System.out.println("Enter employee's first name:");
      String firstName;
      System.out.println("Enter employee's last name:");
      String lastName;
      System.out.println("Enter this year's units:");
      int unitsThisYear;
      System.out.println("Enter last year's units:");
      int unitsLastYear;
      double bonus;
       {
         if ((unitsThisYear > unitsLastYear) && (unitsThisYear < 1000))
         {
            bonus = BONUS1;
            System.out.println("Bonus is $" +bonus);
         }
         else if ((unitsThisYear > unitsLastYear) && (unitsThisYear > 1001) && (unitsThisYear < 3000))
         {
            bonus = BONUS2;
            System.out.println("Bonus is $" +bonus);
         }
         else if ((unitsThisYear > unitsLastYear) && (unitsThisYear > 3001) && (unitsThisYear < 6000))
         {
            bonus = BONUS3;
            System.out.println("Bonus is $" +bonus);
         }
         else if ((unitsThisYear > unitsLastYear) && (unitsThisYear > 6001))
         {
            bonus = BONUS4;
            System.out.println("Bonus is $" +bonus);
         }
         else 
         {
            bonus = BONUS0;
            System.out.println("Bonus is $" +bonus);
         }
      }
   }//end main
}//end class   

I kept getting an error of else without if but i manages to fix it but now I'm getting the error of not initializing the varible. I dont understand why it keeps saying that the variable unitsThisYear and unitsLastYear are not initialzed. I thought I initialized it with the lines: int unitsThisYear; int unitsLastYear;

lab9.java:25: error: variable unitsThisYear might not have been initialized
         if ((unitsThisYear > unitsLastYear) && (unitsThisYear < 1000))
              ^
lab9.java:25: error: variable unitsLastYear might not have been initialized
         if ((unitsThisYear > unitsLastYear) && (unitsThisYear < 1000))
                              ^