I am trying to understand why I get this error Exception in thread "main" java.lang.NullPointerException

interface NavyAviation//interface with two abstract methods
{
   public void NavyAviation();
   public void SearchAndRescue();
}

public class Aircrew//superclass
{
   public void Aircrew()
   {
      System.out.println("Naval Rescue Swimmer(SAR) is the best rate in the Navy");
   }
}


public class AircrewMember//super class with data members, accessor, mutator, and toString methods
{
private String name;
private Date ad;

public AircrewMember()
{
name=" ";
ad=null;
}
public AircrewMember(String name, Date ad)
{
this.name=name;
this.ad=ad;
}
public void setName(String name)
{
this.name=name;
}
public String getName()
{
return name;
}
public String toString()
{
String str="AW's name is " + name + "\nAW's arrival date is: "+ ad.toString();
return str;
}
}


public class AWInfo extends AircrewMember/*subclass with data members, 
accessor, mutator, and toString methods*/

{
private int rate;
final static int AWR_RATE=1;
final static int AWS_RATE=2;
public static final int MAX_RATE=2;
private AircrewMember Aw;


public AWInfo()
{
rate=0;
/*shift=0;*/
Aw=null;
}
public AWInfo(int rate, AircrewMember Aw)//method overloading
{
this.rate=rate;
this.Aw=Aw;
}

public void rate()
{
rate();
}

   public void rate(int rating)throws InvalidRate//exception handeling
   {
   if(rating<0 || rating>MAX_RATE)
   /*(rating != "AWR" || rating != "AWS")*/
   throw new InvalidRate(rating);
   rate=rating;
   }


   /*public void shift()
   {
   shift();
   }
   public void shift(int workShift) throws InvalidShift//exception handeling
   {
   if(workShift<0 || workShift>MAX_SHIFT)
   throw new InvalidShift(workShift);
   shift=workShift;
   }*/

   public int getRate()
   {return rate;}

   /*public int getShfit()
   {return shift;}*/

   public String toString()//method overriding 
   {
   String str= super.toString();
   str+="\nRate: ";
   if(rate==AWR_RATE)
   str+= "AWR";
   if(rate==AWS_RATE)
   str+="AWS";
   return str;
   }
}







public class ProductionWorker extends Employee
{
   final static int DAY_SHIFT=1;
   final static int NIGHT_SHIFT=2;
   public static final int MAX_SHIFT=2;
   private int shift;
   private double payRate;

    public ProductionWorker()
   {
   super();
   shift=0;
   payRate=8.50;
   }
   public ProductionWorker(String name,  Date hd/*, int number, int shift, double payRate*/)
   {
   super(name, /*number,*/ hd);
   /*this.shift=shift;
   this.payRate=payRate;*/
   }

   public void shift()
   {
   shift();
   }
   public void shift(int workShift) throws InvalidShift
   {
   if(workShift<0 || workShift>MAX_SHIFT)
   throw new InvalidShift(workShift);
   shift=workShift;
   }
   public void payRate()
   {
   payRate();
   }
   public void payRate(double newPay)throws InvalidPayRate
   {
   if(newPay<payRate)
   throw new InvalidPayRate(newPay);
   payRate=newPay;
   }

   public int getShift()
   {
   return shift;
   }
   public double getPayRate()
   {
   return payRate;
   }
   public String toString()
   {
   String str= super.toString();

   str +="\nShift: ";
   if (shift == DAY_SHIFT)
   str += "Day";
   else if (shift == NIGHT_SHIFT)
   str += "Night";
   else
   str += "Invalid Shift Number";

   str += "\nHourly Pay Rate: ";
   return str;
   }
}


import java.util.Scanner;
import java.io.*;

public class FreedomFighters extends Aircrew implements NavyAviation
{
public void NavyAviation()
{System.out.println("Enlisted Naval Aviaton");}
public void SearchAndRescue()
{System.out.println("Search and Rescue rates holds the only real AW's");}
public void Aircrew()
{System.out.println("This is for all AWRs and AWSs, all other are not welcomed");}

   public static void main(String[] args)
      {
      FreedomFighters ff1=new FreedomFighters();
      ff1.NavyAviation();
      ff1.SearchAndRescue();
      ff1.Aircrew();

      Scanner keyboard=new Scanner(System.in);
      int payGrade, Ar,rate, idNumber, ws, day, month, year;
      String name;
      AWInfo f1=new AWInfo();

      try
      {

      System.out.println("Enter 1 for AWR or 2 for AWS: ");
      Ar=keyboard.nextInt();
      f1.rate(Ar);}
      catch(InvalidRate e){
      System.out.println(e.getMessage());
      System.exit(0);}

      /*try{
      System.out.println("Enter 1 for morning shift or 2 for evening shift");
      ws=keyboard.nextInt();
      f1.shift(ws);
      }

       catch(InvalidShift e)
      {System.out.println(e.getMessage());}*/

      System.out.println();
      keyboard.nextLine();

      System.out.print("Enter new AW's name: ");
      name = keyboard.nextLine();

      System.out.print("Enter AW's arrival day: ");
      day = keyboard.nextInt();

      System.out.print("Enter AW's arrival month: ");
      month = keyboard.nextInt();

      System.out.print("Enter AW's arrival year: ");
      year = keyboard.nextInt();

      Date ad = new Date(day, month, year);

      AircrewMember a1 = new AircrewMember(name, ad);//aggregation

      System.out.println(f1.toString());//aggregation

    }
 }