Question

Fix the following null pointer error.

import java.util.*;

import java.io.*;

public class PhoneBook {

public static void main(String[]args)throws IOException {

PhoneBook obj = new PhoneBook();

PhoneContact[]phBook = new PhoneContact[20];

Scanner in = new Scanner(System.in);

obj.acceptPhoneContact(phBook,in);

PrintWriter pw = new PrintWriter("out.txt");

obj.displayPhoneContacts(phBook,pw);

pw.close();

}

public void acceptPhoneContact(PhoneContact[]phBook, Scanner k) { //void function that takes in the parameters

//phBook array and the scanner so the user can input the information

//declaring these variables

String fname = "";

String lname = "";

String contact = "";

String option = "";

System.out.println("Do you have any new contacts to enter? Enter zzz to exit. ");

option = k.next(); //enter yes or no and the output is stored in the option variable

int count = 0; //initialize count to 0

if(phBook[0] != null) { //this checks if the phBook is empty or not

count = getCurrentContactCount(phBook); //if yes, it will display an integer and value assigned to count

}

else {//if not, the phone book is empty and a message will be displayed saying that its empty

System.out.println("Phone book is empty");

count = 0;

}

while(!(option.contentEquals("zzz")) && count <= 20) { //while loop that will continue to ask

//the user for more contacts if there are not 20 contacts already and if the user does not enter zzz

System.out.println("Enter first name: ");

fname = k.next(); //after entering in the name; it stores it in the fname variable

System.out.println("Enter last name: ");

lname = k.next();

System.out.println("Enter phone number: ");

contact = k.next();

if(option.contentEquals("zzz")) {

break;

}

if(phBook[0] != null) { //if this is not empty it will look for a contact

if(searchContact(phBook, fname, lname, contact) != null) {//if this is not empty, it'll say the contact exists

System.out.println("Contact exists");

System.out.println(searchContact(phBook, fname, lname, contact));

break;

}else {//otherwise it will add the contact to the phone book

phBook[count] = new PhoneContact(fname, lname, contact);

count++;

if(count >= 20) {

System.out.println("You have reached the maximum number of contacts.");

break;

}

}

}

else {//if the phone book array is empty then it will print that the phone book is empty and add the contact

System.out.println("Phone book is empty");

phBook[count] = new PhoneContact(fname, lname, contact);

count++;

}

System.out.println("Do you have any new contacts to enter? ");

option = k.next();

}//ends while loop; if the user wants to exit and no longer enter in contacts they will type zzz

System.out.println("The phone book has " + count + " contacts");

}

public int getCurrentContactCount(PhoneContact[]phBook) {

int numContacts = 0;

for(int a = 0; a < phBook.length; a++) {

if(phBook[a] != null) {

numContacts++;

}

}

return numContacts;

}

public PhoneContact searchContact(PhoneContact[]phBook, String fname, String lname, String phone) {

PhoneContact contact= null;

for(int a= 0 ; a < phBook.length ; a++) {

if(phBook[a] != null && phBook[a].getfirstName().equals(fname)) {//compare lname and phone contact

System.out.println("Phone book conatct exists");

contact = phBook[a];

break;

}

}

return contact;

}

public void displayPhoneContacts(PhoneContact[]phBook, PrintWriter pw)

throws IOException{

pw.println("Phone Book");

pw.println("**************************");

pw.print("First Name\tLast Name\t Contact number");

for(int a= 0 ; a < phBook.length ; a++) {

pw.println(phBook[a].getfirstName() +"\t" + phBook[a].getlastName()+"\t" + phBook[a].getphoneNumber());

}

}

}

Answer 1

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

class PhoneContact{
   String fname,lname,phoneNum;
   PhoneContact(String f,String l,String c){
       this.fname=f;
       this.lname=l;
       this.phoneNum=c;
   }
   public String getFname() {
       return fname;
   }
   public void setFname(String fname) {
       this.fname = fname;
   }
   public String getLname() {
       return lname;
   }
   public void setLname(String lname) {
       this.lname = lname;
   }
   public String getPhoneNum() {
       return phoneNum;
   }
   public void setPhoneNum(String phoneNum) {
       this.phoneNum = phoneNum;
   }
   public String getfirstName() {
       return this.fname;
   }
   public String getlastName() {
       return this.lname;
   }
   public String getphoneNumber() {
       return this.phoneNum;
   }
}

public class PhoneBook {

   public static void main(String[]args)throws IOException {

       PhoneBook obj = new PhoneBook();

       PhoneContact[]phBook = new PhoneContact[20];

       Scanner in = new Scanner(System.in);
       obj.acceptPhoneContact(phBook,in);
       PrintWriter pw = new PrintWriter("out.txt");

       obj.displayPhoneContacts(phBook,pw);
       pw.close();

   }
   public void acceptPhoneContact(PhoneContact[]phBook, Scanner k) { //void function that takes in the parameters

           //phBook array and the scanner so the user can input the information
           //declaring these variables

           String fname = "";
           String lname = "";
           String contact = "";
           String option = "";
           int count = 0;
          
           System.out.print("Do you have any new contacts to enter(yes)? Enter zzz to exit: ");
           option = k.nextLine();
           while(!(option.contentEquals("zzz")) && count < 20) { //while loop that will continue to ask

               //the user for more contacts if there are not 20 contacts already and if the user does not enter zzz
               System.out.print("Enter first name: ");
               fname = k.nextLine(); //after entering in the name; it stores it in the fname variable
               System.out.print("Enter last name: ");
               lname = k.nextLine();
               System.out.print("Enter phone number: ");
               contact = k.nextLine();
              
               if(phBook[0] != null) { //if this is not empty it will look for a contact

                   if(searchContact(phBook, fname, lname, contact) != null) {//if this is not empty, it'll say the contact exists
                       System.out.println("Contact exists");
                   }else {//otherwise it will add the contact to the phone book
                       phBook[count] = new PhoneContact(fname, lname, contact);
                       count++;
                       if(count >= 20) {
                           System.out.println("You have reached the maximum number of contacts.");
                           break;
                       }
                   }
               }else {//if the phone book array is empty then it will print that the phone book is empty and add the contact
                   if(count==0)
                       System.out.println("Phone book is empty");
                   phBook[count] = new PhoneContact(fname, lname, contact);
                   count++;
               }
               System.out.print("\nDo you have any new contacts to enter(yes)?Enter zzz to exit: ");
               option = k.nextLine();
           }//ends while loop; if the user wants to exit and no longer enter in contacts they will type zzz
           System.out.println("The phone book has " + count + " contacts");
   }
   public int getCurrentContactCount(PhoneContact[]phBook) {
       int numContacts = 0;
       for(int a = 0; a < phBook.length; a++) {
           if(phBook[a] != null) {
               numContacts++;
           }
       }
       return numContacts;
   }
  
   public PhoneContact searchContact(PhoneContact[]phBook, String fname, String lname, String phone) {
       PhoneContact contact= null;
       int n=getCurrentContactCount(phBook);
       for(int a= 0 ; a < n ; a++) {
           if( phBook[a].getfirstName().equalsIgnoreCase(fname) &&
                   phBook[a].getlastName().equalsIgnoreCase(lname) &&
                   phBook[a].getPhoneNum().equalsIgnoreCase(phone)) {//compare lname and phone contact
               System.out.println("Phone book conatct exists");
               contact = phBook[a];
               break;
           }
       }
       return contact;
   }
  
   public void displayPhoneContacts(PhoneContact[]phBook, PrintWriter pw)
           throws IOException{
               int n=getCurrentContactCount(phBook);
               pw.println("Phone Book");
               pw.println("**************************");
               pw.print("First Name\tLast Name\t Contact number");
               for(int a= 0 ; a < n ; a++) {
                   pw.println(phBook[a].getfirstName() +"\t" + phBook[a].getlastName()+"\t" + phBook[a].getphoneNumber());
               }
   }
}

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OUTPUT
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