Arraylike NullPointerException

[annfarrell32]

Hi,
I am currently taking Java II because I want to. Unfortunately, the teacher isn't the best and neither is the book. I'm getting a NullPointerException when adding a contact to the arraylist ContactDatabase. I would just like to know what I'm overlooking so I can correct and continue with this lesson. I know the Contact is not being instantiated, but am at a lost for what I'm doing wrong. I appreciate any and all help. Thanks Annie.

Here's the code.

/**
* ContactDatabase.java
*
* This program implements a database of contacts that can be
* added to, searched, displayed, or items removed. An ArrayList
* is used to store the database.
*
* Created: Sun Apr 3 2005
* Updated: Sun July 30 2006 Amy Hickey
*
* @author Kenrick Mock
* @version 1
*
*/

import java.util.Scanner;
import java.util.ArrayList;

/**
* The Contact class stores the details for a single contact. There is no error
* checking on any of the input. Whatever string is passed in for a given
* attribute is accepted.
*/
class Contact
{
private String first, last, phone, email;

/**
* Constructors.
*/
public Contact()
{

}

public Contact(String first, String last, String phone, String email)
{
this.first = first;
this.last = last;
this.phone = phone;
this.email = email;
}

/*
* Accessor Methods
*/

public String getFirst()
{
return first;
}

public String getLast()
{
return last;
}

public String getPhone()
{
return phone;
}

public String getEmail()
{
return email;
}

/*
* Mutator Methods
*/
public void setFirst(String first)
{
this.first = first;
}

public void setLast(String last)
{
this.last = last;
}

public void setPhone(String phone)
{
this.phone = phone;
}

public void setEmail(String em)
{
this.email = em;
}



/*
* Return all fields concatenated into a string
*/
public String toString()
{
return last + ", " + first + ". " + phone + ", " + email;
}


public boolean equals(Object otherObject)
{
if (otherObject ==null)
{
return false;
}
else if (getClass() != otherObject.getClass())
{
return false;
}
else
{
Contact otherContact = (Contact)otherObject;
return (first.equals(otherContact.first) &&
last.equals(otherContact.last)&&
phone.equals(otherContact.phone)&&
email.equals(otherContact.email));
}
}

}


/**
* The ContactDatabase class stores each contact in an arraylist.
* Methods exist to add new contacts, search contacts, delete, and print contacts
* to the console.
*/
public class ContactDatabase
{
private ArrayList<Contact> contacts; // ArrayList of contact
private static final int QUIT = 0; // Menu choices
private static final int ADD = 1;
private static final int LISTALL = 2;
private static final int SEARCH = 3;
private static final int DELETE = 4;

/**
* Default constructor - make a new ArrayList object with parameter type Contact
*/
public void createContactDatabase()
{
contacts = new ArrayList<Contact>();

}

/**
* inputContact inputs contact information from the keyboard.
* It then stores this new contact in the contacts ArrayList.
*/
public void inputContact()
{
Contact myContact;

Scanner input = new Scanner(System.in);

System.out.println("Enter the first name of a the person you wish to add, ie Karen");
String first = input.nextLine();

System.out.println("Enter the last name of a the person you wish to add, ie Brown");
String last = input.nextLine();

System.out.println("Enter your contact's phone number.");
String phone = input.nextLine();

System.out.println("Enter your contact's email address.");
String email = input.nextLine();

myContact = new Contact(first, last, phone, email);
contacts.add(myContact);


System.out.println("The contacts details are:");
System.out.println(contacts);
}


/**
* displayAll iterates through the ArrayList of contacts and outputs each one
* to the screen.
*/
public void displayAll()
{
System.out.println("The contacts list contains:");
for (Contact entry : contacts)
System.out.println (entry);
}

/**
* displayMatch inputs a keyword from the user.
* It then iterates through the ArrayList of contacts and outputs each one
* to the screen if the contact information contains the keyword.
*/
public void displayMatch()
{
int locationIndex = contacts.indexOf("first");
System.out.println("Index location of the String \"Jeff\" is: " + locationIndex);

}

/**
* deleteMatch inputs a keyword from the user.
* It then iterates through the ArrayList of contacts and asks the user
* if the contact should be deleted, if the contact information contains the keyword.
*/
public void deleteMatch()
{

}

// Main class
public static void main(String[] args)
{
ContactDatabase cdb = new ContactDatabase();
Scanner scan = new Scanner(System.in);
int choice = ADD;

// Main menu
while (choice != QUIT)
{
System.out.println();
System.out.println("Choose from the following:");
System.out.println("0) Quit");
System.out.println("1) Add new contact");
System.out.println("2) List all contacts");
System.out.println("3) Search contacts by keyword and display");
System.out.println("4) Search contacts by keyword and remove");
choice = scan.nextInt();
switch (choice)
{
case ADD: cdb.inputContact();
break;
case LISTALL: cdb.displayAll();
break;
case SEARCH: cdb.displayMatch();
break;
case DELETE: cdb.deleteMatch();
break;
}
}
}
} // ContactDatabase

[RedSon]

Why do you have this method: createContactDatabase()?

[Ganon11]

So that's it!

You have the method createContactDatabase(), but from your documentation, this should be a constructor! Rename it as public ContactDatabase(), and when you create the object in main(), it will create its own Arraylist and get rid of the NullPointerException.

[r035198x]

Hi,
I am currently taking Java II because I want to. Unfortunately, the teacher isn't the best and neither is the book. I'm getting a NullPointerException when adding a contact to the arraylist ContactDatabase. I would just like to know what I'm overlooking so I can correct and continue with this lesson. I know the Contact is not being instantiated, but am at a lost for what I'm doing wrong. I appreciate any and all help. Thanks Annie.

Here's the code.

/**
* ContactDatabase.java
*
* This program implements a database of contacts that can be
* added to, searched, displayed, or items removed. An ArrayList
* is used to store the database.
*
* Created: Sun Apr 3 2005
* Updated: Sun July 30 2006 Amy Hickey
*
* @author Kenrick Mock
* @version 1
*
*/

import java.util.Scanner;
import java.util.ArrayList;

/**
* The Contact class stores the details for a single contact. There is no error
* checking on any of the input. Whatever string is passed in for a given
* attribute is accepted.
*/
class Contact
{
private String first, last, phone, email;

/**
* Constructors.
*/
public Contact()
{

}

public Contact(String first, String last, String phone, String email)
{
this.first = first;
this.last = last;
this.phone = phone;
this.email = email;
}

/*
* Accessor Methods
*/

public String getFirst()
{
return first;
}

public String getLast()
{
return last;
}

public String getPhone()
{
return phone;
}

public String getEmail()
{
return email;
}

/*
* Mutator Methods
*/
public void setFirst(String first)
{
this.first = first;
}

public void setLast(String last)
{
this.last = last;
}

public void setPhone(String phone)
{
this.phone = phone;
}

public void setEmail(String em)
{
this.email = em;
}



/*
* Return all fields concatenated into a string
*/
public String toString()
{
return last + ", " + first + ". " + phone + ", " + email;
}


public boolean equals(Object otherObject)
{
if (otherObject ==null)
{
return false;
}
else if (getClass() != otherObject.getClass())
{
return false;
}
else
{
Contact otherContact = (Contact)otherObject;
return (first.equals(otherContact.first) &&
last.equals(otherContact.last)&&
phone.equals(otherContact.phone)&&
email.equals(otherContact.email));
}
}

}


/**
* The ContactDatabase class stores each contact in an arraylist.
* Methods exist to add new contacts, search contacts, delete, and print contacts
* to the console.
*/
public class ContactDatabase
{
private ArrayList<Contact> contacts; // ArrayList of contact
private static final int QUIT = 0; // Menu choices
private static final int ADD = 1;
private static final int LISTALL = 2;
private static final int SEARCH = 3;
private static final int DELETE = 4;

/**
* Default constructor - make a new ArrayList object with parameter type Contact
*/
public void createContactDatabase()
{
contacts = new ArrayList<Contact>();

}

/**
* inputContact inputs contact information from the keyboard.
* It then stores this new contact in the contacts ArrayList.
*/
public void inputContact()
{
Contact myContact;

Scanner input = new Scanner(System.in);

System.out.println("Enter the first name of a the person you wish to add, ie Karen");
String first = input.nextLine();

System.out.println("Enter the last name of a the person you wish to add, ie Brown");
String last = input.nextLine();

System.out.println("Enter your contact's phone number.");
String phone = input.nextLine();

System.out.println("Enter your contact's email address.");
String email = input.nextLine();

myContact = new Contact(first, last, phone, email);
contacts.add(myContact);


System.out.println("The contacts details are:");
System.out.println(contacts);
}


/**
* displayAll iterates through the ArrayList of contacts and outputs each one
* to the screen.
*/
public void displayAll()
{
System.out.println("The contacts list contains:");
for (Contact entry : contacts)
System.out.println (entry);
}

/**
* displayMatch inputs a keyword from the user.
* It then iterates through the ArrayList of contacts and outputs each one
* to the screen if the contact information contains the keyword.
*/
public void displayMatch()
{
int locationIndex = contacts.indexOf("first");
System.out.println("Index location of the String \"Jeff\" is: " + locationIndex);

}

/**
* deleteMatch inputs a keyword from the user.
* It then iterates through the ArrayList of contacts and asks the user
* if the contact should be deleted, if the contact information contains the keyword.
*/
public void deleteMatch()
{

}

// Main class
public static void main(String[] args)
{
ContactDatabase cdb = new ContactDatabase();
Scanner scan = new Scanner(System.in);
int choice = ADD;

// Main menu
while (choice != QUIT)
{
System.out.println();
System.out.println("Choose from the following:");
System.out.println("0) Quit");
System.out.println("1) Add new contact");
System.out.println("2) List all contacts");
System.out.println("3) Search contacts by keyword and display");
System.out.println("4) Search contacts by keyword and remove");
choice = scan.nextInt();
switch (choice)
{
case ADD: cdb.inputContact();
break;
case LISTALL: cdb.displayAll();
break;
case SEARCH: cdb.displayMatch();
break;
case DELETE: cdb.deleteMatch();
break;
}
}
}
} // ContactDatabase

Please use code tags when posting code.
Also find time to read this.

[annfarrell32]

Please use code tags when posting code.
Also find time to read this.

Thanks, I never stopped to think about correcting the code that was provided. Just assumed it would be correct. You learn something new everyday.
Thanks again,
Annie

[RedSon]

The code above is correct it just follows poor programming practices.