Java address book. How to prevent duplicate contacts in my code?

Question

switch(menuChoice) {

case 1: 
    System.out.println(\"Enter your contact\'s first name:\\n\");
    String fname = scnr.next();
    System.out.println(\"Enter your cont         


        

Answer 1

You could simply use HashSet and avoid any kind of loops to test it. HashSet is in charge of this function.

import java.util.Set;
import java.util.HashSet;

public class AddressBook {

   Set<Person> listOfContacts = new HashSet<>();

   public void addContact(Person p) {
      if (!listOfContacts.add(p))
         System.out.println("Sorry this contact already exists.");    
   }
}            

To increment ID property you should have 2 properties, 1 static and another one, and increment it in constructor. Look:

public class Person {
   private final int ID;
   private static int id = 1000;
   private String fName;
   private String lName;

   public Person(String fName, String lName) {       // Constructor I'm using to try and increment the ID each time a Person object is created starting at 1001.
      this.ID= ++id;
      this.fName = fName;
      this.lName = lName;   
   } 

To make the HashSet not accept duplicate objects you should set which properties should not be duplicated in the class (Person in your case). Follows an example:

   @Override
   public int hashCode() {
      int hash = 7;
      hash = 61 * hash + Objects.hashCode(this.fName);
      hash = 61 * hash + Objects.hashCode(this.lName);
      return hash;
   }

   @Override
   public boolean equals(Object obj) {
      if (obj == null || getClass() != obj.getClass())
         return false;

      final Person other = (Person) obj;
      if (!Objects.equals(this.fName, other.fName))
         return false;

      return Objects.equals(this.lName, other.lName);
   }
}

By the way, you can generate equals and hashCode methods using your IDE (Eclipse, NetBeans, etc.)

EDIT

Since you aren't able to use HashSet, I will show a version with ArrayList. By the way, you have to use HashCode and equals as I said to make it work well

import java.util.List;
import java.util.ArrayList;

public class AddressBook {

   List<Person> arrayOfContacts = new ArrayList<>();

   public void addContact(Person p) {
      if (listOfContacts.contains(p))
         System.out.println("Sorry this contact already exists.");

      else
         arrayOfContacts.add(p);    
   }
}

Answer 2

You should Override equals inside your Person class

public boolean equals(Object obj) {
    if(fName.equals(obj.getfName()) && lName.equals(obj.getlName)) {
        return true;
    }
    return false;
}

Then just call:

if(!(person1.equals(person2))) {
//not a duplicate
}

And of course substitute the variables/objects with whatever objects you want. You also should add getters and setters for last and first name. Hope this helps!

Answer 3

Here is the code for keeping out duplicate ID's.

public void addContact(Person p) {

    for(int i = 0;  i < ArrayOfContacts.size(); i++) {
        Person contact = ArrayOfContacts.get(i);
        if(contact.getID() == p.getID()) {
            System.out.println("Sorry this contact already exists.");
            return; // the id exists, so we exit the method. 
        }
    }

    // Otherwise... you've checked all the elements, and have not found a duplicate
    ArrayOfContacts.add(p);

}

If you would like to change this code to keep out duplicate names, then do something like this

public void addContact(Person p) {
    String pName = p.getFname() + p.getLname();
    for(int i = 0;  i < ArrayOfContacts.size(); i++) {
        Person contact = ArrayOfContacts.get(i);
        String contactName =  contact.getFname() + contact.getLname(); 
        if(contactName.equals(pName)) {
            System.out.println("Sorry this contact already exists.");
            return; // the name exists, so we exit the method. 
        }
    }

    // Otherwise... you've checked all the elements, and have not found a duplicate
    ArrayOfContacts.add(p);

}

Answer 4

Use a HashSet. For every user's name, add it to the HashSet.

For example:

HashSet<String> namesUsed = new HashSet<String>();

if (namesUsed.contains(userName)) {
    //do what you want here, if this is entered it means there is a duplicate
} else {
    namesUsed.add(userName); //add it to the list of used names
}