How to implement a check?

Question

Greetings friends. I started learning Java not so long ago and would appreciate some help.

I have a Person class with the variables firstName , secondName and lastName .

There is a class AdressBook in which ArrayList<Person> . In this sheet I add 3 Person 's.

There is also an addPerson method that simply adds a new Person to the collection.

I need to supplement this method so that before adding it is checked: is there a Person with such a full name ( firstName , secondName and lastName ) or not.

Help to implement the method correctly. Unfortunately, my check fails, and the cycle in which I iterate over the collection does not end. Surely children's mistakes, but nonetheless ++ you in karma).

 public class Main { public static void main(String[] args) { AdressBook contact = new AdressBook(); Adress a1 = new Adress("Russia", "Voronezhskaya obl.", "Voronezh", "Prospekt Truda", "2B", 394006, "31"); Adress a2 = new Adress("Russia", "Moskovskaya obl.", "Korolev", "Prospekt Kosmonavtov", "8A", 632008, "35/2"); Adress a3 = new Adress("Israel", "Tel-aviv.", "Petah Tikva", "Shpritsek", "14", 123478, "12"); Person p1 = new Person("Ivan", "Ivanovich", "Ivanov", 15, true, "89155473197", a1); Person p2 = new Person("Petr", "Petrovich", "Petrov", 59, true, "89998217516", a2); Person p3 = new Person("Sidor", "Sidorovich", "Sidorov", 27, true, "85241325698", a3); contact.book.add(p1); contact.book.add(p2); contact.book.add(p3); contact.addPerson2(p1); } }

 public class AdressBook { public ArrayList<Person> book = new ArrayList<>(); public void addPerson2(Person person) { for (int i = 0; i < book.size();i++ ) { if (person.firstName.equals(book.get(i).firstName) && person.secondName.equals(book.get(i).lastName) && person.lastName.equals(book.get(i).lastName)){ System.out.println("Такой контакт уже существует."); } else { book.add(person); } } }

 public class Person { String firstName; String secondName; String lastName; int age; boolean gender; String phone; Adress ad; public Person(String firstName, String secondName, String lastName, int age, boolean gender, String phone, Adress ad) { this.firstName = firstName; this.secondName = secondName; this.lastName = lastName; this.age = age; this.gender = gender; this.phone = phone; this.ad = ad; } }

Accepted Answer · 2016-10-29T17:40:32

You have an error in the addPerson2 method in comparison:
if ... && person.secondName.equals(book.get(i).lastName) && ... -
secondName compare with lastName
Passing through the list in a loop, you do not need to add, you only need to check, and if you find a duplicate, swear and exit (you can simply return). It is not necessary to add at every check inside the cycle, but only when the entire list has passed and made sure that there is no duplicate — that is, after the cycle.
That is, the body of the method should look like this (short diagram):
```
 for (Person p: list) 
   if (p.isTheSameThat (newPerson)) {
     System.out.println ("Do not roll!");  return;
   }
 list.add (newPerson); 
```
And yes, by the way, it will be more elegant to implement a match check as a class method.

vokhm, thank you very much) eyes zamylilsya =) All corrected.
And how to take a collection object to compare its fields with the fields of a new object in the case of the absence of the index i, and using not for but foreach?
In Java, there is no foreach ; the form is used for (<type> <var>: <collection>) , as I wrote in the response in the second code fragment.
This code is literal, you can compile it, if you define the isTheSameThat() comparison method in the Person class.
The variable p in this example in turn receives the values of all the elements of the list in turn - this will be the next collection object that should be compared with the new one.
And in the case of extraction by the index ( list.get(i) ) and iteration (as I wrote), the comparison can be made in the forehead, as you have done, and in a separate special method.

How to implement a check?

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