Problem with array in Java

Question

I am trying to create a calendar of contacts in java, I am using some classes that were requested in the exercise.

the main class:

    import java.util.Scanner;

    public class Lista15Q03 {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);

        int max = 3;

        Endereco end[] = new Endereco[max];

        Telefones tel[] = new Telefones[max];

        Emails email[] = new Emails[max];

        Contatos con[] = new Contatos[max];
        Contatos c = new Contatos();
        c.setEndereco(end);

        int op;
        int indice = 0;

        do {

            System.out.println("1 - adicionar");
            System.out.println("2 - listar");
            System.out.println("3 - mostrar");
            System.out.println("4 - alterar");
            System.out.println("5 - apagar");
            System.out.println("6 - sair");
            System.out.print("escolha: ");
            op = scan.nextInt();

            switch(op){
                case 1:
                    if(indice < max){

                        c = new Contatos();

                        System.out.println("nome: ");
                        String nome = scan.next();
                        c.setNome(nome);

                        System.out.print("nome da rua: ");
                        String rua = scan.next();
                        end[indice].setRua(rua);

                        System.out.print("número: ");
                        String num = scan.next();
                        end[indice].setNumero(num);

                        System.out.print("bairro: ");
                        String bairro = scan.next();
                        end[indice].setRua(bairro);

                        con[indice] = c;
                        indice++;
                    }else{
                        System.out.println("");
                        System.out.println("lista de contatos cheia");
                        System.out.println("");
                    }
                    break;
                case 2:
                    break;
                case 6:
                    break;
                default:
                    System.out.println("opção inválida");
            }

        } while (op != 6);

    }

}

the class of contacts:

public class Contatos {
    private String nome;
    private Endereco[] endereco;
    private Emails[] email;
    private Telefones[] telefones;

    public String getNome() {
        return nome;
    }

    public void setNome(String nome) {
        this.nome = nome;
    }

    public Endereco[] getEndereco(){
        return endereco;
    }

    public void setEndereco(Endereco[] endereco){
        this.endereco = endereco;
    }

    public Emails[] getEmail() {
        return email;
    }

    public void setEmail(Emails[] email) {
        this.email = email;
    }

    public Telefones[] getTelefones() {
        return telefones;
    }

    public void setTelefones(Telefones[] telefones) {
        this.telefones = telefones;
    }

}

error running on terminal:

Exception in thread "main" java.lang.Nullpointerexception At lista15q03.main(Lista15q03.java:46)

error running in netbeans:

Exception in thread "main" java.lang.NullPointerException
    at lista15q03.Lista15Q03.main(Lista15Q03.java:41)
/home/henrique/.cache/netbeans/8.2/executor-snippets/run.xml:53: Java returned: 1
FALHA NA CONSTRUÇÃO (tempo total: 5 segundos)

Answer 1

Missing you instantiate the objects in the arrays positions end[], tel[], email.

On calls

Endereco end[] = new Endereco[max];

Telefones tel[] = new Telefones[max];

Emails email[] = new Emails[max];

Only the array of each of these objects with operator were instantiated new.

For each array vc needs a for that traverses the entire array instantiating the objects

As in the example below

  for (int i = 0; i < max; i++) {
            end[i] = new Endereco();
        }

However, I note that the objects Addressee, Emails, and Phones are already class attributes Contacts. In this way, a more correct way would be to remove them from the main class and add a method for initializing these objects in their own classes. As in the example below.

public class Contatos {

    int max;
    private String nome;
    private Endereco[] endereco;
    private Emails[] email;
    private Telefones[] telefones;

    public Contatos(int max) {
        this.max = max;
        initEnderecos();
   }

    public String getNome() {
        return nome;
   }

    public void setNome(String nome) {
        this.nome = nome;
   }

    public Endereco[] getEndereco() {
       return endereco;
   }

    public void setEndereco(Endereco[] endereco) {
        this.endereco = endereco;
  }

    public Emails[] getEmail() {
        return email;
  }

    public void setEmail(Emails[] email) {
       this.email = email;
  } 

    public Telefones[] getTelefones() {
       return telefones;
  }

   public void setTelefones(Telefones[] telefones) {
      this.telefones = telefones;
  }

   private void initEnderecos() {
        for (int i = 0; i < max; i++) {
            this.endereco[i] = new Endereco();
        }
   }
} 

In this example I moved the attribute max, which is the maximum size of the contact list for the class Contato and initialize only the array of Endereco. The other vc can do similarly.

Note that, this is just one of the improvements you can make in this code

Answer 2

Hello, the problem that is happening is that it was just declaring the value for array as new Address, however each item of it is null until initialized, so you will have to do this initialization before adhering values to the variables of this object.

 switch(op){
             case 1:
                 if(indice < max){

                     end[indice] = new Endereco();
                     c = new Contato();

                     System.out.println("nome: ");
                     String nome = scan.next();
                     c.setNome(nome);

                     System.out.print("nome da rua: ");
                     String rua = scan.next();
                     end[indice].setRua(rua);

                     System.out.print("número: ");
                     String num = scan.next();
                     end[indice].setNumero(num);

                     System.out.print("bairro: ");
                     String bairro = scan.next();
                     end[indice].setBairro(bairro);

                     c.setEndereco(end);
                     con[indice] = c;
                     indice++;
                 }

Another thing that I noticed by analyzing your code is that arrow an address in object c, however dps initializes it again, losing what was set that in the case had nothing, the most correct thing to do is just put this value after entering all the items of the address, and tbm was putting the value of the neighborhood on the street.

Answer 3

If I may use List, do that you will be happier, if you cannot, you will have to create an object for each Array you created, because each position of the Array is waiting for an object and you are passing a String. then in your case it would look like this.

BS: I will do only with one of the Array and you replicate.

Endereco []end = new Endereco[max]; // cada posição tem que ser um objeto
Endereco endereco = new Endereco();

System.out.print("nome da rua: ");
String rua = scan.next();
endereco.setRua(rua);
end[indice] = endereco;

end[indice].getRua(); //para mostrar o valor depois.