Boolean help

Hi

I have an arrayList and i must use a method.

Code:

---

/**
    * Method to add a student to the lis, but can't be added if the number (id) already exist.
    * Methos return true if the student is added or false
    *
    * @param  aluno  student to be added
    * @return  True if added
    */
    public boolean addAluno(Aluno aluno)
    {
        boolean estado = false;
        for(int i=0; i<alunos.size(); i++)
        {
           
            if(aluno(Aluno.getID))
            {
                return false;
            }
     
      }
      alunos.add(aluno);
      return true;
    }

---

Class Aluno

Code:

---

public class Aluno
{
    private int id; // Nº do aluno (identificador único)
    private String nome; // Nome do aluno

    /**
    * Construtor dos objectos da classe Aluno
    */
    public Aluno(String nome, int ID)
    {
        this.nome=nome;
        this.id=ID;
    }

    /**
    * Definir métodos de acesso e de mutação para os campos,
    * considerando que o nº de aluo não pode ser alterado
    * getID, getNome, setNome
    */
   
    //Dá o nome do aluno em causa
    public String getNome()
    {
        return nome;
    }
 
    //Vai dar quantos ID estão registados
    public int getID()
    {
        return id;
    }
   
    //Mudança de nome por mutação
    public void SetNome( String name)
    {
        nome = name;
    } 
}

---

The getID method is situated in another class, i have an error saying, canno't find symbol getID..

any help please?

Thanks

You have to use an instance of Aluno to get to the getID() method. Right now you're referring to the whole class, which doesn't make sense. Also, you seem to be trying to use an aluno() method, which I don't see at all.

Thanks for your answer

Well, i'm lost

Code:

---


public boolean addAluno(Aluno aluno)
    {
        boolean estado = false;
       
        Aluno t = new Aluno();
        for(int i=0; i<alunos.size(); i++)
        {

     
      }
      alunos.add(aluno);
      return true;
    }

---

Error saying

found no arguments in line Aluno t = new Aluno();

Quote:

---

Originally Posted by alphasil

Well, i'm lost

:
:

Error saying

found no arguments in line Aluno t = new Aluno();

---

The error message is telling you exactly what's wrong. The Aluno class doesn't have a constructor that takes no parameters.

What parameters does the constructor expect?

db

Hi

Thank's for your help

Class Aluno have a construtor.

Code:

---


/**
    * Construtor
    */
    public Aluno(String nome, int ID)
    {
        this.nome=nome;
        this.id=ID;   
    }

---

Is not correct?

Thanks

Right. But when do you actually call that constructor?

Hi,

Thanks again

Quote:

---

Originally Posted by KevinWorkman

Right. But when do you actually call that constructor?

---

Well, i must see who are the students in the list so i use:

Code:

---

public boolean addAluno(Aluno aluno)
    {
        boolean estado = false;     
        for(int i=0; i<alunos.size(); i++)
        {
            Aluno t = alunos.get(i);
            if(t.getID()==nAluno)
            {
                System.out.println(t);
                return false;
            }
        }
      alunos.add(aluno);
      return true;
    }

---

But with this code always add a new student, even if the number are the same, wich is wrong...

At line #7; what is 'nAluno'?

kind regards,

Jos

Quote:

---

Originally Posted by JosAH

At line #7; what is 'nAluno'?

kind regards,

Jos

---

Sorry, was a error but i have problems anyway, can't compile

Code:

---

public boolean addAluno(Aluno aluno)
    {
        boolean estado = false;     
        for(int i=0; i<alunos.size(); i++)
        {
            Aluno t = alunos.get(i);
            if(t.getID()==aluno)
            {
                System.out.println(t);
                return false;
            }
        }
      alunos.add(aluno);
      return true;
    }

---

I understand why but don't know how to resolve,

if(t.getID()==aluno) - Int and String, should i convert int to string to resolve?

Thanks

Nope; 't' is an Aluno and 'aluno' is an Aluno; you want to compare their IDs, so:

Code:

---

if (t.getID() == aluno.getID())
  ...

---

kind regards,

Jos

Quote:

---

Originally Posted by JosAH

Nope; 't' is an Aluno and 'aluno' is an Aluno; you want to compare their IDs, so:

Code:

---

if (t.getID() == aluno.getID())
  ...

---

kind regards,

Jos

---

Thanks it works now, the only problem now if the student list, give me strange character...

My method is this one

Code:

---

public void listaAlunos()
    {
        System.out.printf("\nPercorrendo o ArrayList (usando iterator)\n");
        Iterator<Aluno> iterator = alunos.iterator();
        while (iterator.hasNext())
        {
            System.out.println(iterator.next());
     
        }
    }

---

The print gives me

Percorrendo o ArrayList (usando iterator)
Aluno@11a9732

And if i go to the class Aluno and use the method getNome the return is correct...

any help please??

Thanks

And when are you actually calling that method?

Hi

In the end of the class.

Code:

---

import java.util.Iterator;

public class Turma
{
    private ArrayList<Aluno> alunos; // Lista de alunos
    private String aluno;
    private int nAluno;
   
    public Turma()
    {
        alunos = new ArrayList<Aluno>();
    }

    /**
    * @param  numAluno 
    * @return            Aluno      */
    public Aluno getAluno(int numAluno)
    {
      for(int i=0; i<alunos.size(); i++)
      {
          Aluno t= alunos.get(i);
          if(t.getID() == numAluno)
          {
              return t;
          }
        }
      return null;
    }
   
    /**
    * @param  aluno
    * @return  True
    */
 public boolean addAluno(Aluno aluno)
    {
        boolean estado = false;     
        for(int i=0; i<alunos.size(); i++)
        {
            Aluno t = alunos.get(i);
            if(t.getID()==aluno.getID())
            {
                System.out.println(t);
                return false;
            }
        }
      alunos.add(aluno);
      return true;
    }
   
    public void listaAlunos()
    {
        System.out.printf("\nPercorrendo o ArrayList (usando iterator)\n");
        Iterator<Aluno> iterator = alunos.iterator();
        while (iterator.hasNext())
        {
            System.out.println(iterator.next());
     
        }
    }
}

---

This last method is the one who gives that strange character

That's because you're simply passing an instance of Aluno into System.out.println(). What should it print out? What is the String representation of an Aluno instance?

My question was not where are you calling System.out.println(). My question was about the other method you mentioned in your post, with the correct return value.

Hi

It should print the number and the name of aluno(student)
Instance Aluno represent the object Aluno with atributes (name and number)

correct?

Quote:

---

Originally Posted by alphasil

Hi

It should print the number and the name of aluno(student)

---

Why? Where are you telling it to do that? When do you call the method that does that?

Quote:

---

Originally Posted by alphasil

Instance Aluno represent the object Aluno with atributes (name and number)

correct?

---

Sure, but how should that be printed out? Name and then number? Number and then name? How should the number be formatted? All of that is up to you as a programmer, and Java doesn't just know how to do it automatically. You have to tell Java specifically what to print out and when to print it out. Telling it to print out an Object just calls that Object's toString() function, which prints out the stuff you're seeing now.

Quote:

---

Originally Posted by KevinWorkman

Why? Where are you telling it to do that? When do you call the method that does that?
Sure, but how should that be printed out? Name and then number? Number and then name? How should the number be formatted? All of that is up to you as a programmer, and Java doesn't just know how to do it automatically. You have to tell Java specifically what to print out and when to print it out. Telling it to print out an Object just calls that Object's toString() function, which prints out the stuff you're seeing now.

---

I have changed to:

Code:

---

public void listaAlunos()
    {
        System.out.printf("\nPercorrendo o ArrayList (usando iterator)\n");
        for( int i = 0; i < alunos.size(); i++ )
        {
                        System.out.println(aluno);
                }
    }

---

and now my print out is this

Percorrendo o ArrayList (usando iterator)
null
null
null
---------------------

So, my variable aluno is not printed...

I'm lost

Where do you set a value to variable 'aluno'? (hint: you don't do it anywhere in the code snippet you showed us).

kind regards,

Jos

Quote:

---

Originally Posted by JosAH

Where do you set a value to variable 'aluno'? (hint: you don't do it anywhere in the code snippet you showed us).

kind regards,

Jos

---

Hi,

thanks for your help and remarks

Well, like i said, i have 2 classes, one for register student and the other to a classroom, so after insert student, i must create an object in classroom class and add the student

Class classroom

Code:

---

import java.util.ArrayList;
import java.util.Iterator;
public class Turma
{
    private ArrayList<Aluno> alunos; // Lista de alunos
    private String aluno;
    private int nAluno;
   
    public Turma()
    {
        alunos = new ArrayList<Aluno>();
    }

 
    * @param  numAluno 
    * @return            Aluno
    */
    public Aluno getAluno(int numAluno)
    {
      for(int i=0; i<alunos.size(); i++)
      {
          Aluno t= alunos.get(i);
          if(t.getID() == numAluno)
          {
              return t;
          }
        }
      return null;
    }
    * @param  aluno
    * @return  True
    */
 public boolean addAluno(Aluno aluno)
    {
        boolean estado = false;     
        for(int i=0; i<alunos.size(); i++)
        {
            Aluno t = alunos.get(i);
            if(t.getID()==aluno.getID())
            {
                System.out.println(t);
                return false;
            }
        }
      alunos.add(aluno);
      return true;
    }
 
    public void listaAlunos()
    {
        System.out.printf("\nPercorrendo o ArrayList (usando iterator)\n");
        for( int i = 0; i < alunos.size(); i++ )
        {
                        System.out.println(aluno);
                }
    }
}

---

Class Aluno
[CODE=java]

public class Aluno
{
private int id; // Nº do aluno (identificador único)
private String nome; // Nome do aluno

/**
* Construtor
*/
public Aluno(String nome, int ID)
{
this.nome=nome;
this.id=ID;
}

public String getNome()
{
return nome;
}

public int getID()
{
return id;
}

public void SetNome( String name)
{
nome = name;
}
}
[CODE]

So, or i missing something...or i don't see what's wrong

Thanks

You really have to think about what you're doing here. What exactly are you printing out? What exactly is aluno? Hint: it's different from Aluno.

Break this up into smaller pieces. How do you get an instance from an array? Hint: you already did that in an earlier section of the code. How do you get a value contained by an instance? How do you print out a value?