Count number of books in Arraylist

[Iwan van den Hoek]

Hi, I am new to Java programming and studying it at school.
We have been given an assignment to create a small library, with the following classes Library, Book, Author and Copy. With a given class Biblio which has predefined code and adds the books to the class book in an arraylist in Class Copy.
The UML Domain is attached so you know the flow of the classes
Everything is working fine and the generated output is correct.

There is just one method in class Library that is not working, the int method has to count the number of Copy's based on the Class Book (String):
I have to go through the Arraylist in Class Copy and look for a specific book and return the number of copy's.
Sorry for the Dutch language in the code.
I have tried multiple steps using a for loop
Now I have found a similar post the uses hashset, I have tried below code but the return comes back with 0. (There are 3 copy's)

package domein;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

import domein.Boek;
import domein.Exemplaar;

/**
 * 
 * Klasse die verantwoordelijk is voor het beheer van boeken
 * 
 */
public class Bibliotheek {
  private ArrayList<Exemplaar> boekenlijst = new ArrayList<Exemplaar>();
  

  /**
   * 
   * Print de naam van de Bibliiotheek.
   * 
   */
  public Bibliotheek(String string) {
    System.out.println(string);

  }

  /**
   * Methode om een alle exmeplaren van de opgegeven boek toe te voegen aan de
   * lijst.
   * 
   * @param b1
   * @param exemplaar
   */

  public void voegToe(Boek b1, int exemplaar) {
    for (int i = 0; i < exemplaar; i++) {
      Exemplaar e = new Exemplaar(b1, exemplaar);
      boekenlijst.add(e);

    }

  }

  /**
   * Methode om een boek toe te voegen aan de lijst.
   * 
   * @param b2
   */
  public void voegToe(Boek b2) {

    Exemplaar f = new Exemplaar(b2, 1);

    boekenlijst.add(f);
  }

  /**
   * Hiermee worden alle boeken van de bibliotheek opgevraagd en getoond op het
   * scherm.
   * 
   * @return
   */
  public ArrayList<String> toonCollectie() {
    ArrayList<String> titels = new ArrayList<String>();
    for (Exemplaar boek : boekenlijst) {

      System.out.println("Exemplaar --> " + boek.getTitel() + " "
          + boek.getAuteur() + " in taal " + boek.getTaal());
    }
    return titels;
  }

  /**
   * Hiermee worden alle Engelse boeken van de bibliotheek opgevraagd en worden
   * de exemeplaren in het Engels getoond op het scherm.
   * 
   * @param string
   * @return
   */
  public ArrayList<Exemplaar> toonCollectie(String string) {
    for (Exemplaar boek : boekenlijst) {
      if (boek.getTaal() == string)

        System.out.println("Exemplaar --> " + boek.getTitel() + " "
            + boek.getAuteur() + " in taal " + boek.getTaal());
    }
    return boekenlijst;

  }

  /**
   * Hiermee worden alle auteurs welke een prijs hebben opgevraagd in de
   * bibliotheek en degene met een prijs worden op het scherm getoond.
   * 
   * @return
   */
  public boolean printAuteurs() {
    for (Exemplaar auteur : boekenlijst)
      if (auteur.getPrijs(true))
        System.out.println(auteur.getAuteur());
    return false;

  }

  /**
   * Een methode om door de boekenlijst te gaan en de totaal aantal exemplaren
   * op te vragen.
   * 
   * @param b1
   * @return
   */

  public int telExemplaren(Boek b1) {
   Set<String> set = new HashSet<String>();
    int count = 0;
    for (Exemplaar element : boekenlijst) {
      String names = element.getTitel();
      set.add(names);
    }

    for (String a : set) {
      for (Exemplaar element : boekenlijst) {
        String names = element.getTitel();
        if (a.equals(names)) {
          count++;
        }
      }

      count = 0;
    }

    return count;

  }
}

Any help is much appreciated. I have added the complete code

[Stefan Evans]

Yeah, posting the code with (Double) Dutch doesn't make it too user friendly. Boek --> Book I can understand, but what is Exemplaar?
Also posting the whole class wasn't necessary.
Presumably this is the method you were wanting help with:

public int telExemplaren(Boek b1) {
   Set<String> set = new HashSet<String>();
    int count = 0;
    for (Exemplaar element : boekenlijst) {
      String names = element.getTitel();
      set.add(names);
    }
 
    for (String a : set) {
      for (Exemplaar element : boekenlijst) {
        String names = element.getTitel();
        if (a.equals(names)) {
          count++;
        }
      }
 
      count = 0;
    }
 
    return count;
 
  }

>the int method has to count the number of Copy's based on the Class Book (String):
>I have to go through the Arraylist in Class Copy and look for a specific book and return the number of copy's.

My observations:
You don't appear to be using the b1 parameter for anything in this method. What is it meant for?
You are building up a set of book titles. What purpose does this serve?
Can you explain how this code is meant to work? i.e. In English rather than computerese , what are the steps you are trying to accomplish?

[Iwan van den Hoek]

Hi Stefan,

Thank you for replying.
Yeah I should of changed the Dutch but here is a quick translation:
Boek = Book
Bibliotheek = Library
Exemplaar = Copy
Autheur = Author
Boekenlijst = ListofBooks

To answer your question:
Yes that is the code I need help with.
What I am trying to accomplish is to create a method that will return the number of copy's based on the String value Book b1

b1 is a parameter of a Book that is listed in the Arraylist boekenlijst.

The Hashset part of the code is what I have found on this site. The building up of a set of book titles van be removed, I used the code as I thought it was necessary for the code to work.

public int telExemplaren(Boek b1) {
       
    for (Exemplaar element: boekenlijst)
    {
        String names = element.getTitel();   
        set.add(names);   
    }   
     
    int count=0;   

    for (String a: set)
    {
        for (Exemplaar element: boekenlijst)
        {
            String names = element.getTitel();   
            if (a.equals(names))   
            {   
                count++;   
            }   
        }   
        System.out.println(a + " " + count);  
        count = 0;
    }   
    
      return count;
    
    
   

  }

I tested the code above and the output from System.out.println(a + " " + count); is:
Einstein 1
Onder professoren 1
Het laatste bevel 1
Nooit meer slapen 3
De buitenvrouw 2

but that is not exactly what I need.


The Class Biblio requests the following line : System.out.println("There are "+bieb.telExemplaren(b1)+" copies of "+b1.getTitel());
and should print:
There are 3 copies of Nooit meer slapen


The return statement should return the number of copies. but it prints There are 0 copies of Nooit meer slapen
.

[Liutauras Vilda]

Line 22.

count = 0; ?

[Mark King]

If you only need one title, why are you checking all of the titles?

[Liutauras Vilda]

Iwan van den Hoek wrote:
The return statement should return the number of copies. but it prints There are 0 copies of Nooit meer slapen

At line 22 you reset count to 0.
At line 25 you return count.

[Iwan van den Hoek]

Thank you all for taking the time, but I figured it out.
I was going about it all wrong and thanks to a tip I got I changed the code to:

public int telExemplaren(Boek b1) {
  int count = 0;
  for (Exemplaar element: boekenlijst) {
    if (b1.getTitel().equals(element.getTitel())) {
      count++;
    }
  }
  return count;
}

This does exactly what it needs to do.

The code I used does work except not as a getmethode and Setting the count =0; outside the loop resets the count back to 0 when it is going through the Arraylist and so it returns the correct number instead of increasing the number it returns.

[Liutauras Vilda]

Iwan van den Hoek wrote:Thank you all for taking the time, but I figured it out.
I was going about it all wrong and thanks to a tip I got I changed the code to:

We are more than happy that you figured it out yourself.

One more thing: use brackets in all for's and if's. There are some missing, which means you can loose marks in a coding-style part.

Best luck with your assignment.