Java see if arraylist contains string

Question

I have a class called Paragens like this:

public class Paragens {
    static int contadorParagens = 1;

    String nomeParagem;
    int id;

    public Paragens(String nomeParagem) {
        this.nomeParagem = nomeParagem;
        this.id = contadorParagens++;
    }

    // getters and setters for nomeParagem
}

Every Paragens object has a name and an Id.

This class has a main method where I create several Paragens objects and store them inside an ArrayList like this:

public static void main(String[] args) {
    ArrayList<Paragens> paragens = new ArrayList<Paragens>();
    paragens.add(new Paragens("name1");
    // ... add more paragens
}

This is working ok. If I insert a bunch of paragens and print them I can see tat is all ok.

What I am trying to do is to ask the user to input a paragem name and then I want to see if that paragem is already in the ArrayList.

String name;
System.out.println("Insert paragem name: ");
pickName = sc.nextLine();
System.out.println(paragens.contains(pickName));

What am I doing wrong?

Answer 1

contains checks to see if the list contains the actual thing you handed it. In this case, you're passing in a String name, but comparing it to Paragem instances. contains can't magically guess that it's supposed to look at a given property on the Paragem instances to compare the string.

You can easily loop the list to find out for yourself:

boolean found = false;
for (Paragem p : paragems) {
    if (p.nomeParagem.equals(pickName)) { // Or use an accessor function for `nomeParagem` if appropriate
        found = true;
        break;
    }
}

...or as a function:

boolean containsParagemWithName(ArrayList<Paragem> paragems, String pickName) {
    for (Paragem p : paragems) {
        if (p.nomeParagem.equals(pickName)) {
            return true;
        }
    }
    return false;
}

Answer 2

Well, you need to implement the contains method yourself. Do a for loop over the entire array and check if the name of one of the elements is equal with what you're trying to add. If not, add a new Paragens(pickName) .

Answer 3

Objects by default are compared by their memory location . So if you have two Paragem with the same name, they are still not equal.

So either, you check the name of each one:

boolean checkDuplicate(String pickName) {
    for (Paragem p : paragems) {
      if (p.nomeParagem.equals(pickName)) return true;
    }
    return false;
}

or implement (override) the equals method to compare names (you should be calling contains on a new Paragem object then instead of a String , though).