Finding out if a list of Objects contains something with a specified field value?

Question

I have a list of DTO received from a DB, and they have an ID. I want to ensure that my list contains an object with a specified ID. Apparently creating an object with expect

Answer 1

Well, i think your approach is a bit overcomplicating the problem. You said:

I have a list of DTO received from a DB, and they have an ID.

Then probably you should use a DTO class to hold those items. If so put id getter and setter inside that class:

public class DTO implements HasId{
    void setId(Long id);
    Long getId();
}

That's enough for iterate through and ArrayList and search for the desired id. Extending ArrayList class only for adding the "compare-id" feautre seems overcomplicated o me. @Nikita Beloglazov make a good example. You can generalize it even more:

public boolean containsId(List list, long id) {
    for (HasId object : list) {
        if (object.getId() == id) {
            return true;
        }
    }
    return false;
}