Checking that a field in a List of Objects has a certain value?

Question

I have a list of Person Objects:

List<Person> allPersons = new ArrayList<Person>();

The Person object has a field called Address .

I would like to check that at least one Person in the list has a certain address How can I do this?

I know that there is a .containsValue() method when using a HashMap, but is there anything similar for an ArrayList ?

Edit: please note that I am searching for a specific field value within each object, not the object itself?

Answer 1

You have to iterate over the List one way or another.

One convenient way to do it is with Java8 Streams :

boolean found = allPersons.stream().anyMatch(p->p.getAddress().equals(someAddress));

Answer 2

You can use asLazy() and collect() from Eclipse Collections :

If you can use the MutableList interface:

MutableList<Person> allPersons = Lists.mutable.empty();
boolean found =
    allPersons.asLazy().collect(Person::getAddress).contains(someAddress);

If you can't change the type of allPersons from List :

List<Person> allPersons = new ArrayList<>();
boolean found = 
    LazyIterate.collect(allPersons, Person::getAddress).contains(someAddress);

Note: I am a contributor to Eclipse Collections.

Answer 3

If you plan on making this check often, load the addresses in the Set<String> on which you can then call the contains method:

Set<String> allAddresses = 
   allPersons.stream().map(Person::getAddress).collect(toSet());
// ...
boolean found = allAddresses.contains(someAddress);

Answer 4

You could simply do while + iterator loop

boolean found = false;
Iterator it = allPersons.iterator();
Person currentPerson = null;

while(!found && it.hasNext()){
    currentPerson = it.next();
    if(currentPerson != null && paramAdress.equals(person.getAddress()){
        found = true;
    }
}

Answer 5

As a complement, if you don't feel comfortable with Eran's answer (which is the best possible answer) or you can't use Java 8, just create a method like:

public boolean checkAdress(String adress)
{
    boolean found = false;
    for(int i = 0; i < allPersons.size() && !found; i++)
        found = allPersons.get(i).getAdress().equals(adress);
    return found;
}

This is what I used to do before Java 8.