CODEWITHSUNDEEP
javaarraylistcontains
Ali Baran
Ali Baran

Reputation: 11

Check for duplicate entries in arraylist

Dog and Cat class inherited from the Animal class and if I want to add in ArrayList, I use the codes 

pets.add(new Dog(name))

How can I find out if a name is used more than once?

I'm looking for something like : pets.contain(...)

Upvotes: 0

Views: 113

Answers (4)

Adrian Shum
Adrian Shum

Reputation: 40066

Your question is ambiguous.

If you want to find from a list, names that are used more than once, you can do something like 

pets.stream()
     .collect(Collectors.groupingBy(Animall::getName(), Collectors.counting()))
     .entrySet().stream()
     .filter(e->e.getValue() > 1)
     .map(e->e.getKey())
     .collect(Collectors.toList()));

which will give you a List<String> containing names appeared more than once

If you just want to check if a name exists in pets before you add to it, I think you should use Map<String, Animal> instead of a List.

Upvotes: 0

Lechucico
Lechucico

Reputation: 2112

There isn't a way of doing this with a native function.

You could try the following:

int number = 0;
for (int i=0; i<pets.size(); i++){ 
    if pets.get(i).getname().equalsIgnoreCase("nameYouWant") number++;
}

Upvotes: 0

Joeri Hendrickx
Joeri Hendrickx

Reputation: 17445

There is actually a contains method on List. It uses the equals method to check for equality, so if your Dog or Cat classes implement equals in a way that the same name means equality, you can simply use contains.

If for some reason you don't want to do that (because you need equality to mean something else), you can just iterate over the list and find an entry with the same name. Or alternatively, use a stream, like so: pets.stream().filter(pet -> pet.getName().equals(newName)).findAny().isPresent()

Upvotes: 1

Tomasz Bawor
Tomasz Bawor

Reputation: 1657

If you are using Java8 you can use something like: 

pets.stream().map(animal -> animal.getName()).contains(name);

which will return boolean whether name is already in List.

Another way is using for loop: 

boolean isNamePresent = false;
for (Animal pet: pets) {
    if(pet.getname().equals(name)) {
        isNamePresent = true;
    }
}

Upvotes: 0

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