I am trying to return an empty list

Question

I'm new to list, but I'm trying to return an empty list through a method, so that list can be used somewhere else. But I don't know how to do it.

public List<Something> login (String user, String key){
    if (success) {
        System.out.println("Welcome");
        return  (THIS IS WHERE I WANT TO RETURN AN EMPTY LIST);
    } 

    System.out.println("Incorrect Information");
        return null;
}

Can you not just create the `List` wherever you need it instead of returning an empty one here? — achAmháin, Mar 12 '19 at 19:42

Ruslan · Answer 1 · 2019-03-12T21:37:23.243

4

If you are going to use it somewhere else, you can return any implementation of List interface. The most used:

new ArrayList<>();

Also there are a few ways to return an immutable empty list (means that you can not modify it):

return Collections.emptyList();
return List.of();  // from java9

See difference between them List.of() or Collections.emptyList()

Also see more about List implementations

edited Mar 12 '19 at 21:37

answered Mar 12 '19 at 19:41

Ruslan

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Worth noting emptyList() and of() returns two different types of List (they're a bit different in the implementation). – LppEdd Mar 12 '19 at 21:00

score 3 · Answer 2 · answered Mar 12 '19 at 19:32

3

How about:

return new ArrayList<>();

answered Mar 12 '19 at 19:32

Andronicus

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could you explain please – JMM Mar 12 '19 at 19:35
3

Nothing to explain, really. We're instantiating an empty list and returning it. – Andronicus Mar 12 '19 at 19:40

Some random IT boy · Accepted Answer · 2019-03-12T20:08:06.787

2

java.util.List is an interface and therefore you cannot instantiate one.

You should instantiate one of it's implementation classes and return that object.

Like return new ArrayList<>();

edited Mar 12 '19 at 20:08

answered Mar 12 '19 at 19:41

Some random IT boy

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Yes but it looks like he tried to do `return new List();` and the IDE doesn't let him do that; causing some confusion :) – Some random IT boy Mar 12 '19 at 20:07

I am trying to return an empty list

3 Answers3