How to pass Object ArrayList through interface?

Question

I've an interface defined as

public interface QueryCompleteListener {
    void onQueryCompleted(int token, ArrayList<Object1> songList);
}

I'm using this interface to return callback. In some callbacks I want to pass ArrayList<Object1> and in some cases I want to pass ArrayList<Object2> through the interface.

If I declare interface method as

void onQueryCompleted(int token, ArrayList<Object> songList)

to pass any type of Object, it gives an error saying found Object1 required Object when I call this method by passing ArrayList<Object1>

Sumit Singh · Accepted Answer · 2016-05-25 07:29:37Z

9

Use following:

<T> void onQueryCompleted(int token, List<T> songList);

See Generic Methods for more details.

answered May 25, 2016 at 7:29

Sumit Singh

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Andy Turner · Accepted Answer · 2016-05-25 07:41:13Z

1

Unless you actually need a type variable in the method body, you can simply use:

void onQueryCompleted(int token, List<?> songList);

edited May 25, 2016 at 7:41

answered May 25, 2016 at 7:34

Andy Turner

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Zeromus · Accepted Answer · 2016-05-25 07:52:26Z

0

Wildcard is the way to go but you probably want some form of control over what type of object you are using.

Just make the custom classes (Object1, Object2, ...) implements a custom interface (CustomSuperInterface) and declare the collection like this

void onQueryCompleted(int token, List<? extends CustomSuperInterface> songList);

answered May 25, 2016 at 7:52

Zeromus

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