It is an android.os.Handler and java.util.concurrent.Executor at the same time.

Handlecutor.java

import android.os.Handler;
import android.os.Looper;
import android.support.annotation.NonNull;

import java.util.concurrent.Executor;


public class Handlecutor extends Handler implements Executor {

    public Handlecutor(@NonNull Looper looper) {
        super(looper);
    }

    @Override
    public final void execute(@NonNull Runnable command) {
        post(command);
    }

}