for each inside a for each – Java

If I understand correctly, what you want to do, in pseudo-code is the following:

for (Tweet tweet : tweets) {
    if (!db.containsTweet(tweet.getId())) {
        db.insertTweet(tweet.getText(), tweet.getId());
    }
}

I assume your db class actually uses an sqlite database as a backend? What you could do is implement containsTweet directly and just query the database each time, but that seems less than perfect. The easiest solution if we go by your base code is to just keep a Set around that indexes the tweets. Since I can’t be sure what the equals() method of Tweet looks like, I’ll just store the identifiers in there. Then you get:

Set<Integer> tweetIds = new HashSet<Integer>(); // or long, whatever
for (Tweet tweet : tweets) {
    if (!tweetIds.contains(tweet.getId())) {
        db.insertTweet(tweet.getText(), tweet.getId());
        tweetIds.add(tweet.getId());
    }
}

It would probably be better to save a tiny bit of this work, by sorting the list of tweets to begin with and then just filtering out duplicate tweets. You could use:

// if tweets is a List
Collections.sort(tweets, new Comparator() {
    public int compare (Object t1, Object t2) {
        // might be the wrong way around
        return ((Tweet)t1).getId() - ((Tweet)t2).getId();
    }
}

Then process it

Integer oldId;
for (Tweet tweet : tweets) {
    if (oldId == null || oldId != tweet.getId()) {
        db.insertTweet(tweet.getText(), tweet.getId());
    }
    oldId = tweet.getId();
}

Yes, you could do this using a second for-loop, but you’ll run into performance problems much more quickly than with this approach (although what we’re doing here is trading time for memory performance, of course).