根据其中一项将 ArrayList class 过滤到另一个

Question

I'm trying to sort my commentList and result with an itemList with only the items where the last value, itemPosition equals the current position. I have a class for the List items with 4 values:

class CommentItem {
    int profile; 
    String user;
    String message; 
    int itemPosition;
}

I am trying to use this code to sort it, but it is only adding the correct number of values instead of the actual values that I want.

for (CommentItem item : commentList) {
    if (item.getItemPosition() == position) {
        itemList.add(new CommentItem(
            commentList.get(position).getProfile(),
            commentList.get(position).getUser(),
            commentList.get(position).getMessage(),
            commentList.get(position).getItemPosition()
        ));
    }
}

This is the commentList :

commentList = new ArrayList<>();
commentList.add(new CommentItem(R.drawable.circleicon, "User0", "Message0", 1));
commentList.add(new CommentItem(R.drawable.circleicon, "User1", "Message1", 2));
commentList.add(new CommentItem(R.drawable.circleicon, "User2", "Message2", 3));
commentList.add(new CommentItem(R.drawable.circleicon, "User3", "Message3", 4));
commentList.add(new CommentItem(R.drawable.circleicon, "User4", "Message4", 1));
commentList.add(new CommentItem(R.drawable.circleicon, "User5", "Message5", 2));
commentList.add(new CommentItem(R.drawable.circleicon, "User6", "Message6", 3));
commentList.add(new CommentItem(R.drawable.circleicon, "User7", "Message7", 4));
commentList.add(new CommentItem(R.drawable.circleicon, "User8", "Message8", 0));

The resulting itemList with the position has these items displayed:

commentList.add(new CommentItem(R.drawable.circleicon, "User0", "Message0", 1));
commentList.add(new CommentItem(R.drawable.circleicon, "User1", "Message1", 2));

I have also tried all of these codes:

for (CommentItem item : commentList) {
    if (item.getItemPosition() == position) {
        itemList.add(new CommentItem(
            item.getProfile(), item.getUser(), 
            item.getMessage(), item.getItemPosition()
    ));
    }
}

for (CommentItem item : commentList) {
    if (item.getItemPosition() == position) {
        itemList.add(item);
    }
}

for (CommentItem item : commentList) {
    if (item.getItemPosition() == position) {
        itemList.add(commentList.get(commentList.indexOf(item)));
    }
}

With the same result.

Thank you in advance!

Answer 1

First, declare your commentList correctly to avoid compile errors:

ArrayList<CommentItem>commentList = new ArrayList<CommentItem>();

Also, it is more efficient to write:

...new ArrayList<CommentItem>(Arrays.asList(/*insert contents here*/));

Instead of .add().add().add()...

Alternatively, you could use a for loop to create all those new CommentItems. Since you are making user1, user2, etc..., just write:

for (int i = 0, j = 1; i < 9 && j < 5; i++, j++){
    commentList.add(
    new CommentItem(
    R.drawable.circleicon, ("User" + i), ("Message" + i), j));
}

Finally, to your question:

ArrayList<CommentItem> resultItems = new ArrayList<CommentItem>();
for (int index = 0; index < commentList.size(); index++){
    CommentItem item = commentList.get(index);
    if (item == commentList.get(commentList.size()-1))//last index{
    resultItems.add(item);
    }
}

The most important part of that is commentList.get(commentList.size()-1)) , which is an easy way to get the last element in a list.