Android: String null pointer exception when android error string == null is always false

Question

I am scanning the users phone and getting a list of all device music uri.

I then use those these Uris to find the music metadata for setting in a RecyclerView. I have found that some of the songs don't have the artist,album or image metadata in the song so when I return the the value to the RecyclerView I try to account for this by setting the name, artist ect to a default title.

I tried isEmpty(), == "" and == null:

For the == null Android gives the error that it will never be null.

This is my code:

public class DeviceMusicCollection {

    public static ArrayList<DeviceMusicMetadata> getDeviceMusic(Context context)

    {
        // Get the list of songs on the device
        ArrayList <DeviceMusic> deviceMusicArray = MainActivity.deviceMusicStaticArrayList;

        // variables for metadata
        String metadataTitle;
        String metadataArtist;
        String metadataAlbum;
        byte [] metadataImage;

        //Create a new array to retrieve the metadata info for the songs
        ArrayList<DeviceMusicMetadata> deviceMusicMetadata = new ArrayList<>();

        // Create a metatdata retriever to collect metadata
        MediaMetadataRetriever mediaMetadataRetriever = new MediaMetadataRetriever();

        if (deviceMusicArray != null){

                for (int i = 0; i < deviceMusicArray.size(); i++ ){

                // Create a Uri for each song from the music file address
                Uri uri = Uri.fromFile(new File(deviceMusicArray.get(i).getMusicFileAddress()));

                // Set the datadource for the metadata retriever
                mediaMetadataRetriever.setDataSource(context, uri);

                // Extract the title or default
                metadataTitle = mediaMetadataRetriever.extractMetadata(MediaMetadataRetriever.METADATA_KEY_TITLE);

                    if (metadataTitle.isEmpty() || metadataTitle == null){
                        metadataTitle = deviceMusicArray.get(i).getMusicFileTitle();
                    }

                // Extract the artist or default
                metadataArtist = mediaMetadataRetriever.extractMetadata(MediaMetadataRetriever.METADATA_KEY_ARTIST);

                    if (metadataArtist.isEmpty()){
                        metadataArtist = "Artist Unknown";
                    }

                // Extract the album or default
                metadataAlbum = mediaMetadataRetriever.extractMetadata(MediaMetadataRetriever.METADATA_KEY_ALBUM);

                    if (metadataAlbum.isEmpty()){
                        metadataAlbum = "Album Unknown";
                    }

                // Extract the image (default handled in adapter)
                metadataImage = mediaMetadataRetriever.getEmbeddedPicture();

                deviceMusicMetadata.add(new DeviceMusicMetadata(metadataTitle, metadataArtist, metadataAlbum, metadataImage));
            }
        }
        return deviceMusicMetadata;
    }
}

As far as I can see I will have the same problem when setting:

String metadataTitle;
String metadataArtist;
String metadataAlbum;

I also tried initialising them in the for loop. I am sure it is something silly but not sure what.

Thanks in advance for your help

Where exactly you are getting error? Can you post logcat as it helps quick identification of problem — Mohammed Atif, Oct 10 '16 at 08:51
Hi, I am getting the error on the if statments wher I set metadataTitle, metadataArtis, metadataAlbum; — Nicholas Muir, Oct 10 '16 at 08:52

score 2 · Accepted Answer · answered Oct 10 '16 at 08:54

2

You need to check if it's not null before anything else you check.

Withing an if statement the argument are checked one after another in the order you write them So you're if should be like

                    if (metadataTitle == null || metadataTitle.isEmpty())

answered Oct 10 '16 at 08:54

pantos27

629
4
13

Awesome, never new the order mattered. First time I have had this problem. That fixed. Thanks! – Nicholas Muir Oct 10 '16 at 08:57
1

this is a short circuit operator.... so basically in || if the first condition evaluates true, it won't check the second one. but if the first condtion is false, it will evaluate the second condition. In | both the conditions are evaluated regardless as it isnt a short circuit – Kushan Oct 10 '16 at 09:08

score 2 · Answer 2 · answered Oct 10 '16 at 08:54

2

I think the problem is on how you guard against null when trying to assign metadataTitle:

    // …

    if (metadataTitle.isEmpty() || metadataTitle == null) { // <-- HERE
        metadataTitle = deviceMusicArray.get(i).getMusicFileTitle();
    }

    // …

By doing it that way, the program will call metadataTitle.isEmpty() before making sure it's not null while it should be the other way around.

Try doing this instead:

    // …

    if (metadataTitle == null || metadataTitle.isEmpty()) { // <-- HERE
        metadataTitle = deviceMusicArray.get(i).getMusicFileTitle();
    }

    // …

answered Oct 10 '16 at 08:54

Hadi Satrio

428
2
8

Happy to help! Please accept an answer so it could help people who are having this exact problem in the future. :) – Hadi Satrio Oct 10 '16 at 09:01
1

Doesn't matter. Note I said "an answer" and not "my answer". ;) – Hadi Satrio Oct 10 '16 at 09:05

Android: String null pointer exception when android error string == null is always false

2 Answers2