I've tried looking at posts on this issue but am still having some trouble with this error in my code. So in the fourth line, I create an instance variable called `SongDatabase` to access the `SongDatabase` class. But when I get down to the line, `SongDatabase.addNewSong();` under `case 1`, I get a java.lang.NullPointerException: null error.

Interface class:

```
public class Interface 
{
    Scanner console = new Scanner(System.in);
    private SongDatabase SongDatabase;

    public static void main(String[] args) {
        Interface intFace = new Interface();
        intFace.run();
    }

    private void run() {
        switch (userInput) {
        case 1: 
            SongDatabase.addNewSong();
            break;
        case 2:
            SongDatabase.removeSong();
            break;
        case 3:
            SongDatabase.sortSongs();
            break;
        default:
            System.out.println("Please enter a valid number.");
            break;

    }
}

```

SongDatabase class:

```
public class SongDatabase {
    Scanner console = new Scanner(System.in);  
    private Song song1, song2, song3, song4;

public void addNewSong() {        
        if (song1 == null) {
            song1 = getFromUser();
        }
        else if (song2 == null) {
            song2 = getFromUser();
        }    
        else if (song3 == null) {
            song3 = getFromUser();
        }
        else if (song4 == null) {
            song4 = getFromUser();
        }
        else {
        System.out.println("The database is currently full. Please delete a song before adding a new one.");
       }    
    }

```

I've stepped through the debugger and I know that the instance variable, SongDatabase = null, which is probably causing the error? I previously had a line 

```
SongDatabase SongDatabase = new SongDatabase();
SongDatabase.addNewSong();

```

instead, but I realised this was creating a new SongDatabase object everytime and wiping what I had stored in there so I had to change it. I'd really appreciate a solution because I have no clue, thanks!