Exception thrown when calling constructor, java.lang.NullPointerException

Question

I am currently working on a project for school that requires me to make an album library, and am being thrown error code "java.lang.NullPointerException" when using this:

 public static void main(String[] args) {
    Scanner kb=new Scanner(System.in);
    AlbumCollection ac= new AlbumCollection();
    Playlist p= new Playlist();
    System.out.println("Welcome to bbco's music library!");
    displayMenu();
    Album a;
    Song s;
    int ch=getChoice();
    while(ch!=8){
        switch (ch) {
            case 1:
                a=createAlbum();
                ac.addAlbum(a);
                break;
            case 2:
                ac.displayAlbums();
                break;

To call upon this:

public void displayAlbums(){
    for(int i=0;i<numalbum;i++){
    albumobjects[i].displayAlbum();
    }
}

Any help would be greatly appreciated