Fixing null pointer exceptions in Java (with ArrayList)

Answer 1

Of course it crashes - you've set it to null.

Why on earth didn't you heed the perfectly good advice you received here?

http://stackoverflow.com/questions/4061075/java-null-pointer-exceptions-dont-understand-why

You're wasting everyone's time on a trivial question. I'm voting to close.

Try this - it's still heinous, but it runs:

    package javaPractical.week3;
import javax.swing.*;
import java.util.ArrayList;
import java.util.List;

public class MovieList1
{

    private static int NUM_OF_MOVIES = 10;

    private List<Movie> myFavouriteMovies;
    private int numberOfMovies = 0;
    private int index = 0;

    public MovieList1()
    {
        this.myFavouriteMovies = new ArrayList<Movie>();
        this.numberOfMovies = 0;
        this.index = 0;
    }

    public int getNumberOfMovies()
    {
        return this.myFavouriteMovies.size();
    }

    public boolean isEmpty()
    {
        return this.myFavouriteMovies.isEmpty();
    }

    public void add(Movie movie)
    {
        this.myFavouriteMovies.add(movie);
    }

    @Override
    public String toString()
    {
        return "MovieList1{" +
               "myFavouriteMovies=" + myFavouriteMovies +
               '}';
    }

    public static void main(String[] args)
    {
        MovieList1 movieList = new MovieList1();
        String titleADD;
        String movieURLADD;
        String yearADD;
        String genreADD;
        String actorADD;

        titleADD = JOptionPane.showInputDialog(null, "Enter title:");
        movieURLADD = JOptionPane.showInputDialog(null, "Enter URL:");
        yearADD = JOptionPane.showInputDialog(null, "Enter year:");
        genreADD = JOptionPane.showInputDialog(null, "Enter genre:");
        actorADD = JOptionPane.showInputDialog(null, "Enter actor:");

        Movie TempMovie = new Movie(titleADD, movieURLADD, yearADD, genreADD,
                                    actorADD);

        // crashes here
        movieList.add(TempMovie);
        System.out.println(movieList);

    }
}

class Movie
{
    private String title;
    private String url;
    private String year;
    private String genre;
    private String actor;

    Movie(String title, String url, String year, String genre, String actor)
    {
        this.title = title;
        this.url = url;
        this.year = year;
        this.genre = genre;
        this.actor = actor;
    }

    @Override
    public String toString()
    {
        return "Movie{" +
               "title='" + title + '\'' +
               ", url='" + url + '\'' +
               ", year='" + year + '\'' +
               ", genre='" + genre + '\'' +
               ", actor='" + actor + '\'' +
               '}';
    }
}

Answer 2

You have defined static attribute private static ArrayList<Movie> myFavouriteMovies = new ArrayList();

But in the constructor you are assigning the null. After that you are invoking calls like myFavouriteMovies.size() which causes NullPointerException

public MovieList1() {
    this.myFavouriteMovies = null;
    this.numberOfMovies = 0;
    this.index = 0;
}