Problem with null pointer

[AlarV]

Hello everyone I'm new to java and this forum and I have a problem that I need to solve:

I've created a program with a class and a main, which is this:


CLASS BOOK:

public class Book {
    private String title;
    private String author;
    private int FirstEdition;
    public Book(){
    title="";
    author="";
    FirstEdition=0;
    };
    public void SetTitle(String a){
        this.title=a;
    }
    public void SetAuthor(String a){
        this.author=a;
    }      
    public void SetFirstEdition(int a){
        this.FirstEdition=a;
    }
    public String GetTitle(){
        return this.title;
    }
    public String GetAuthor(){
        return this.author;
    }
    public int GetFirstEdition(){
        return this.FirstEdition;
    }
    

};

MAIN:

public static void main(String[] args) {
        
        int i;
        Book [] a= new Book[2];        
        for(i=0;i<2;i++){
        a[i].SetTitle("1984");
        a[i].SetAuthor("Orwell");
        a[i].SetFirstEdition(1980);
        }
        for(i=0;i<2;i++){
            System.out.println("Book Title:"+a[i].GetTitle());
            System.out.println("\nAuthor Name:"+a[i].GetAuthor());
            System.out.println("\nFirst Edition:"+a[i].GetFirstEdition());
        }
        }

I get this message:
Exception in thread "main" java.lang.NullP ointerException
at Askhsh4.Askhsh4 .main(Askhsh4.j ava:21)
Java Result: 1


Thanks everyone in advance!

[JosAH]

You have created an array that contains two Book references. Each of them can refer to (read: point to) a Book but they don't do that now (they are both equal to null as a matter of fact). Before you can do anything with one of your books you have to create them:

for (int i= 0; i < book.length; i++)
   book[i]= new Book();

When that loop has finished both array elements each point to a book.

kind regards,

Jos

[AlarV]

Oh my god, thank you so much my friend, I have been trying to figure out this since yesterday! :D :D

[Jibran]

You only need one FOR loop there.