[JAVA] Problem mit eigenen Objekten

public class Book {


	private String title;
	private String author;
	private String genre;
	private int year;
	private int isbn;
	public Book(String Title, String Author, String Genre, int Year, int Isbn)
	{
		title=Title;
		author=Author;
		genre=Genre;
		year=Year;
		isbn=Isbn;		
	}
	public String toString()
	{
		String output;
		output=title+", "+author+"\n"+year+"\n"+genre+"\n"+isbn;
		return output;
	}


}

public class Library {


	private int cap;
	private int capInc;
	private int realAmount=0;
	private Book [] books;

	public Library(int initialCapacity, int capacityIncrement)
	{
		this.cap=initialCapacity;
		this.capInc=capacityIncrement;
		for(int i=0;i!=cap;i++)
			books[i]=new Book("a","a","a",1,1);
		System.out.println(books.length);
	}
	public void insert(Book b)
	{
		if(realAmount<cap) //there is still some space left
		{
			//Search for free space
			for(int i=0;i!=cap;i++)
			{
				if(books[i]==null)
				{
					books[i]=b;
					realAmount++;
					return;
				}				
			}
			System.out.println("Error 0x001");
		}
		else if(capInc>0) //Try to increase space
		{
			cap+=capInc;
			if(realAmount<cap) //there is still some space left
			{
				//Search for free space
				for(int i=0;i!=cap;i++)
				{
					if(books[i]==null)
					{
						books[i]=b;
						realAmount++;
						return;
					}				
				}
				System.out.println("Error 0x002");
			}
		}
		System.out.println("Error 0x003: Couldnt increase size");
	}
	public void delete(Book b)
	{
		for(int i=0;i!=cap;i++)
		{
			if(books[i]==b)
			{
				books[i]=null;
				realAmount--;
				return;
			}
		}
		System.out.println("Error 0x002: Objekt nicht gefunden");
	}
	public void print()
	{
		for(int i=0;i!=cap;i++)
		{
			if(books[i]!=null)
			{
				books[i].toString();
			}
		}
	}

}