Collection entity initialization

mikehao · **Joined:** Sat Mar 31, 2007 2:10 am **Posts:** 3

Below is a sample class with one-to-many relationship to Part. My question is when we declare parts attribute as a Set, do we have to initialize it in the declaration (as in line 3)? Why?

Thanks,
Mike

Code:

public class Product {
    private String serialNumber;
    private Set parts = new HashSet();
    public Set getParts() { return parts; }
    void setParts(Set parts) { this.parts = parts; }
    public String getSerialNumber() { return serialNumber; }
    void setSerialNumber(String sn) { serialNumber = sn; }
}

ethnarch · **Joined:** Tue Aug 01, 2006 9:24 pm **Posts:** 120

I am not sure whether you have to with hibernate. But it's a very good practice in java to do so. You always want to avoid returning nulls whenever possible. Actually, I would say never return a null and if you do, you better have a really good reason for it.

nordborg · **Posted:** Wed Mar 25, 2009 5:16 pm

Quote:

My question is when we declare parts attribute as a Set, do we have to initialize it in the declaration (as in line 3)?

No you don't have to. But you have to watch out for 'null' in code like:

Code:

product.getParts().add(part);

Personally, I prefer this:

Code:

public Set getParts() { 
  if (parts == null) parts = new HashSet();
  return parts; 
}

It avoids the creation of a new HashSet that is just replaced by Hibernate in a call to setParts() every time an existing object is loaded from the database. In practice I don't think it matters which method you use, but I would get crazy if I had to check for 'null' every time I wanted to use a collection.