Question

I have a class that holds another objects inside it (List, Set and objects from my application).

public class SomeClass {
    private List l;
    private SomeObject obj;
    //...
}

Is a good practice instantiate these objects where the SomeClass object is created to avoid NullPointerException? Something like:

public class SomeClass{
    private List l = new ArrayList();
    private SomeObject obj = new SomeObject();
    //...
}

In a normal way, these objects will be generated in some processing/analysis, but errors can occur and the objects still with null value.

Answer 1

Yes, it is a good practice to do so. The constructor is a natural place to instantiate member objects. You can also create them right where they are declared:

private List l = new ArrayList();

However, it might be a good idea to restructure or modify your code so that NullPointerExceptions won’t occur, regardless of the order in which the methods are called.