Java™ How To Program (Early Objects), Tenth Edition

Preventing NullPointerExceptions

In Fig. 7.10, we created a deck array of 52 Card references—each element of every reference-type array created with new is default initialized to null. Reference-type variables which are fields of a class are also initialized to null by default. A NullPointerException occurs when you try to call a method on a null reference. In industrial-strength code, ensuring that references are not null before you use them to call methods prevents NullPointerExceptions.