When to use wrapper class and primitive type

Others have mentioned that certain constructs such as Collections require objects and that objects have more overhead than their primitive counterparts (memory & boxing).

Another consideration is:

It can be handy to initialize Objects to null or send null parameters into a method/constructor to indicate state or function. This can't be done with primitives.

Many programmers initialize numbers to 0 (default) or -1 to signify this, but depending on the scenario, this may be incorrect or misleading.

This will also set the scene for a NullPointerException when something is being used incorrectly, which is much more programmer-friendly than some arbitrary bug down the line.

Generally, you should use primitive types unless you need an object for some reason (e.g. to put in a collection). Even then, consider a different approach that doesn't require a object if you want to maximize numeric performance. This is advised by the documentation, and this article demonstrates how auto-boxing can cause a large performance difference.

In my opinion, if my class members are wrapper variables, it does not rely on default values, which is developer friendly behavior.

1.

class Person {
   int SSN ; // gets initialized to zero by default 
}

2.

class PersonBetter {
  Integer SSN; //gets initialized to null by default
}

In the first case, you cannot keep SSN value uninitialized. It may hurt if you are not checking if the value was set before you attempt to use it.

In the second case, you can keep SSN initialized with null. Which can lead to NullPointerException but it is better than unknowingly inserting default values(zero) as SSN into to the database whenever you attempt to use it without initializing SSN field.