Defensive Programming Practice

Defensive Programming

Defensive programming is a practice which is designed to ensure code correctness and reduce number of bugs and failures.

To follow Defensive Programming you need to have a kind of coding policy. In this article I will add my notes and vision of java defensive programming.


Don’t be paranoiac, by usage of a checking for null everywhere. Just use a rule “Never return a null” in your system and you will not have problems.


If a method is publicly available or receives a input from the outside world, enforce some defensive measures like IllegalArgumentException.

Put a known object first

It’s just never a bad idea to prevent a random NullPointerException by putting a known object on the left side of an equals().

if ("literal".equals(variable)) { ... }

if (variable.equals("literal")) { ... }

Always throw on switch default

So many time I saw then somebody has added a new enum item and didn’t modify switches which handle a logic by those enums.

switch (animal) {
    case CAT: foo(); break;
    case DOG: bar(); break;
        throw new ThreadDeath("That'll teach you");