WARNING 4! NPE when accessing index value of null array/collection Consider the following code written by a client of ChainSaw: ChainSaw myChainSaw = ChainSaw.initChainSaw(“QWE-T800”);ChainSaw[] friendsChainSaw = new ChainSaw[]{ ChainSaw.initChainSaw(“Q22-T450”), ChainSaw.initChainSaw(“QRT-T300”), ChainSaw.initChainSaw(“Q-T900”), null, // ops! ChainSaw.initChainSaw(“QMM-T850”), // model is not supported ChainSaw.initChainSaw(“ASR-T900”)};int score = myChainSaw.performance(friendsChainSaw); Creating an array of ChainSaw was quite challenging in this example. […]
Month: March 2024
Revealing a common mistake with Strings 2 – Objects, Immutability, Switch Expressions, and Pattern Matching
WARNING 1! NPE when calling an instance method via a null object Consider the following code written by a client of ChainSaw: ChainSaw cs = ChainSaw.initChainSaw(“QW-T650”); cs.start(); // ‘cs’ is null The client passes a chainsaw model that is not supported by this class, so the initChainSaw() method returns null. This is really bad because […]
Revealing a common mistake with Strings – Objects, Immutability, Switch Expressions, and Pattern Matching
46. Revealing a common mistake with Strings Everybody knows that String is an immutable class. In Java Coding Problems, First Edition, Chapter 2, Problem 48, we have even dissected how this class works and what are the consequences of its immutability.Even so, we are still prone to accidentally write code that ignores the fact that […]