Thanks Hugo for the nice tutorial. In the last example, are you trying to saying this (luckily this time == works although not recommended)
public class App { public static void main(String[] args) { Integer a = 1; Integer b = 1; if (a == b) { System.out.println("Equal!"); } else { System.out.println("Different!"); } } } -min On 2/25/14 5:41 AM, "Hugo Trippaers" <h...@trippaers.nl> wrote: >Anti-pattern: >An anti-pattern (or antipattern) is a common response to a recurring >problem that is usually ineffective and risks being highly >counterproductive. The term, coined in 1995 by Andrew Koenig, was >inspired by a book, Design Patterns, in which the authors highlighted a >number of design patterns in software development that they considered to >be highly reliable and effective. >‹ source http://en.wikipedia.org/wiki/Anti-pattern > > >Here at Schuberg we spend quite some time going through bugs reports from >automated scanners, you have probably seen the mails coming by on the ML. >As part of our work we have encountered a number of problems that keep on >popping up in the code base. So here is my first attempt to clarify why a >certain pattern is wrong and hopefully help developers to avoid this. > >So first up is the equality operator, ==. This operator is commonly used >in many languages to compare if two items are equal. The trick with this >operator in java is to know exactly what you are comparing, because it >matters. > >Consider this piece of code: > >public class App >{ > public static void main(String[] args) > { > int a = 1; > int b = 1; > > if (a == b) { > System.out.println("Equal!"); > } else { > System.out.println("Different!"); > } > } >} > >The expected outcome is ³Equal!² and indeed it prints just that. Now >consider the following code: > >public class App >{ > public static void main(String[] args) > { > Integer a = new Integer(1); > Integer b = new Integer(1); > > if (a == b) { > System.out.println("Equal!"); > } else { > System.out.println("Different!"); > } > } >} > >The result of running this bit of code is ³Different!². With == you are >telling the java compiler to compare the two variables. The variable are >references to Objects, so it will do exactly what you tell it to do, >compare the two object references. As you give it two different objects, >the result willl be ³Different!². The correct way of comparing the >contents of two objects is to use the equals method. Consider the >following piece of code: > >public class App >{ > public static void main(String[] args) > { > Integer a = new Integer(1); > Integer b = new Integer(1); > > if (a.equals(b)) { > System.out.println("Equal!"); > } else { > System.out.println("Different!"); > } > } >} > > >This will again be ³Equals!². > >Why is this often a problem? There are a lot or reasons why these bugs >came to exist in CloudStack (or any other project). For example somebody >might cause this bug by changing the return type of a function from long >to Long. The first one is a primitive which can be compared with == and >the second one is an Object which might result in another comparison than >you intended. Findbugs will catch these types of comparisons and warn you >for them. See commit d1efdca50622a0b67ae1a286aad3297b1c748e9e for an >example. > > > >Oh and what does this print? > >public class App >{ > public static void main(String[] args) > { > Integer a = 1; > Integer b = 1; > > if (a.equals(b)) { > System.out.println("Equal!"); > } else { > System.out.println("Different!"); > } > } >} > > >Surprise!, it prints ³Equals!². This is a boxed integer and java keeps a >pool of these so internally the object is cached and both a and b get the >same objects assigned to them by the internal boxing logic. Just never >rely on this! It only works in specific cases and is implementation >specific per JVM vendor and JVM version. > >Cheers, > >Hugo > > >P.S. If you have another anti pattern feel free to post em in this thread. >