Software Project Seminar VII: Tools of the Craft. 23 march 2006 Jevgeni Kabanov

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1 Software Project Seminar VII: Tools of the Craft 23 march 2006 Jevgeni Kabanov

2 Administrative Info Send your troubles to not to Ivo directly Next time will be an additional ChangeLogic training session (seminar second half). What would you like to hear and is it even needed? Jevgeni Kabanov, Webmedia AS 2

3 Reading Materials The Pragmatic Programmer: From Journeyman to Master by Andrew Hunt and David Thomas, Addison- Wesley, Oct 1999 IBM DeveloperWorks: Java Theory and Practice series, other Javarelated articles Jevgeni Kabanov, Webmedia AS 3

4 Overview Programming languages Text Files in the 21 st century Language Facilities Execution Model Comments & Documentation IDEs Verification Approaches Code Generators & DSL Jevgeni Kabanov, Webmedia AS 4

5 Text Files in the 21 st century Most programming languages are text-based Learn to use one good text editor (emacs, vi, ) Keep Knowledge in Plain Text Learn a Text Manipulation Language (perl, awk, ) Use the Power of Command Shells (bash, ) Jevgeni Kabanov, Webmedia AS 5

6 Text Files in the 21 st century Format your language to look compositional Apply same formatting conventions everywhere Use automatic formatters sparingly Do not insert meaningless information Jevgeni Kabanov, Webmedia AS 6

7 Object-Oriented Programming Encapsulation Unless your object is a record all fields should be private Inheritance Inheritance is very fragile Use utility methods or object aggregation instead of inheritance where possible Use inheritance when you have an Is-A relation Jevgeni Kabanov, Webmedia AS 7

8 Object-Oriented Programming Polymorphism (aka Dynamic Dispatch) The main tool of OOP Use interfaces instead of classes where possible Overloading Method type is a part of method name Aggregation (aka Containment) A solution for multi-inheritance Jevgeni Kabanov, Webmedia AS 8

9 Object-Oriented Programming Inversion of Control Hollywood principle: Don t call us, we ll call you Used by many frameworks for reducing boilerplate code Spring is your friend Can also be used on a smaller scale in your own code to decrease boilerplate Jevgeni Kabanov, Webmedia AS 9

10 Exceptions The idea of exceptions is to handle them in one place instead of many Use checked exceptions sparingly (extend RuntimeException) Never silence down an exception Reduce boilerplate exception handling using IoC Never catch Error or Throwable Jevgeni Kabanov, Webmedia AS 10

11 Garbage Collection Allows us to forget about deallocation? Not really, otherwise Java would have no memory leaks (the dangling reference problem) What about performance? Most of the current garbage collectors are blazingly fast (generational copying, ) If you make a lot of objects make them immutable and use Flyweight pattern Jevgeni Kabanov, Webmedia AS 11

12 Generics Bounded Parametric Polymorphism introduced in Java SE 5.0 & C# 2.0 Mainly used in collections: List<Long> l = new ArrayList<Long> Syntax inspired by C++ templates, but the concept is Weaker than C++ by expressibility (C++ templates contain a Turing-complete sublanguage) Unlike them are typesafe Jevgeni Kabanov, Webmedia AS 12

13 Metadata (aka } class A { } Allows to add information to classes, fields and methods Useable at compile-time and run-time A perfect match with code generators A perfect match with AOP Used mainly to configure behaviour and dependencies (???) Jevgeni Kabanov, Webmedia AS 13

14 Reflectivity & Meta-programming Reflection allows to inspect object structure at run-time Dynamic proxies allow to emulate classes and interfaces at run-time Bytecode instrumentations allow to do both Java lacks a good typesafe metaprogramming facility Ruby is known for having one Jevgeni Kabanov, Webmedia AS 14

15 Aspect-Oriented Programming Aspects allow to capture crosscutting concerns and hold them in one place Examples: logging, transaction demarcation, undo/redo, exception handling, synchronization, Java main AOP implementation is AspectJ Spring supports a subset of AOP Jevgeni Kabanov, Webmedia AS 15

16 Execution Model Java is a compiled language Types are checked during compilation Errors come out early Code can be optimized within reasonable time-constraints Code is harder to decompile Compilation doesn t allow rapid turnaround Java can also be run within an interpreter (google DynamicJava) Jevgeni Kabanov, Webmedia AS 16

17 Execution Model Java bytecode is essentially an interpreted language JVM is very-very lazy Classes are loaded only on demand Method calls are resolved only at call time This late binding means that we can compile class A to one class B and run class A to a different class B with the same name Jevgeni Kabanov, Webmedia AS 17

18 ClassLoaders Java classloaders are Java objects responsible for loading the class definitions into JVM space Once loaded class cannot be unloaded Classloaders create a hierarchy with boot classloader being the root If a parent and a child classloader have a class in classpath, the parent will load it Class can see other classes only if they are visible from its classloader (or its parent) Jevgeni Kabanov, Webmedia AS 18

19 Comments & Documentation Write documentation for your reader Redundancy is sometimes necessary JavaDoc requires a lot of meaningless information Argument descriptions are most usually obvious from argument names and method javadoc Checked exceptions are most often thrown, since the called methods throw them Jevgeni Kabanov, Webmedia AS 19

20 IDE & Tools One IDE to rule them all (I m an Eclipse evangelist) NetBeans & IDEA also look good Modern IDEs include a compiler, a debugger and a profiler the whole language tool stack Plugins are the way to go Eclipse has the largest plugin community Jevgeni Kabanov, Webmedia AS 20

21 IDE & Tools Debugger Debugger is your greatest friend Inspect program state Put conditional breakpoints Note that in some cases debugger can modify the program state Trust Thy Libraries Profiler When in doubt profile! First write program to work, then profile it to work fast Jevgeni Kabanov, Webmedia AS 21

22 IDE & Tools Auto-completion & Auto-importing Greatly decrease the meaningless information one has to remember Make some entities harder to find than other Pick good names Put similar entities in similar places with similar names Semantical syntax highliting Jevgeni Kabanov, Webmedia AS 22

23 IDE & Tools Constant compilation (e.g. on save) Early error detection Allows to achieve rapid turnaround in Java Static analysis Eclipse compiler verifies and reports a lot of possible error situations Examples: boolean assignment, null dereferencing, Jevgeni Kabanov, Webmedia AS 23

24 Verification Contracts Use assert to check invariants inside your code Other contracts are usually documented, but can also be checked by tools like icontract Continuous integration It is important that every new revision of source code would be (automatically) compiled, run and tested Jevgeni Kabanov, Webmedia AS 24

25 Unit tests Java de-facto standard JUnit Provides assertions for different situations: asserttrue assertequals assertblah Tests are just methods with names testblahblah() Tests are gathered into test cases that extend junit.framework.testcase Test cases are gathered into test suites that extend junit.framework.testsuite Jevgeni Kabanov, Webmedia AS 25

26 Unit tests Test main cases Test border cases Test concurrency (if applicable) Use random data (if possible) Use tests to prove that you program is wrong, not that it is right!!! Remember no automated testing replaces the stupidity of a human Jevgeni Kabanov, Webmedia AS 26

27 Code Generators Use very simple custom code generators for annoyingly repeating encapsulated code Be vary of general code generators, unless they solve a very specific task or problem Good example: XDoclet Bad examples: macros, preprocessing Jevgeni Kabanov, Webmedia AS 27

28 Model Driven Architecture (MDA) Use a higher-level modelling language to simplify development UML & MOF as modelling language Isn t it easier to just embed the higher-level abstractions into our language? Very few practical examples exist The modelling language is fairly complex to understand Jevgeni Kabanov, Webmedia AS 28

29 Domain Specific Languages (DSL) Languages that are very suitable for their domain XPath, SQL can be viewed as DSL More interesting is a custom application language describing domain programming Very hard to design a language Rule-expert systems are a more suitable solution Jevgeni Kabanov, Webmedia AS 29

30 Discussion Jevgeni Kabanov, Webmedia AS 30