Don’t Repeat Yourself (DRY-Principle) ?
Table of contents
Why do you need source code conventions in your company?
An other common violation of the DRY principle is this one here :
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Source code convention tools
Literature, good books and references
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How to avoid the violation of the DRY-principle?
In this blog i'm gonna show you how to avoid violation of the DRY principle. The most important thing: i will tell you WHY you should not. I'm gonna give you some arguments, so that you are able to explain and motivate anybody at anytime.
What i hate, is the violation of the DRY principle by copy-pate or auto-comments. It seams to be a world wide "disease", because we all know it, but still continually violate this principle almost all the time. Let's figure out what i mean by doing a very trivial example:
Bad example 1 - DRY violation by repeating comments / making javaDoc obsolete:
/**
* The id
* @return id
*/
public long getId(){
return this.id;
}
This example is so trivial, the most of the programmers would say one of those sentences:
- it's ok, any programmer with a little experience is able to understand that.
- if a programmer does not understand that, then he is probabily on the false job
- it would be better without comments.
- it was auto-generated from eclipse.
- My checkstyle tool would fail if a did not comment it.
it sounds legtmin right? Well, if i was forced to do that, i would probabily say to my boss:
hey boss, i know you need me to do the work XYZ, but i have to rewrite (even better repeat) some pieces of my code to accomplish the rules we have in your company
What do you think, he would say? OK, i think you got it...let's jump this part and see how it should be and why!
Good example 1:
/**
* With this id you are able to retrieve the object from the
* database by calling {@link DAO#get(id)}
*
* @return id from the object to be retrieved
*/
public long getId(){
return this.id;
}
1 rule: we comment not what, but why we do something.
2. rule: we write an example how to use it, because in a year nobody knows that anymore
3. rule: writing a good comment, motivates and encourages junior programmers to do it correctly also.
4. rule: the javaDoc does not become obsolete this way and really helps
5. rule: a good comment can reduce maintenance efforts, when a bug is issued
6. rule: agility has nothing to do with zero documents! thats not the meaning. agility, means sustainability means, re-usability, understandable clean code and so on....
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An other common violation of the DRY principle is this one here :
Bad example 2 - DRY violation unconsciously:
/**comment ommited */
public void doThis(Object o){
if(o !=null){
// do something here...
}
}
/**comment ommited */
public void doThat(Object o){
if(o !=null){
// do something here...
}
}
this is an also very trivial example, but a really good one. such constructs are very often. instead of doing this way, do better this way here:
Good example 2:
/**comment ommited */
public void doThis(Object o){
doNotAllowNull ( o ) ;
// do something here...
}
/**comment ommited */
public void doThat(Object o){
doNotAllowNull ( o ) ;
// do something here...
}
/**comment ommited */
private <T> void doNotAllowNull(T anyObjectOfYourChoice){
final String msg = "YourExceptionHelpMessage";
if( anyObjectOfYourChoice == null){
throw new NullPointerException(msg);
}
}
Or this way here:
/**comment ommited */
private <T> boolean isNotNull(T anyObjectOfYourChoice){
return ( anyObjectOfYourChoice != null ) ? true : false ;
}
Even better:
Even better it would be to define an interface and a class that does that for you so that you don't have to write or implement it always from the scratch. you just have to delegate it to this class.
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Please rat it by clicking the google+1 or leaving some constructive comments or some bad examples from your companies and how you solve them. i also wanna learn from you. The next lesson will be: The KISS Principle. Stay connected and follow me. Do not miss it.
