System.arraycopy VS toArray()

[Charith Fernando]

hi all,

i have a requirement where i get a set of id's and i have to search for the results and make an array out of the results...

  
public String[] getById(String[] ids){
String[] result = null;
/*
 * Search for ID's and then put the results
 * in another array and return.
 * 
 * the length of ids array and the length
 * of the result array may differ... 
 */
return result;
}

1) one way to do this is by adding the results into a List and then at the end convert the list into an array by using the toArray() method.

2) the other way is to define the array to be the size of the ids array and then add the results into it and remove the unused elements of the result array at the end by doing an arraycopy...

which method is more efficient?

[Jim Yingst]

This doesn't seem to have anything to do with SCJP, so let's move it to Java in General (Intermediate)...
[ October 28, 2006: Message edited by: Jim Yingst ]

[Jim Yingst]

Seems like the two techniques are pretty close. The first seems a little more natural to me, probably takes a little less code. Having to "remove" the unused array slots in the second technique seems like you're giving yourself an extra opportunity to make a silly coding mistake along the way - why bother, when ArrayList already takes care of such details?

[Charith Fernando]

so does that mean in performance wise both are same? as in you dont have a performance hit in either way?

would like to propose to open up a seperate section for performance tuning discussions... because we have to promote the most efficient way to do certain processes..
Thank you,

[Charith Fernando]

sorry... i think there's one thread available for that under the name "Performance"

[Ilja Preuss]

Hi Charith,

the very first rule to learn about performance optimization is that you should only optimize code that you have identified to be a performance bottleneck. Everything else will just take away time from caring about the important aspects of development.