Merging two array of classes

Question

I have this function that should merge two array of classes when id of array1 is equal to id of array2.

For simplicity I converted one array into an ArrayList so I can remove the occurrence merged into the other one..

I'm looking a way to improve it, also in cpu-time, because the two arrays can have more then 20000rows. The actual way, should take some time..

public Asset[] merge(Asset[] a2, ArrayList<countR> a)
{
 while (a.size()!=0){
 int i=0;
 Boolean b=false;
 while (i<a2.length && b==false)
 {
 if (a.get(0).id.equals(a2[i].id)){
 a2[i].TotaleRegistrazioni = a.get(0).tot; 
 b=true;
 } 
 i++;
 }
 a.remove(0);
 }
return a2;
}

• palacsint: Have you done any performance test which shows that this is a performance bottleneck? 20k item isn't so much...
• Marcx: without looking at the time to scroll the entire array, I only would like to know if there is a better way to do this :)

Answer 1

Staying with your original code you can change b to a simple break and you can change the inner while to a for which is easier to read:

public Asset[] merge2(final Asset[] firstArray, final ArrayList<CountR> secondList) {
 while (secondList.size() != 0) {
 for (int i = 0; i < firstArray.length; i++) {
 final CountR countR = secondList.get(0);
 final Asset asset = firstArray[i];
 if (countR.id.equals(asset.id)) {
 asset.TotaleRegistrazioni = countR.tot;
 break;
 }
 }
 secondList.remove(0);
 }
 return firstArray;
}

Searching in a HashMap should be faster than iterating through the whole array, so I'd do the following:

public Asset[] merge3(final Asset[] firstArray, final CountR[] secondArray) {
 final Map<Id, Asset> assetCache = new HashMap<Id, Asset>();
 for (final Asset asset : firstArray) {
 final Id id = asset.getId();
 assetCache.put(id, asset);
 }
 for (final CountR countR : secondArray) {
 final Id countRId = countR.getId();
 final Asset asset = assetCache.get(countRId);
 if (asset != null) {
 // I supposed that it's int
 final int total = countR.getTot();
 asset.setTotaleRegistrazioni(total); 
 }
 }
 return firstArray;
}

(I supposed that the Asset.id is unique in the array.) In this case you don't have to convert the second parameter to an array (just the first to a map). Maybe it worth playing with the initialCapacity and loadFactor parameters of the HashMap to avoid the resizing.