Efficiently filter an ArrayList in Java/Android

Question

I'm developing an Android app (Android 1.6), but this is probably a more general Java question.

I have an ArrayList of about 10,000 objects

the objects contain 3 strings (firstName, middleName, lastName).

The user is presented with a "search box" on android where they can search for a particular "object" by typing in part of the name.

I have a class (which I call Filterer) that searches through the list of 10,000 for matching objects and then returns them as a "sublist".

The search is a little bit SLOW (especially on an Android handset) and I'm sure I'm not doing the search/filtering in the most efficient manner possible.

Does anyone have any suggestions on how to speed up my search? My code is below. One possibility to to search against a secondary "masterList" that already has every piece of information in lowercase and concatenated…but there may be additional ways to improve this search that would also help.

TIA!!

public void filterNames() {
  this.filteredList.clear();
  String sv = this.searchString.toString.trim().toLowerCase(); // search value
  for (int i = 0; i < this.masterList.size(); i++) {
    MyObject d = this.masterList.get(i);
    String fn = d.getFirstName().toString().toLowerCase();
    String mn = d.getMiddleName().toString().toLowerCase();
    String ln = d.getLastName().toString().toLowerCase();

    if (fn.indexOf(sv) >= 0 || 
        md.indexOf(sv) >= 0 || 
        ln.indexOf(sv) >= 0) {
      this.currentList.add(d);
    }
  }
}

Answer 1

may be too late answer but it's help for other in stuck same problem.

Java 8 (2014) solves this problem using streams and lambdas in one line of code:

Using Stream Api you can filter data without for loop and more feature's are available.

List<MyObject> mFilteredMyObjectList = mMyObjectList.stream()
    .filter(d -> d.getFirstName().toString().toLowerCase().indexOf(sv) >= 0 
    || d.getMiddleName().toString().toLowerCase().indexOf(sv) >= 0 
    || d.getLastName().toString().toLowerCase().indexOf(sv) >= 0).collect(Collectors.toList());

For more info see below link,

Link1 Link2

Answer 2

Yes, it's certainly painful to lower-case several objects for each loop iteration (plus a possibly redundant toString?), and also bad practice to call list.size() for every iteration — that value should be cached before the loop starts.

Anyway, if you're working with this much data, is there a reason that you're not using an SQLite database for storage and displaying/filtering your list using CursorAdapter?

That would be the recommended way to implement something of this size.