Map function in Java
Tuesday, August 31st, 2010I read on some email signature something along the lines of:
“If I had a dollar for every for(int i=0; i < size; i++) { ... } I've written I'd be rich"
After coding on Android and learning about some of the tips for performance, like
"With an ArrayList, a hand-written counted loop is about 3x faster"
If you do use ArrayLists a lot you then have that tip in the back of your head and you end up with a lot of code like the following:
List<T> myList = … ;
int size = myList.size();
for (int i=0; i < size; i++) {
T elem = myList.get(i);
//do something with elem
}
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Eventually there was a moment when I said, I need a freaking map function, I'm sick of this little pattern, surprisingly I couldn't find a map() function anywhere on the java collection framework. So I went and did this.
//what I think would be the equivalent of a lambda or closure in Python...
public interface MapFunction<T> {
public void map(T t);
}
And then on one of my utils classes I added a static method map that looks like this:
public static <T> void map(List<T> list, MapFunction<T> mapFunction) {
int size=list.size();
for (int i=0; i < size; i++) {
mapFunction.map(list.get(i));
}
}
So now, everytime I need to iterate over a whole list and do something to each element it's a lot cleaner
//let's serialize all the messages...
List<Message> messages = ...;
Utils.map(messages, new MapFunction<Message> {
public void map(Message message) {
Engine.INSTANCE.SERIALIZER.save(message);
}
});
done deal.
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