for循环错误中访问Array.items []

Question

With the aim of getting a better performance I'm fine tuning the code, looking through the DDMS tracer. One aspect is Array.get(x) which is more expensive than Array.items[x]

We can directly access the items proving the array type is Object, or, we specify the array type in the constructor, like so:

Array<MyClass> foo = new Array<MyClass>(MyClass.class)

This works fine, however, how do I specify the last MyClass.class in a for loop? I have this at the moment:

for (Array<MyClass> listOfObjects : allObjects) {

    for (int i=0; i<listOfObjects.size; i++) {

        MyClass myObj = listOfObjects.get(i);   
        //MyClass myObj = listOfObjects.items[i];  

The commented line works fine, but trying to get rid of the overhead, I want to supply the `(MyClass.class)' like mentioned above. Where can I do this in that for-loop constructor?

Many thanks J

Answer 1

I think that what you're trying to do is pointless. Please read this great article: http://blog.codinghorror.com/the-sad-tragedy-of-micro-optimization-theater/

You are trying to generate some minimal optimization, while at the same time greatly reducing readibility and maintainability.

If you want less overhead, it would probably be wiser to look at a language like C++, rather than trying to hack basic java for loops.

Another thing you may want to look into is Java 8, which has added functionality for executing loops concurrently with Streams.

Answer 2

Array<MyClass> foo = new Array<MyClass>(MyClass.class)

Note that you are creating a NEW array with this line, passing it a class argument. From http://libgdx.badlogicgames.com/nightlies/docs/api/com/badlogic/gdx/utils/Array.html

Array(java.lang.Class arrayType)
Creates an ordered array with items of the specified type and a capacity of 16.

I don't see you trying to create new Arrays in the other code you posted. Are you trying to populate each listOfObjects in allObjects ? If so, you would want to do something like:

for (int i = 0; i < allObjects.size; i++)
{
    allObjects.items[i] = new Array<MyClass>(MyClass.class);
}

If you are simply trying to loop through these arrays, there is no class argument needed. I would suggest comparing the Array class to other Gdx or Java collections if the speed of iteration is too slow.

This quote from above link may also be notable if you do a lot of removing from the arrays.

A resizable, ordered or unordered array of objects. If unordered, this class avoids a memory copy when removing elements (the last element is moved to the removed element's position).