Question

In the Avoid Creating Objects section of the page Designing for Performance in the Android Developer documentation I read some paragraphs for which I am not able to visualize a code representation:

An array of ints is a much better than an array of Integers, but this also generalizes to the fact that two parallel arrays of ints are also a lot more efficient than an array of (int,int) objects. The same goes for any combination of primitive types.

• How would these ‘parallel arrays of ints’ look like? Would it be something like instead of having a method with a signature such as getData():int[][] returning

     [a][b]
     [c][d]
     [e][f]
  

  … it would be better to have two methods, each returning one of the ‘columns’ of data? as in:
  getFirstDimensionData():int[]

     [a]
     [c]
     [e]
  

  and a second one getSecondDimensionData():int[]

     [b]
     [d]
     [f]
  

• What is an ‘array of (int,int) objects? … something like an array of objects of a-type-not-yet-defined that has two int member instances defining its state?

The immediate next paragraph:

If you need to implement a container that stores tuples of (Foo,Bar) objects, try to remember that two parallel Foo[] and Bar[] arrays are generally much better than a single array of custom (Foo,Bar) objects.

… makes me think that the author is making up some sort of notation. I guess my key question is: is the author of the page using this (somethingX, somethingY) notation to refer to an arbitrary class that ‘wraps’ the elements inside the parentheses?

Finally, is this a standard notation or just something the author of the page created by himself and omitted to explain?

Can anyone, please, shed some light? 🙂

Thanks in advance,

Y

Answer 1

What they’re saying is that

class foo {
    int a;
    int b;
}

foo[] bar;

Is slower than

int[] foo;

With foo[row*2] being a and foo[row*2+1] being b.

The notation (foo, bar) is trying to symbolize a class that contains foo and bar (like (a,b) in my above example).

I don’t believe it’s a standard notation, but it wouldn’t be the first time I’ve been proven wrong.