Reflection vs Switch and case in getting fields

Question

So is this faster:

for (int i = 0; i < example.length; i++) {
    switch (i) {
        case 0: return example.field0;
        case 1: return example.field1;
        case 2: return example.field2;
        case 3: return example.field3;
        case 4: return example.field4;
        case 5: return example.field5;
        case 6: return example.field6;
        case 7: return example.field7;
        case 8: return example.field8;
        case 9: return example.field9;
        case 10: return example.field10;
    }
}

Or this:

for (int i = 0; i < example.length; i++) {
    return example.class.getField("field" + i);
}

I just want to know because it seems a bit tedious doing the first one and I do not want to repeat lots of lines of code that are basically doing the exact same thing.

Looks like you want to use neither as this looks to be a great case for use of a `Map` such as a `HashMap`. Also please understand that reflection is very expensive. — Hovercraft Full Of Eels, Jun 11 '17 at 22:59
Both cases (as posted) can be greatly simplified. They're equivalent to `return example.field0;` since when `i == 0` that is what you return (and both loops start with `i` equal to `0`). — Elliott Frisch, Jun 11 '17 at 23:20

sruetti · Answer 1 · 2017-06-28T18:25:41.500

What exactly is field0...field10? Depending on the relation between these fields, you might want to organize them in an appropriate data structure.

Do you have 11 fields of the same type and (besides their index) the same meaning, like the x-coordinates of the points of a line. Then an Array or a List might be the correct data structure.
Do these 11 fields cover the same aspect of the object and could be considered to belong together but can be named individually, like e.g. metadata of a document. The you might use a map (as "Hovercraft Full Of Eels" suggests) or put them into their own object. If you put the fields into a map, you might want to use an enumeration as key.
Are these 11 fields basically independent of each other? Then please don't try to access them together but write a getter and setter per field.

"Tedious" and "many lines of code" is not a good guide. It may be a sign of a bad design that should be corrected (see above). Otherwise there's usually a workaround in your favorite IDE. Creating setters and getters should only be a click away!

Please use reflection only if there's no other way. For examples see How could Reflection not lead to code smells?. Reflection in Java has quite a few drawbacks: bad performance, complex and difficult to get right. The main argument against reflection is IMHO that the compiler and IDEs are not made for reflection. You rename field<x> to metadata<x>? The refactoring will not change [...] getField("field" + i); and the compiler will not complain!

But to answer the actual question: Reflection is most likely a lot slower than direct Java code.

Reflection vs Switch and case in getting fields

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