Question: ```
array[obj][obj] = 1;

```

I want to create 2D array whose index is user defined object. How to do this? or there is some other data structure available to do this?

Answer: 
Android will use `res\values-v21\styles.xml` if the user's device is running Android API level 21+ (Android 5.0+) & will use `res\values\styles.xml` for older versions
It just means that the styles differ in android versions.

`styles.xml` in values-v21 mean that, that particular style is for Android API 21 version 5.0+

while `styles.xml` will be for any other Android version besides 5.0+.

its the same as language where you create an activity for en, fr, pk etc.

Older version would automatically be targetted by the `values/styles.xml` file.