How to create Hexagon shape in .xml format

The best solution for you would be use VectorDrawable:

Hexagon shape as vector drawable:

<vector android:height="24dp" android:viewportHeight="628.0"
android:viewportWidth="726.0" android:width="27dp" xmlns:android="http://schemas.android.com/apk/res/android">
<path android:fillColor="#00ffffff"
    android:pathData="m723,314c-60,103.9 -120,207.8 -180,311.8 -120,0 -240,0 -360,0C123,521.8 63,417.9 3,314 63,210.1 123,106.2 183,2.2c120,0 240,0 360,0C603,106.2 663,210.1 723,314Z"
    android:strokeColor="#000000" android:strokeWidth="4"/>
</vector>

Update(28:07.2016):

To support API below Lollipop use support library http://android-developers.blogspot.com/2016/02/android-support-library-232.html remember to use VectorDrawableCompat instead VectorDrawable