A [dialog](https://www.google.com/design/spec/components/pickers.html#pickers-date-pickers) date picker is used to select a single date. The selected day is indicated by a filled circle. The current day is indicated by a different color and type weight.
The DatePicker is a very easy component from the top level API but quite complex inside. It has state to keep the currently viewed date and the currently selected value.