Question about UART interrupt

hi to all,

UART is working as polling method, interrupt method and DMA method . My question is that how i come to know which method it is following ??
And if I want to change method how I can ?

And last one which one is default method ?

The method used is up to the application. The peripheral_server_UART example configures the UART interface for DMA mode. The DMA transfers any incoming data over the UART interface to memory without extra work by the processor saving power. Then every 20ms the application checks the status of the DMA buffer and if there is data in it the data is sent over the radio. Likewise any received data from the radio is stored in a memory buffer, then a DMA transfer is started to push that data out the UART interface.

Alternatively the application could have used an interrupt from the UART interface to know when a byte was received or there was room to transmit a byte, or lastly the application could periodically poll the UART fast enough to not miss newly arriving data and/or send data at the desired rate.