what is the difference between below two statements in application.properties file in spring boot

what is the difference between below two statements in application.properties file in spring boot.

server.port =8080
and
server.port = ${PORT:8080}

please help with the explanation

>Solution :

1. server.port = ${PORT:8080} will check for an environment variable PORT and take its value , if not present defaults to 8080.
2. server.port =8080 will always be 8080