Example URL : https://www.youtube.com/channel/UCAoMPWcQKA_9Af5YhWdrZgw
I need only UCAoMPWcQKA_9Af5YhWdrZgw (Channel ID)
This is the pattern you can use to capture the channel id and this will validate the url also
^(?:(http|https):\/\/[a-zA-Z-]*\.{0,1}[a-zA-Z-]{3,}\.[a-z]{2,})\/channel\/([a-zA-Z0-9_]{3,})$
I have no idea how to execute regex in android but sharing the regex url, you can check from here https://regex101.com/r/9sjMPp/1
Or a javascript code to perform
var str = "https://www.youtube.com/channel/UCAoMPWcQKA_9Af5YhWdrZgw";
var pattern = /^(?:(http|https):\/\/[a-zA-Z-]*\.{0,1}[a-zA-Z-]{3,}\.[a-z]{2,})\/channel\/([a-zA-Z0-9_]{3,})$/;
var matchs = str.match(pattern);
console.log(matchs[2]);
// output is UCAoMPWcQKA_9Af5YhWdrZgw
Hope you get the idea.