You can use your own code. You don't need to use the looping structure, if you don't want to use the looping structure as you said above. Only you have to focus to remove space or trim the String of the list.
If you are using java8 you can simply trim the String using the single line of the code:
myList = myList.stream().map(String :: trim).collect(Collectors.toList());
The importance of the above line is, in the future, you can use a List or set as well. Now you can use your own code:
if(myList.contains("A")){
//true
}else{
// false
}