JAVA: Preventing Duplicate Entries to an ArrayList

Question

I am trying to prevent duplicate entries from being added to an ArrayList as the list is being populated whilst reading through each line of a file. Each line of the file is

Answer 1

It sounds like what you really want is a Set>

Set> pairs = ...
try(BufferedReader br = ... ) {
    for(String line; (line = br.readLine()) != null;) 
        pairs.add(new HashSet(Arrays.asList(line.split(" ")));
}

This creates a collection of pairs without duplicates regardless of the order of the words.