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 in the format "node1 node2" (tab delimiter). A duplicate here could either be "node1 node2" or "node2 node1". Here is my code to try and perform this operation:

while((line = bufferedReader.readLine()) != null) {

     String delimiter = "\t";
     String[] tempnodelist;  
     tempnodelist = line.split(delimiter);

     for (int i=0; i <= edgesnumber; i++) {   //edgesnumber = edges.size()

         if (tempnodelist[0] && tempnodelist[1] != edges.get(i)) {

             edges.add(line);

            }
        }

     nodes.add(tempnodelist[0]);  
     nodes.add(tempnodelist[1]); //intial intended use of tempnodelist.

}

Since I'm already splitting each line to make a HashSet of each node, I'm trying to use this to check for duplicates. At the moment I just can't seem to get the syntax right. How can I check through previous entries of the ArrayList for duplicates, and prevent them from being added, whist continuing to populate the ArrayList? what is wrong with this code currently?

Please ask any questions if anything is unclear,

Thanks in advance!

Answer 1

Use a LinkedHashSet and then convert it to an ArrayList, because a LinkedHashSet has a predictable iteration order (the insertion-order) and it is a Set.

For example

LinkedHashSet<String> uniqueStrings = new LinkedHashSet<String>();

uniqueStrings.add("A");
uniqueStrings.add("B");
uniqueStrings.add("B");
uniqueStrings.add("C");
uniqueStrings.add("A");

List<String> asList = new ArrayList<String>(uniqueStrings);
System.out.println(asList);

will output

 [A, B, C]