Java Search an arraylist of strings for words that are in another arraylist

Question

As the title says, I have an arraylist of over 10000 words and I wish to use another arraylist of words where I chose the words to search for. Cant explain it more simple than that but there's the code you may catch on to what I am trying to achieve. Basically, one arraylist of a lot of words then another arraylist of 5 or so words that will check if those words appear in the long arraylist of words.

//TO DO: Profile the search method
 try {
 Scanner input = new Scanner(new File("textFile.txt"));
 int reps = 100;
 List<String> list = new ArrayList();
 List<String> searchValues = new ArrayList();
 searchValues.add("You");
 searchValues.add("and");
 searchValues.add("So");
 searchValues.add("we");
 searchValues.add("important");
 while (input.hasNext()) {
 list.add(input.next());
 }
 input.close();
 System.out.println("Amount of words in a .txt file: " + list.size());
 //Start to time the method
 long start = System.currentTimeMillis();
 for (int i = 0; i < reps; i++) {
 for (int j = 0; j < list.size(); j++) {
 //List value = index.search(list.get(j));
 List value = index.search(list.get(j));
 }
 }
 long end = System.currentTimeMillis();
 System.out.println("Time Taken: " + (end - start) + "ms");
 } catch (IOException exc) {
 System.out.println("File does not exist");
 exc.printStackTrace();
 System.exit(1);
 }

• Aleksandar Zoric: Will take a look now. Thank you.

Answer 1

list.retainAll(searchValues)

will remove all of the values from list which are not in searchValues. (Javadoc)

Answer 2

retainAll internally calls contains() which will iterate over the second list, so you get O(n x m) time complexity searching.

You could search for words by using a hashmap, inserting all entries and finding the ones which occured more than once. This should give you 2 x O(n) + O(m).

However, that would likely not matter if your second list only has 5 objects.

Answer 3

You can also use :

list.stream().filter(s -> ! searchValues.contains(s));

This will return a stream consisting of the elements that don't exist in the searchValues list (considering that you are working with Java 8).