check if there are any elements from one arraylist in another one and print the same elements

Question

I want to check if the list "wordlist" has some elements from the list "list". If it has , these elements should be printed. Just have some difficulties with syntax to compare 2 lists in java. Here is my code:

File files = new File("E:/test/dictionary.txt");
String[] words = file.split(" ");
List<String> wordlist = Arrays.asList(words);
try {
    Scanner scanner = new Scanner(files);
    List<String> list = new ArrayList<>();

    while (scanner.hasNextLine()) {
        list.add(scanner.nextLine());
    }

    scanner.close();
    for (String word : wordlist) {
        System.out.println(word);
    }
    for (String oleg : list) {
        System.out.println(oleg);
    }
} catch (FileNotFoundException e) {
    e.printStackTrace();
}

possible duplicate of [Efficient intersection of two List in Java?](http://stackoverflow.com/questions/2400838/efficient-intersection-of-two-liststring-in-java) — Gil, Jun 01 '15 at 00:08

score 1 · Accepted Answer · answered Jun 01 '15 at 02:01

Perhaps I am misreading your question because the solution seems pretty simple to me. All you need to do is run a for-loop and use the ArrayList contains(Object O) method or run a nested for-loop and use the String equals(String O) method. See below.

METHOD 1:

for(int a = 0; a < wordlist.size(); a++)
    if(wordlist.contains(list.get(a)))
        System.out.println(list.get(a));

METHOD 2:

for(int a = 0; a < wordlist.size(); a++)
    for(int b = 0; b < wordlist.size(); b++)
        if(wordlist.get(a).equals(list.get(b));
            System.out.println(list.get(b));

In the second example I keep wordlist.size() as the factor in both loops because both list and wordlist should be the same size, or at least I assume that.

Also, with references or variables that more than one word, Java convention dictates that good practice would be to capitalize the first letter of all subsequent words, that is, wordlist should be wordList.

Hope this helps.

@OlegNekhayenko No problem. Happy I could help you. – Ungeheuer Jun 02 '15 at 17:55 — Ungeheuer, Jun 02 '15 at 17:55

score 0 · Answer 2 · answered Jun 01 '15 at 00:11

If I understand your question, use Collection.retainAll(Collection) (per the linked Javadoc to retain only the elements in this collection that are contained in the specified collection) like

wordlist.retainAll(list);
System.out.println(wordlist);
// for (String word : wordlist) {                              
//     System.out.println(word);                                
// }
// for (String oleg : list) {
//     System.out.println(oleg);
// }

check if there are any elements from one arraylist in another one and print the same elements

2 Answers2