无法从Java中的字符串数组获取匹配的字符串值

Question

I have string value which contain email addresses separated by comma and i have to check whether any same mail address been added from String array i have splitted using regex using comma and then not sure what i am missing to check whether any duplicates found in string array

I have used split to get array of email addresses separated by comma and then declared two for loop to check. inside inner for loop i have specified condition but it is just printing all the mail addresses. How can i get matched email addresses and unique ones

public class EmailDomains {

    public static void main(String[] args) {

        String st = "test1@gmail.com,"
                + "test2@gmail.com,"
                + "test@yahoo.com,"
                + "test@hotmail.com,"
                + "test@rediff.com,"
                + "test@rediff.com,"
                + "wer@gmailcom";
        st.trim();
        String[] total = st.split("\\,");
        //System.out.println(total.length);
        for(int i=0;i<total.length;i++) {
            for(int j=0;j<total.length;j++)
            {
                System.out.println(total[i]+" --- "+total[j]);
                if(total[i].trim().equals(total[j].trim()))
                {
                    /*
                     * System.out.println(total[i]); break;
                     */
                }
            }
            //System.out.println(total[i]);
        }

    }

}

Need to get matched and unmatched email addresses from the above string

Friends i have to store matched mails in one array and unique one in another so that i can proceed for validation with unique mail id's, please give me an idea as i am beginner i need help and thanks in advance

Answer 1

You are passing through the list two times – with i and again with j . Sometimes i and j are the same value, say "3". In that case if(total[i].trim().equals(total[j].trim())) is true - which makes sense because you're comparing a specific entry in the list to itself.

It looks like you want to ignore when i and j are the same. You can do this by adding an if check, something like this:

for (int i = 0; i < total.length; i++) {
    for (int j = 0; j < total.length; j++) {
        if (i != j) {
            if (total[i].trim().equals(total[j].trim())) {
                System.out.println(total[i] + " --- " + total[j]);
            }
        }
    }
}

Answer 2

to keep it a little more simple, i suggest to use a HashMap to collect email-addresses and counts

    final String st = "test1@gmail.com,"
                    + "test2@gmail.com,"
                    + "test@yahoo.com,"
                    + "test@hotmail.com,"
                    + "test@rediff.com,"
                    + "test@rediff.com,"
                    + "wer@gmailcom";
    st.trim();
    final String[] total = st.split(",");
    final Map<String, Integer> map = new HashMap<>();
    for (final String mail : total) {
        if (map.containsKey(mail)) {
            int count = map.get(mail).intValue();
            count++;
            map.put(mail, Integer.valueOf(count));
            continue;
        }
        map.put(mail, Integer.valueOf(1));
    }
    final Iterator<Entry<String, Integer>> iterator = map.entrySet().iterator();
    while (iterator.hasNext()) {
        final Entry<String, Integer> next = iterator.next();
        System.out.println(next.getKey() + " - " + next.getValue().toString() + " entries");
    }

Answer 3

You can do this in java8 with the streams api. To get two lists, one with unique addresses and one with duplicates, use a grouping collector. For example

    String st = "test1@gmail.com,"
            + "test2@gmail.com,"
            + "test@yahoo.com,"
            + "test@hotmail.com,"
            + "test@rediff.com,"
            + "test@rediff.com,"
            + "wer@gmailcom";
    st.trim();
    String[] total = st.split("\\,");
    List<String> unique = new ArrayList<>();
    List<String> duplicate = new ArrayList<>();
    Arrays.stream(total)
            .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()))
            .forEach((k, v) -> {
                if (v > 1) {
                    duplicate.add(k);
                } else {
                    unique.add(k);
                }
            });