Find the duplicate elements in arraylist and display [closed]

Answer 1

Use a HashMap. Here is a simple implementation

List strings = new ArrayList();
strings.put("stack", "overflow", "stack", "yahoo", "google", "msn", "MSN", "stack", "overflow", "user");

Map counts = new HashMap();

for (String str : strings) {
    if (counts.containsKey(str)) {
        counts.put(str, counts.get(str) + 1);
    } else {
        counts.put(str, 1);
    }
}

for (Map.Entry entry : counts.entrySet()) {
    System.out.println(entry.getKey() + " = " + entry.getValue());
}