Find the duplicate elements in arraylist and display [closed]

Answer 1

Map frequency = new HashMap();
for (String element : list) {
    if (frequency.contains(element)) {
        frequency.put(element, frequency.get(element) + 1);
    }
    else {
        frequency.put(element, 1);
    }
}
for (Map.Entry entry : frequency.entrySet()) {
    System.out.print(entry.getKey() + " = " + entry.getValue() + " ");
}
System.out.println();