Find the duplicate elements in arraylist and display [closed]

Answer 1

Use a HashMap

Map<String, Integer> freqMap = new HashMap<String, Integer>();

Answer 2

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

Answer 3

Use a HashMap. Here is a simple implementation

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

Map<String, Integer> counts = new HashMap<String, Integer>();

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

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

Answer 4

Create a Map<String, Integer>, and then iterate over your ArrayList.

Then for each element: -

• If it is already present in the Map, increment the Integer value for that element by 1
• If it is not present, add that element with an initial Integer value of 1

Answer 5

Use Google Guava library's MultiSet. It supports adding multiples of elements, and counting how many occurrences of each element the multiset contains.

Multiset<String> wordsMultiset = HashMultiset.create();
wordsMultiset.addAll(words);
for(Multiset.Entry<String> entry : wordsMultiset.entrySet() ){
     System.out.println("Word : "+entry.getElement()+" count -> "+entry.getCount());
}

Answer 6

use hashmap
like this:

Map<String, Integer> occurrencies = new HashMap<String, Integer>();
for (String word : list) {
    occurrencies.put(word, occurrencies.containsKey(word)
    ? occurrencies.get(word) + 1 : 1);
}
for (Entry<String, Integer> entry : occurrencies.entrySet()) {
    System.out.println("Word: "+entry.getKey()
                     + ", occurences: "+entry.getValue());
}