在arraylist中查找重复元素并显示

Question

有谁能够帮我？我需要编写一个程序,其中我有10个元素arraylist,我需要找到它有多少重复值,并计算和显示值.

例如:说我有

list = {"stack", "overflow", "stack", 
        "yahoo", "google", "msn", 
        "MSN", "stack", "overflow", "user" }

结果应该是:

stack = 3
overflow = 2
google = 1
msn = 2
yahoo =1
user = 1

Answer 1

使用HashMap.这是一个简单的实现

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 2

使用Google Guava库MultiSet.它支持添加多个元素,并计算多集包含的每个元素的出现次数.

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 3

hashmap
像这样使用：

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());
}