使用地图在数组列表中查找重复项 <String, Integer> 输入顺序

Question

Hi everyone I am trying to print all the duplicated elements, this works fine but the outputs are not in order (either from user input or from the text file). I want to print all elements with order (duplicates are not printed). How do I do that? The codes are from this Find the duplicate elements in arraylist and display Thanks @Cory Kendall for the codes.

**********updated question: the code now works perfect with LinkedHashMap. Now I want the outputs to be printed with number bullets (ie, 1. name1 = 2 ) incrementally. Thanks

List<String> strings = new ArrayList<String>();
// suppose datas are entered by user incrementally or from a text files.

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 1

If you want to remember insertion order in your Map, you need to use LinkedHashMap . In your case you have to replace

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

with

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

Answer 2

HashMap没有排序或排序，如果您关心insertion order ，请使用LinkedHashMap如果您关心natural order ，请使用TreeMap 。

Answer 3

public class FindDup {
    public static void main(String[] args) {
        String str[] = { "yogi", "ram", "ram", "yogi", "yogi", "yogi", "raju", "raju", "ram", "yogi", };
        Map<String, Integer> map = new HashMap<String, Integer>();
        for (String s : str) {
            if (map.containsKey(s)) {
                map.put(s, map.get(s) + 1);
            } else {
                map.put(s, 1);
            }
        }
        for (Entry<String, Integer> e : map.entrySet()) {
            System.out.println(e.getKey() + "---" + e.getValue());

        }
    }
}

Answer 4

A LinkedHashMap will retain order.

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

About LinkedHashMap :

Hash table and linked list implementation of the Map interface, with predictable iteration order. This implementation differs from HashMap in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is normally the order in which keys were inserted into the map (insertion-order).