修改哈希表中的值

Question

Hello I come to a problem with modifying certain value in hashtable when two keys are equal.

I define my hashtable,

Hashtable<String, Integer> hash = new Hashtable<String, Integer>();

and my program fills it with some data with .put() method.

note: first column represents hex values

08 86
AA 10
FF 330
2A 54
E1 60

I can check for string duplicates with if(hash.containsKey(string x)){} . If I want to insert another data in hashtable, but with the same string hash.put("AA", 77); I simply dont know how to add the value in hashtable with my new value together and have hashtable with no duplikate strings. That means to have my final hastable looking likewise

08 86
AA 87
FF 330
2A 54
E1 60

Any suggestions?

Answer 1

String yourKey = "AA";
int val = 77;
if (hashtable.containsKey(yourKey))
    val += hashtable.get(yourKey));
hashtable.put(yourKey, val);

This checks for duplicates and then if there is, add original value to the table

Answer 2

You can change your HashTable to a HashMap<String, Integer> ( http://docs.oracle.com/javase/7/docs/api/java/util/HashMap.html ) since the put of HashMap will not add a new key:

Associates the specified value with the specified key in this map. If the map previously contained a mapping for the key, the old value is replace

Answer 3

You could change your Hashtable to contain an Array or a List of Integers and provide your own put method:

Hashtable<String, List<Integer>> hash = new Hashtable<String, List<Integer>>();

public void put(String key, Integer i) {
  if (hash.containsKey(key)) {
    List l = hash.get(key);
    if (l == null) {
      l = new ArrayList<Integer>();
      hash.put(key, l);
    }
    if (!l.contains(i)) {
      l.add(i);
    }
  }
}