Iterating hashtable in java

Question

I have a hashtable in java and want to iterate over all the value in the table and delete a particular key,value pair while iterating. Is there some way i could do that

Answer 1

You need to use an explicit java.util.Iterator to iterate over the Map's entry set rather than being able to use the enhanced For-loop syntax available in Java 6. The following example iterates over a Map of Integer, String pairs, removing any entry whose Integer key is null or equals 0.

Map<Integer, String> map = ...

Iterator<Map.Entry<Integer, String>> it = map.entrySet().iterator();

while (it.hasNext()) {
  Map.Entry<Integer, String> entry = it.next();

  // Remove entry if key is null or equals 0.
  if (entry.getKey() == null || entry.getKey() == 0) {
    it.remove();
  }
}

Answer 2

You can use a temporary deletion list:

List<String> keyList = new ArrayList<String>;

for(Map.Entry<String,String> entry : hashTable){
  if(entry.getValue().equals("delete")) // replace with your own check
    keyList.add(entry.getKey());
}

for(String key : keyList){
  hashTable.remove(key);
}

You can find more information about Hashtable methods in the Java API

Answer 3

So you know the key, value pair that you want to delete in advance? It's just much clearer to do this, then:

 table.delete(key);
 for (K key: table.keys()) {
    // do whatever you need to do with the rest of the keys
 }