java hashmap key iteration

Yes, you do this by getting the entrySet() of the map. For example:

Map<String, Object> map = new HashMap<String, Object>();

// ...

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

(Ofcourse, replace String and Object with the types that your particular Map has - the code above is just an example).

With for-each loop, use Map.keySet() for iterating keys, Map.values() for iterating values and Map.entrySet() for iterating key/value pairs.

Note that all these are direct views to the map that was used to acquire them so any modification you make to any of the three or the map itself will reflect to all the others too.

for (Map.Entry<T,U> e : map.entrySet())
{
    T key = e.getKey();
    U value = e.getValue();
    .
    .
    .
}

In addition, if you use a LinkedHashMap as the implementation, you'll iterate in the order the key/value pairs were inserted. If that's not important, use a HashMap.

public class abcd {
    public static void main(String[] args)
    {
       Map<Integer, String> testMap = new HashMap<Integer, String>();
        testMap.put(10, "a");
        testMap.put(20, "b");
        testMap.put(30, "c");
        testMap.put(40, "d");
        for (Entry<Integer, String> entry : testMap.entrySet()) {
            Integer key=entry.getKey();
            String value=entry.getValue();
        }
    }
}