Iterator over HashMap in Java

Question

I tried to iterate over hashmap in Java, which should be a fairly easy thing to do. However, the following code gives me some problems:

HashMap hm = new HashMap(         


        

Answer 1

The cleanest way is to not (directly) use an iterator at all:

• type your map with generics
• use a foreach loop to iterate over the entries:

Like this:

Map hm = new HashMap();

hm.put(0, "zero");
hm.put(1, "one");

for (Map.Entry entry : hm.entrySet()) {
    // do something with the entry
    System.out.println(entry.getKey() + " - " + entry.getValue());
    // the getters are typed:
    Integer key = entry.getKey();
    String value = entry.getValue();
}

This is way more efficient than iterating over keys, because you avoid n calls to get(key).