Iterator in HashMap

[Mansi Vyas]

What is the equivalent of iterator in HashMap? How do I loop through the objects in the HashMap?
Mansi

[Jim Yingst]

You have three views which are Collections you can iterate through: keySet(), values(), and entrySet(). Many people do somethign like this:

for (Iterator it = map.keySet().iterator(); it.hasNext(); ) {
    SomeClass key = (SomeClass) it.next();
    OtherClass value = (OtherClass) map.get(key);
    doSomethingWith(key, value);
}

However, this is a big waste of time, performaing a get() on every singe key, which includes a hashCode() calculation. Completely unnecessary. If you want to get both keys and values, do something like:

for (Iterator it = map.entrySet().iterator(); it.hasNext(); ) {
    Map.Entry entry = (Map.Entry) it.next();
    SomeClass key = (SomeClass) entry.getKey();
    OtherClass value = (OtherClass) entry.getValue();
    doSomethingWith(key, value);
}

If you really only need the keys, use keySet(); if you only need values, use values(); if you need both, use entrySet().

[Mansi Vyas]

Thanks.