Question

I am making a class that maps Strings to Integers. I want to be able to get the Integer associated with a particular String and iterate through the entries, which are defined as another class that implements Map.Entry<String, Integer>.

Currently I have this:

public class MyMap implements Iterable<MyEntry> {

private final Map<String, Integer> wrappedMap = 
    new HashMap<String, Integer>();

@Override
public Iterator<MyEntry> iterator() {
    return wrappedMap.entrySet().iterator();
}

    //more methods

}

It’s not compiling because of a type mismatch even though MyEntry implements Map.Entry<String, Integer>.

Is there a way to make a custom implementation of Map.Entry? Is there an easier way to do this that I’m overlooking? Thanks in advanced!

Answer 1

It’s not compiling because MyEntry is not a part of the hashmap at all. If you want to return a list of MyEntry then you need to copy the data elements into a MyEntry instance and load that into a collection. Which is going to be slow and consume a considerable amount of memory.

It should be:

@Override
public Iterator<Map.Entry<String,Integer>> iterator() {
    return wrappedMap.entrySet().iterator();
}

The call to entrySet() returns a Set which contains the mappings in the hashmap. So the iterator needs to iterate over Entry objects