what's the static inner class Entry in HashTable used for?

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Static nested class in Java, why?

I'm reading sourcecode in JDK HashTable, and there is some code snippet like below:

/** Hashtable collision list. */

private static class Entry<K,V> implements Map.Entry<K,V> {
    int hash;
    K key;
    V value;
    Entry<K,V> next;
    ...
} //end of Entry<K,V>

I know the Entry here is a private inner class, but it's also a defined static class; my concern is, it isn't enough to just define it as private inner class? What's the main usage here to define it as a static class?

Any guide or reply is highly appreciated.

If you try iterating a `Map.entrySet`, you'll know. – adarshr May 24 '12 at 08:56 — adarshr, May 24 '12 at 08:56

score 3 · Answer 1 · answered May 24 '12 at 08:58

It is static so that its instances do not contain a reference to the containing instance of the outer class.

Map.Entry is used to iterate through the elements of the map. It is needless for it to have a reference to the containing map, as it needs no access to the private fields of the map. So declaring it non-static would just use up extra space and weaken encapsulation.

what's the static inner class Entry in HashTable used for?

1 Answers1