Java collection not have Map as part of collection framework

Question

If your look at collection framework you will see the following, but Map is not in the list of interfaces. While we talk about map we say it is a part of collection framework, so if Map is a part of collection framework then why it is not in the interfaces list.

 java.util
Interface Collection

All Known Subinterfaces:
    BeanContext, BeanContextServices, List, Set, SortedSet

All Known Implementing Classes:
    AbstractCollection, AbstractList, AbstractSet, ArrayList, BeanContextServicesSupport, BeanContextSupport, HashSet, LinkedHashSet, LinkedList, TreeSet, Vector

Similar post: http://stackoverflow.com/questions/5700135/why-does-map-not-extend-collection-interface — Lorand Bendig, Aug 24 '12 at 07:38

score 18 · Answer 1 · edited Aug 02 '17 at 01:42

18

"The collection framework" and Collection interface are not the same thing.

While you can regard a map as a collection of entries, Map doesn't support that directly - you can get a set of entries with the entrySet method.

But fundamentally you need to distinguish between "the collection framework" and the Collection interface.

edited Aug 02 '17 at 01:42

Darrell Teague

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answered Aug 24 '12 at 07:30

Jon Skeet

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score 12 · Accepted Answer · edited Aug 02 '17 at 06:57

12

Maps work with key/value pairs, while the other collections work with just values. Map maps keys to values. It allows its content to be viewed as a set of keys, a collection of values and a set of key-value mappings.

Check this following link. Answer by oracle. https://docs.oracle.com/javase/tutorial/collections/

edited Aug 02 '17 at 06:57

Darrell Teague

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answered Aug 24 '12 at 07:35

Kalai Selvan Ravi

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score 4 · Answer 3 · answered Aug 24 '12 at 07:30

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Because Map is three collections: Keys, values and key-value pairs.

It's not easy to decide which one should be the default to iterate over, so it implements the interface three times (keySet(), values() and entrySet())

answered Aug 24 '12 at 07:30

Aaron Digulla

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Razvan · Answer 4 · 2012-08-24T09:10:13.150

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It's part of the collection framework but it doesn't implement the java.util.Collection interface.

It's a different branch of the hierarchy. If you want, you can view it on the same level of the hierarchy as the Collection interface.

The Collection interface is implemented by (is the root of) List-like Collections while Map is implemented by(is the root of) the KEY-VALUE-like collections.

edited Aug 24 '12 at 09:10

answered Aug 24 '12 at 07:33

Razvan

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score 1 · Answer 5 · answered Aug 24 '12 at 07:30

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The Map interface is not an extension of the Collection interface. However, it is a structure for keeping collections of data.

answered Aug 24 '12 at 07:30

Dan D.

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Java collection not have Map as part of collection framework

5 Answers5