Why Map does not extend the Collection interface in Java Collections Framework?

Map interface is not compatible with the Collection interface.

Since Map requires key as well as value , for example, if we want to add key-value pair then we will use put(Object key, Object value). So there are two parameters required to add element to the HashMap object . In Collection interface add(Object o) has only one parameter.

Map supports valueSet , keySet as well as other appropriate methods which have just different views from the Collection interface.

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