Map.Entry interface in java

Question

java.util.Map.Entry as I know is a public static interface in java.util package that returns collection view of a map but as far now I am confused with the static interface and as it is Map.Entry is it an inner interface if so how do we have inner static interfaces in java

Answer 1

The definition of Entry happens to live inside the definition of Map (allowed by java). Being static means you don't need an instance of Map to refer to an Entry.

It's easiest to show how to use Map.Entry by an example. Here's how you can iterate over a map

Map<Integer, String> map = new HashMap<Integer, String>();

for (Map.Entry<Integer, String> entry : map.entrySet()) {
    Integer key = entry.getKey();
    String value = entry.getValue();
    // do something with key and/or value etc
    // you may also alter the entry's value inside this loop via entry.setValue()
}

Answer 2

There isn't really anything to be confused about.

Yes, Java allows interfaces to be members of classes or other interfaces.

No, that does not mean anything special. It changes absolutely nothing about how you can use such an interface or what you can do with it.

It only changes the name of that interface and creates a strong conceptual link between it and its enclosing type. In this case, a Map.Entry represents an entry of a Map. The designers of the API apparently felt that it made sense to stress this connection by making it a member type.