Java Reference
In-Depth Information
public static void listEntries(Map<String,String> map) {
System.out.println("Entry Set:");
// Get the entry Set
Set<Map.Entry<String, String>>entries = map.entrySet();
entries.forEach((Map.Entry<String, String> entry) -> {
String key = entry.getKey();
String value = entry.getValue();
System.out.println("key=" + key + ", value=" + value);
});
}
}
Map: {Donna=(205)678-9823, Ken=(205)678-9823, John=(342)113-9878, Richard=(245)890-9045}
Key Set:
Donna
Ken
John
Richard
Values Collection:
(205)678-9823
(205)678-9823
(342)113-9878
(245)890-9045
Entry Set:
key=Donna, value=(205)678-9823
key=Ken, value=(205)678-9823
key=John, value=(342)113-9878
key=Richard, value=(245)890-9045
Sorted Maps
A sorted map stores entries in a map in an ordered way. It sorts the map entries on keys based on either natural sort
order or a custom sort order. The natural sort order is defined by the Comparable interface of the keys. If the keys do
not implement the Comparable interface, you must use a Comparator object to sort the entries. If the keys implement
the Comparable interface and you use a Comparator object, the Comparator object will be used to sort the keys.
An instance of the SortedMap interface represented a sorted map. The SortedMap interface inherits from the Map
interface. A SortedMap is to a Map what a SortedSet is to a Set .
The SortedMap interface contains methods that let you take advantage of the sorted keys in the map. It has
methods that let you get the first and the last key or a submap based on a criteria, etc. Those methods are as follows:
Comparator<? super K> comparator() : It returns the Comparator object used for custom
sorting of the keys in the SortedMap . If you have not used a Comparator object, it returns null
and natural ordering will be used based on the implementation of the Comparable interface
for the keys.
K firstKey() : It returns the key of the first entry in the SortedMap . If the SortedMap is empty,
it throws a NoSuchElementException .
 
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