This method is used to return a Set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa.
Syntax:
Set keySet()
Parameters: This method has no argument.
Returns: This method returns a set containing keys of the specified map.
Below programs show the implementation of int keySet() method.
Program 1:
// Java code to show the implementation of// isEmpty method in Map interfaceimport java.util.*;public class GfG {      // Driver code    public static void main(String[] args)    {          // Initializing a Map of type HashMap        Map<String, String> map = new HashMap<>();          System.out.println(map);          System.out.println(map.isEmpty());    }} |
Output:
{}
true
Program 2: Below is the code to show implementation of hashCode().
// Java code to show the implementation of// keySet method in Map interfaceimport java.util.*;public class GfG {      // Driver code    public static void main(String[] args)    {          // Initializing a Map of type HashMap        Map<Integer, String> map = new HashMap<>();        Set<Integer> s = new HashSet<>();        map.put(1, "One");        map.put(3, "Three");        map.put(5, "Five");        map.put(7, "Seven");        map.put(9, "Nine");        System.out.println(map);        s = map.keySet();        System.out.println(s);    }} |
Output:
{1=One, 3=Three, 5=Five, 7=Seven, 9=Nine}
[1, 3, 5, 7, 9]
Reference:
Oracle Docs
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