The keySet() in Hashmap is used to get a set of the keys present in a hashmap.
Method signature:
The signature for keySet() is shown below:
public Set keySet()
Methods parameters and return type:
Parameter: It doesn’t take any parameters.
Return type: It returns a set of keys.
Throws: N/A.
Hashmap keySet() Example:
In this example, we have displayed a key set of a hashmap by using this method.
Source code:
public class Example1 {
public static void main(String[] args) {
HashMap<Integer, String> map = new HashMap<>();
Set set = new HashSet<>();
map.put(1, "1");
map.put(10, "2");
map.put(100, "3");
map.put(1000, "4");
map.put(10000, "5");
System.out.println("The hashmap is: "+map);
set = map.keySet();
System.out.println("The key set is: "+set);
}
}
Output:
run:
The hashmap is: {10000=5, 1=1, 100=3, 1000=4, 10=2}
The key set is: [10000, 1, 100, 1000, 10]
BUILD SUCCESSFUL (total time: 0 seconds)
Example 2:
In this example, we have used keySet() on an empty hashmap, and it returns us an empty set without generating any exception.
Source code:
public class Example2 {
public static void main(String[] args) {
HashMap<Integer, String> map = new HashMap<>();
Set set = new HashSet<>();
set = map.keySet();
System.out.println("The key set is: "+set);
}
}
Output:
run:
The key set is: []
BUILD SUCCESSFUL (total time: 1 second)