The HashMap.keySet()
method in Java is used to obtain a set view of the keys contained in the HashMap
.
Table of Contents
- Introduction
keySet
Method Syntax- Examples
- Iterating Over Keys in a HashMap
- Real-World Use Case: Displaying Employee IDs
- Conclusion
Introduction
The HashMap.keySet()
method is a member of the HashMap
class in Java. It allows you to obtain a set view of the keys contained in the HashMap
. This can be useful for iterating over the keys or performing bulk operations on the keys.
keySet() Method Syntax
The syntax for the keySet
method is as follows:
public Set<K> keySet()
- The method does not take any parameters.
- The method returns a
Set
view of the keys contained in theHashMap
.
Examples
Iterating Over Keys in a HashMap
The keySet
method can be used to obtain a set view of the keys in a HashMap
, which can then be iterated over.
Example
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
public class KeySetExample {
public static void main(String[] args) {
// Creating a Map with String keys and String values
Map<String, String> countries = new HashMap<>();
// Adding entries to the HashMap
countries.put("India", "IN");
countries.put("United States", "US");
countries.put("Canada", "CA");
// Getting the set view of the keys
Set<String> keys = countries.keySet();
// Iterating over the keys
for (String key : keys) {
System.out.println("Key: " + key);
}
}
}
Output:
Key: India
Key: United States
Key: Canada
Real-World Use Case: Displaying Employee IDs
In a real-world scenario, you might use the keySet
method to display employee IDs stored in an employee database.
Example
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
public class DisplayEmployeeIDs {
public static void main(String[] args) {
// Creating a Map with String keys (employee IDs) and String values (employee names)
Map<String, String> employeeDatabase = new HashMap<>();
// Adding entries to the HashMap
employeeDatabase.put("E001", "Ravi Kumar");
employeeDatabase.put("E002", "Priya Sharma");
employeeDatabase.put("E003", "Vijay Singh");
// Getting the set view of the keys
Set<String> employeeIDs = employeeDatabase.keySet();
// Iterating over the keys to display employee IDs
for (String employeeID : employeeIDs) {
System.out.println("Employee ID: " + employeeID);
}
}
}
Output:
Employee ID: E001
Employee ID: E002
Employee ID: E003
Conclusion
The HashMap.keySet()
method in Java provides a way to obtain a set view of the keys contained in the HashMap
. By understanding how to use this method, you can efficiently iterate over the keys and perform bulk operations on the keys in the map. This method is useful for displaying keys, performing operations on each key, and managing collections of keys in various applications.