The HashMap.containsKey()
method in Java is used to check if a specific key is present in a HashMap
.
Table of Contents
- Introduction
containsKey
Method Syntax- Examples
- Checking for the Presence of Keys in a HashMap
- Real-World Use Case: Verifying Employee IDs
- Conclusion
Introduction
The HashMap.containsKey()
method is a member of the HashMap
class in Java. It allows you to check if a specific key exists in the HashMap
. This can be useful when you need to verify the existence of a key before performing operations that depend on the presence of that key.
containsKey() Method Syntax
The syntax for the containsKey
method is as follows:
public boolean containsKey(Object key)
- The method takes a single parameter
key
of typeObject
, which represents the key to be checked for presence in theHashMap
. - The method returns a boolean value:
true
if theHashMap
contains a mapping for the specified key.false
if theHashMap
does not contain a mapping for the specified key.
Examples
Checking for the Presence of Keys in a HashMap
The containsKey
method can be used to check if a specific key is present in a HashMap
.
Example
import java.util.HashMap;
import java.util.Map;
public class ContainsKeyExample {
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");
// Checking for the presence of keys in the HashMap
boolean containsIndia = countries.containsKey("India");
boolean containsBrazil = countries.containsKey("Brazil");
// Printing the results
System.out.println("HashMap contains key 'India': " + containsIndia);
System.out.println("HashMap contains key 'Brazil': " + containsBrazil);
}
}
Output:
HashMap contains key 'India': true
HashMap contains key 'Brazil': false
Real-World Use Case: Verifying Employee IDs
In a real-world scenario, you might use the containsKey
method to verify if an employee ID exists in a company’s employee database before performing operations such as updating employee details or processing payroll.
Example
import java.util.HashMap;
import java.util.Map;
public class EmployeeIDVerification {
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");
// Employee ID to be searched
String employeeIdToSearch = "E002";
// Checking if the employee ID exists in the database
if (employeeDatabase.containsKey(employeeIdToSearch)) {
System.out.println("Employee ID " + employeeIdToSearch + " exists. Employee Name: " + employeeDatabase.get(employeeIdToSearch));
} else {
System.out.println("Employee ID " + employeeIdToSearch + " does not exist.");
}
}
}
Output:
Employee ID E002 exists. Employee Name: Priya Sharma
Conclusion
The HashMap.containsKey()
method in Java provides a way to check if a specific key is present in a HashMap
. By understanding how to use this method, you can efficiently verify the presence of keys and make decisions based on their existence. This method is useful when you need to ensure that a key exists before performing operations that depend on its presence, such as updating records or processing transactions.