The EnumMap.containsKey()
method in Java is used to check if a specific key is present in the map. This guide will cover the method’s usage, explain how it works, and provide examples to demonstrate its functionality using enum constants as keys. We will also cover a real-world use case to show how EnumMap.containsKey()
can be used effectively.
Table of Contents
- Introduction
containsKey
Method Syntax- Examples
- Basic Usage of
containsKey
Method - Handling Non-Existent Keys
- Basic Usage of
- Real-World Use Case
- Example: Checking Task Assignment for a Specific Day
- Conclusion
Introduction
The EnumMap.containsKey()
method is a member of the EnumMap
class in Java. It allows you to check if a specific key is present in the map. This method returns true
if the map contains a mapping for the specified key, and false
otherwise.
containsKey() Method Syntax
The syntax for the containsKey
method is as follows:
public boolean containsKey(Object key)
- Parameters:
key
: The key whose presence in this map is to be tested.
- Returns:
true
if this map contains a mapping for the specified key,false
otherwise.
Examples
Basic Usage of containsKey
Method
The containsKey
method can be used to check if a specific key is present in an EnumMap
.
Example
import java.util.EnumMap;
public class EnumMapContainsKeyExample {
// Define an enum representing days of the week
enum Day {
MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
}
public static void main(String[] args) {
// Create an EnumMap with Day as key and String as value
EnumMap<Day, String> tasks = new EnumMap<>(Day.class);
// Adding entries to the EnumMap
tasks.put(Day.MONDAY, "Go to gym");
tasks.put(Day.TUESDAY, "Attend meeting");
tasks.put(Day.WEDNESDAY, "Work from home");
// Checking if WEDNESDAY is present in the EnumMap
boolean hasWednesday = tasks.containsKey(Day.WEDNESDAY);
// Printing the result
System.out.println("Is WEDNESDAY present? " + hasWednesday);
}
}
Output:
Is WEDNESDAY present? true
Handling Non-Existent Keys
If the specified key is not present in the EnumMap
, the containsKey
method returns false
.
Example
import java.util.EnumMap;
public class EnumMapNonExistentKeyExample {
enum Day {
MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
}
public static void main(String[] args) {
// Create an EnumMap with Day as key and String as value
EnumMap<Day, String> tasks = new EnumMap<>(Day.class);
// Adding entries to the EnumMap
tasks.put(Day.MONDAY, "Go to gym");
tasks.put(Day.TUESDAY, "Attend meeting");
// Checking if SUNDAY is present in the EnumMap
boolean hasSunday = tasks.containsKey(Day.SUNDAY);
// Printing the result
System.out.println("Is SUNDAY present? " + hasSunday);
}
}
Output:
Is SUNDAY present? false
Real-World Use Case
Example: Checking Task Assignment for a Specific Day
A common real-world use case for EnumMap.containsKey()
is checking if a task has been assigned for a specific day of the week.
Example
import java.util.EnumMap;
public class TaskChecker {
enum Day {
MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
}
public static void main(String[] args) {
// Create an EnumMap to manage tasks for each day
EnumMap<Day, String> tasks = new EnumMap<>(Day.class);
// Adding tasks for each day
tasks.put(Day.MONDAY, "Go to gym");
tasks.put(Day.TUESDAY, "Attend meeting");
tasks.put(Day.WEDNESDAY, "Work from home");
tasks.put(Day.THURSDAY, "Team lunch");
tasks.put(Day.FRIDAY, "Project presentation");
// Checking if a task is assigned for SATURDAY
boolean hasTaskForSaturday = tasks.containsKey(Day.SATURDAY);
// Printing the result
System.out.println("Is there a task assigned for SATURDAY? " + hasTaskForSaturday);
}
}
Output:
Is there a task assigned for SATURDAY? false
In this example, EnumMap.containsKey()
is used to check if a task has been assigned for a specific day, making it easy to verify task assignments.
Conclusion
The EnumMap.containsKey()
method in Java provides a way to check if a specific key is present in the map. By understanding how to use this method, you can efficiently manage and verify the presence of keys in collections where the keys are enum constants. This method allows you to check for the existence of entries in an EnumMap
, making it a versatile tool for managing data in various scenarios.