In this tutorial, we will learn how to make immutable HashMap with an example.
We will see two examples to make immutable HashMap:
We will see two examples to make immutable HashMap:
- First, we will see how to create an immutable HashMap using Collections.unmodifiableMap() method with an example.
- Second, we will see how to create an immutable HashMap using Java 9 provided Map.ofEntries() static factory method.
Create Immutable HashMap with Collections.unmodifiableMap() Method
Prior to Java 9, we create an immutable HashMap using Collections.unmodifiableMap() method like:public class ImmutableMapExample {
public static void main(String[] args) {
// Creating a HashMap
Map < String, Integer > numberMapping = new HashMap < > ();
// Adding key-value pairs to a HashMap
numberMapping.put("One", 1);
numberMapping.put("Two", 2);
numberMapping.put("Three", 3);
Collections.unmodifiableMap(numberMapping);
System.out.println(fruits);
}
}
Output:
{One=1, Two=2, Three=3}
Create immutable HashMap with Java 9 Map.ofEntries() factory method
The below example shows how to create an immutable HashMap using Java 9 provided Map.ofEntries() static factory method.import java.util.HashMap;
import java.util.Map;
public class ImmutableHashMap {
public static void main(String[] args) {
Map < String, String > fruits = new HashMap < String, String > ();
fruits.put("1", "Banana");
fruits.put("2", "Mango");
fruits.put("3", "Apple");
// java 9 with factory methods
Map < String, String > map = Map.ofEntries(
Map.entry("1", "Banana"),
Map.entry("2", "Mango"),
Map.entry("3", "Apple"));
System.out.println(map);
}
}
Output:
{1=Banana, 2=Mango, 3=Apple}
Conclusion
In this tutorial, we have seen how to make immutable HashMap using Collections.unmodifiableMap() method and Java 9 provided Map.ofEntries() static factory method with an example.
References
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