Collection Factory Methods

Java added some factory methods to the List, Set, and Map interface in Java 9 version. These methods are useful to create an immutable collection with a simple and concise code.

List interface Factory Methods

Example: List

In this example, we are creating an immutable list by using the factory method of List interface.

import java.util.List;

public class Main { 
	public static void main(String[] args){  
        List<String> fruits = List.of("Orange","Mango","Apple");
        System.out.println(fruits);
        // Traversing using for-each
        for (String fruit : fruits) {
			System.out.println(fruit);
		}
	}
}

[Orange, Mango, Apple]
Orange
Mango
Apple

Set interface Factory Methods

Like the List interface, the Set interface also contains factory methods to create an immutable set. The following is the table of factory methods of the Set interface.

Example: Set

In this example, we are using the factory method of Set interface to create an immutable set.

public class Main { 
	public static void main(String[] args){  
        Set<String> fruits = Set.of("Orange","Mango","Apple");
        System.out.println(fruits);
        // Traversing using for-each
        for (String fruit : fruits) {
			System.out.println(fruit);
		}
	}
}

[Orange, Mango, Apple]
Orange
Mango
Apple

Map Interface Factory Methods

The following is a table of Map interface factory methods.

Example: Map

In this example, we are creating an immutable map by using the factory method.

import java.util.Map;

public class Main { 
	public static void main(String[] args){  
        Map<Integer,String> fruits = Map.of(101,"Orange",102,"Mango",103,"Apple");
        System.out.println(fruits);
        // Traversing using for-each
        for(Map.Entry<Integer, String> m : fruits.entrySet()){    
			System.out.println(m.getKey()+" "+m.getValue());
		}
	}
}

{102=Mango, 101=Orange, 103=Apple}
102 Mango
101 Orange
103 Apple

Example 2: Map Factory Method

import java.util.Map;

public class Main { 
	public static void main(String[] args){  
		Map<Integer, String> fruits = Map.ofEntries(
                Map.entry(101,"Orange"),
                Map.entry(102, "Apple"),
                Map.entry(103, "Mango"));
        System.out.println(fruits);
        // Traversing using for-each
        for(Map.Entry<Integer, String> m : fruits.entrySet()){    
			System.out.println(m.getKey()+" "+m.getValue());
		}
	}
}

{102=Apple, 103=Mango, 101=Orange}
102 Apple
103 Mango
101 Orange