What factory methods have been added for collections in Java 9?

Factory method is a special type of static method that can be used to create unmodifiable collection instances . This means that we can use these methods to create lists, sets and maps containing a small number of elements.

List.of()

List.of() is a static factory method that provides a convenient way to create immutableList.

Syntax

<strong>List.of(elements...)</strong>

Example

import java.util.List;
public class ListTest {
   public static void main(String[] args) {
      <strong>List<String></strong> list =<strong> List.of</strong>("item 1", "item 2", "item 3", "item 4", "item 5");
      for(String l : list) {
         System.out.println(l);
      }
   }
}

Output

<strong>item 1
item 2
item 3
item 4
item 5</strong>

##Set.of() method

Set.of() is a static factory method that provides a convenient way to create immutable sets.

Syntax

<strong>Set.of(elements...)
</strong>

Example

import java.util.Set;
public class SetTest {
   public static void main(String[] args) {
      <strong>Set<String></strong> set = <strong>Set.of</strong>("Item 1", "Item 2", "Item 3", "Item 4", "Item 5");
      for(String s : set) {
         System.out.println(s);
      }
   }
}

Output

<strong>Item 5
Item 1
Item 2
Item 3
Item 4</strong>

##Map.of() and Map. ofEntries() method

The

Map.of()

and Map.ofEntries() are static factory methods that provide a convenient way to create Immutable Mapping. Syntax

<strong>Map.of(k1, v1, k2, v2)
Map.ofEntries(entry(k1, v1), entry(k2, v2),...)</strong>

Example

import java.util.Map;
public class MapTest {
   public static void main(String[] args) {
      <strong>Map<Integer, String></strong> map = <strong>Map.of</strong>(101, "Raja", 102, "Adithya", 103, "Jai");
      for(<strong>Map.Entry<Integer, String></strong> m : map.<strong>entrySet()</strong>) {
         System.out.println(m.getKey() + " " + m.getValue());
      }
   }
}

Output

<strong>103 Jai
102 Adithya
101 Raja</strong>

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