Factory method to create immutable Map in Java 9

In Java 9 there are some features are added in Java language and factory method for immutable map is one of them.
Characteristics of immutable map:

• As the name suggest these map are immutable.
• If any attempt made to add, delete and update elements in the map we will have UnsupportedOperationException.
• Immutable map do not allow null element either.
• If any attempt made to create a immutable map with null element, we will have NullPointerException. If any attempt made to add null element in map, we will have UnsupportedOperationException.

Creating immutable map in Java 8

To create immutable map in java 8, we use java.util.unmodifiableMap(Map map) method. unmodifiableMap(Map map): This method returns an unmodifiable view of the specified map. This method allows modules to provide users with “read-only” access to internal maps.

Syntax: public static  Map unmodifiableMap(Map map)
Returns: an unmodifiable view of the specified map.
Exception: NA

Java code for immutable empty and no-empty map:

// Java code illustrating immutable map in java 8
import java.util.*;
class ImmutableListDemo
{
    public static void main(String args[])
    {
        // empty map
        Map<Integer, String> empty = new HashMap();
        Map immutable1 = Collections.unmodifiableMap(empty);

        // non-empty map
        Map<Integer, String> non_empty = new HashMap();
        non_empty.put(1, "ide");

        Map immutable2 = Collections.unmodifiableMap(non_empty);

        // adding key-value pair in these immutable map
        immutable1.put(1,"gfg");
        immutable2.put(2,"quiz");

    }
}

Above code will generate exception, because we are trying to add key-value pair in immutable Map.

Runtime Error : Exception in thread "main" 
java.lang.UnsupportedOperationException
at java.util.Collections$UnmodifiableMap.put(Collections.java:1457)
at ImmutableListDemo.main(File.java:17)

Creating immutable Map in java 9

To create immutable map in java 9, we use of() and ofEntries() method.
Java code to create immutable map in java 9:

// Java code illustrating of() method
import java.util.*;
class ImmutableListDemo
{
    public static void main(String args[])
    {
        // empty immutable map
        Map<Integer, String> immutable1 = Map.of();

        // non-empty immutable map
        Map<Integer, String> immutable2 = Map.of(1, "ide",2, "quiz");

        // adding key-value pair in these immutable map
        immutable1.put(1,"gfg");
        immutable2.put(3,"contribute");

    }
}

After running above code, we will have UnsupportedOperationException.
Java code to create immutable map using Map.ofEntries() method in Java 9:

// Java code illustrating ofEntries method
import java.util.*;
import java.util.Map.Entry;
class ImmutableListDemo
{
    public static void main(String args[])
    {
        // empty immutable map
        Map<Integer, String> immutable = Map.ofEntries();

        // non-empty immutable map
        Map.Entry<Integer, String> entry1 = Map.entry(1, "gfg");
        Map.Entry<Integer, String> entry2 = Map.entry(2, "contribute");

        Map<Integer, String> immubatleMap = Map.ofEntries(entry1,
                         entry2);
    }
}

So of() and ofEntries() are method used to create immutable map in java 9.

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