Factory method to create immutable Map in Java 9 Last Updated : 11 Dec, 2018 Comments Improve Suggest changes Like Article Like Report 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 // 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 // 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 // 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. Comment More infoAdvertise with us Next Article Factory method to create immutable Map in Java 9 A Abhishek Verma Improve Article Tags : Misc Java Practice Tags : JavaMisc Similar Reads Factory method to create Immutable Set in Java 9 Java 9 was released around march 2017 and please install jdk 9, it will be helpful in understanding the code used in this article. 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