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