Java SE 9: Factory Methods for Immutable Set with Examples [Latest]

• Introduction
• Java SE 8: Immutable Empty Set
• Java SE 9: Immutable Empty Set
• Java SE 8: Immutable Non-Empty Set
• Java SE 9: Immutable Non-Empty Set
• Java SE 9: Immutable Non-Empty Set With Var-Args

Introduction

Oracle Corporation is going to release Java New Version: Java SE 9 around March 2017. So, I would like to deliver a series of Posts on Java SE 9 New Features. It is my sixth post in this series.

I have already delivered couple of posts on Java SE 9 New Features. Before going through this post, please read them. It is the continuation of my previous post: Java SE 9: Factory Methods for Immutable List.

In this post, we are going to discuss one more Java SE 9 New Feature: “Factory Methods for Immutable Set” with some simple and suitable examples.

Java SE 8: Immutable Empty Set

In Java SE 8 and earlier Versions, if we want to create an empty Immutable or Unmodifiable Set, we should use Collections class utility method: unmodifiableSet as shown below:

Empty Set Example:-

 Set<String> emptySet = new HashSet<>();
 Set<String> immutableSet = Collections.unmodifiableSet(emptySet);

Here we can observe that it is very tedious and verbose process. Let us see the same thing in Java SE 9 now.

NOTE:- Diamond Operator does NOT work in Java SE 6 and earlier versions. Rest of the code is same for all Java versions.

Java SE 9: Immutable Empty Set

To overcome those shortcomings, Java SE 9 has introduced a couple of useful methods in Set interface so that we do not need to use all these tedious steps to create Immutable Empty Set.

If we go through the Java SE 9 Set API, we can find the below method signature in Set interface.
Empty Set API Utility

 static <E> Set<E> of()

It is used to create an empty Immutable Set (a Set with zero elements).

Empty Set Example:-

 Set<String> immutableSet = Set.of();

Here we can observe that it is very easy to create an empty Immutable Set in Java SE 9.

Java SE 8: Immutable Non-Empty Set

In this section, we will see how to create Immutable Non-Empty Set in Java SE 8 and earlier Versions. We use same unmodifiableSet method from Collections class to create an Immutable Non-Empty Set as shown below:

Non-Empty Set Example:-

 Set<String> nonemptySet = new HashSet<>();
 nonemptySet.add("one");
 nonemptySet.add("two");
 nonemptySet.add("three");
 Set<String> immutableSet = Collections.unmodifiableSet(nonemptySet);

NOTE:- Diamond Operator does NOT work in Java SE 6 and earlier versions. Rest of the code is same for all Java versions.

Here we can observe that it is very tedious and verbose process. Let us see the same thing in Java SE 9 now.

Java SE 9: Immutable Non-Empty Set

In this section, we will see how to create Immutable Non-Empty Set in Java SE 9 Version. If we go through the Java SE 9 Set Interface API, we will see a set of overloaded methods as shown below:

Non-Empty Set API Utility

static <E> Set<E> of(E e1)
static <E> Set<E> of(E e1,E e2)
static <E> Set<E> of(E e1,E e2,E e3)
static <E> Set<E> of(E e1,E e2,E e3,E e4)
static <E> Set<E> of(E e1,E e2,E e3,E e4,E e5)
static <E> Set<E> of(E e1,E e2,E e3,E e4,E e5,E e6)
static <E> Set<E> of(E e1,E e2,E e3,E e4,E e5,E e6,E e7)
static <E> Set<E> of(E e1,E e2,E e3,E e4,E e5,E e6,E e7,E e8)
static <E> Set<E> of(E e1,E e2,E e3,E e4,E e5,E e6,E e7,E e8,E e9)
static <E> Set<E> of(E e1,E e2,E e3,E e4,E e5,E e6,E e7,E e8,E e9,E e10)

Non-Empty Set Example:-

 Set<String> immutableSet = Set.of("one","two","three");

It is very simple and no-verbosity in this code right. Very nice stuff!

Test the above code in Java SE 9 REPL:

jshell> Set<String> immutableSet = Set.of("one","two","three")
immutableSet ==> [one, two, three]

Here we can observe that it is very easy to create an Non-empty Immutable Set in Java SE 9.

Java SE 9: Immutable Non-Empty Set With Var-Args

Oracle Corp has introduced one more Set.of() method with Var-args syntax. The following is a Var-Args method (Variable Number of arguments method) used to create an Non-empty Immutable Set in Java SE 9:

static <E> Set<E> of(E... elements)

It is used to create an Immutable Set with array of elements as shown below:

Non-Empty Set Example:-

 String[] nameArr =  { "one", "two", "three"};
 Set<String[]> set= Set.<String[]>of(nameArr);

Test this with Java SE 9 REPL:

jshell> String[] nameArr =  { "one", "two", "three"}
nameArr ==> String[3] { "one", "two", "three" }
jshell> Set<String[]> set = Set.<String[]>of(nameArr);
set ==> [[Ljava.lang.String;@56ef9176]
jshell> set
set ==> [[Ljava.lang.String;@56ef9176]

Here we have created an Immutable Set with Array of String Elements.

NOTE:-
Characteristics of a Immutable Set are similar to Immutable List. You can find those information in detail here: Java SE 9: Factory Methods for Immutable List.

That’s it all about “Java SE 9: Factory Methods for Immutable Set” concept. We will discuss some more Java SE 9 New Features in my coming posts.

Please drop me a comment if you like my post or have any issues/suggestions/type errors.

Thank you for reading my tutorials.

Happy Java SE 9 Learning!