Convenience Factory Methods for Collections

With the introduction of functional programming in Java, the interest in and need for immutable objects increased. The functions passed into the methods may be executed in substantially different contexts than the one they were created in, so the need to decrease the chances of unexpected side effects made the case for immutability stronger. Besides, the Java way of creating an unmodifiable collection was quite verbose anyway, so the issue was addressed in Java 9. Here is an example of the code that creates an immutable collection of the Set interface in Java 8:

Set<String> set = new HashSet<>();
set.add("Life");
set.add("is");
set.add("good!");
set = Collections.unmodifiableSet(set); 

After one does it several times, the need for a convenience method comes up naturally as the basic refactoring consideration that always lingers in the background thinking of any software professional. In Java 8, the previous code could be changed to the...