Convenience Factory Methods for Collections

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Convenience Factory Methods for Collections, added in JDK 9 (JEP 269), were a set of methods designed to make the instantiation of collections easier.

Verbosity When Creating Collections

Creating even simple collections, like the below ArrayList example required a fair amount of typing to accomplish:

List<String> values = 
	new ArrayList<>();
values.add("value 1");
values.add("value 2");
values.add("value 3");

Collections of

To lower the formality around creating simple collections List, Set, and Map each had a default method of defined for creating an unmodifiable instance of the respective collection type like in the examples below for List and Set:

List:

List<String> values = List.of(
	"value 1", 
	"value 2", 
	"value 3");

Set:

Set<String> values = Set.of(
	"value 1", 
	"value 2", 
	"value 3");

Map.of

When creating a Map instance using Map.of the types of arguments passed into of must match the key and value of the the map like in the below example of Integer and String:

Map<Integer, String> values = Map.of(
	1, "value 1", 
	2, "value 2", 
	3, "value 3");

Map ofEntries

If more clarity is needed when creating a simple Map instance, you could also use Map.ofEntries with java.util.Map.entry, like in the below example:

import static java.util.Map.entry;

...
Map<Integer, String> values = Map.ofEntries(
	entry(1, "value 1"), 
	entry(2, "value 2"), 
	entry(3, "value 3"));
...

Happy coding!