Class CollectionFactoryExamples

java.lang.Object

net.jrodolfo.java_evolution.java09.CollectionFactoryExamples

public class CollectionFactoryExamples
extends Object

Demonstrates collection factory methods introduced in Java 9.

Before Java 9, creating a small read-only collection usually required several steps: create a mutable collection, populate it, and wrap it with an unmodifiable view. That made simple constants and test data noisier than the values being represented.

List.of(Object[]), Set.of(Object[]), and Map.of(Object, Object) solve that problem for small collections. They are compact, reject null, reject duplicate set elements or map keys, and return collections that cannot be mutated. The JDK can also use specialized internal implementations for small immutable collections, which is one reason these factories are preferable to hand-built wrappers for constants and examples.

Constructor Summary

Constructors

Constructor	Description
CollectionFactoryExamples()

Method Summary

Modifier and Type	Method	Description
Set<String>	languageFeatureCategories()	Creates an immutable set.
List<String>	languageFeatures()	Creates an immutable list.
List<String>	listWithNullValue()	Shows that factory collections reject null.
Map<Integer,String>	mapWithDuplicateKeys()	Shows that Map.of(Object, Object, Object, Object) rejects duplicate keys.
Map<Integer,String>	releaseNamesByVersion()	Creates an immutable map.
Set<String>	setWithDuplicateValues()	Shows that Set.of(Object[]) rejects duplicates.

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

CollectionFactoryExamples

public CollectionFactoryExamples()

Method Details

languageFeatures

public List<String> languageFeatures()

Creates an immutable list.

Returns:

a list created with List.of(Object[])

languageFeatureCategories

public Set<String> languageFeatureCategories()

Creates an immutable set.

Returns:

a set created with Set.of(Object[])

releaseNamesByVersion

public Map<Integer,String> releaseNamesByVersion()

Creates an immutable map.

Returns:

a map created with Map.of(Object, Object, Object, Object)

listWithNullValue

public List<String> listWithNullValue()

Shows that factory collections reject null.

Returns:

never returns because List.of(Object[]) throws

setWithDuplicateValues

public Set<String> setWithDuplicateValues()

Shows that Set.of(Object[]) rejects duplicates.

Returns:

never returns because the set contains duplicate values

mapWithDuplicateKeys

public Map<Integer,String> mapWithDuplicateKeys()

Shows that Map.of(Object, Object, Object, Object) rejects duplicate keys.

Returns:

never returns because the map contains duplicate keys