Java 10 was one of the fastest release of a new Java version. It was released just 6 months after Java 9. Starting this release Java moved to a 6 month release model, meaning a Java version will be released every 6 months. Release months would be March and September.

New Java 10 features

Some of the main features introduced in Java 10 are following:

JEP 322: Time-Based Release Versioning

With the new release cycle, java introduced a new versioning model. New versioning as follows.

$FEATURE.$INTERIM.$UPDATE.$PATCH

$FEATURE: Feature release counter. This is the main java version, eg. for Java 10 it’s 10. It will changes with every new release of java eg. for Java 11, 12, and so on. This was formerly called $MAJOR version in earlier releases.

$INTERIM: It is the interim release counter, for non feature releases. In the current release model this will always be 0. It was added to make this versioning system future proof. This was formerly called $MINOR.

$UPDATE: It is the update release counter. Its increased when fixes to security issues, regressions, and bugs in newer features are added to release. This was formerly called $SECURITY. This will increment 1 month after $FEATURE is incremented and then every 3 months after that. Eg. March 2018 release was 10.0.0, April 2018 release was 10.0.1 , July 2018 release was 10.0.2 and so on.

$PATCH: It is the emergency patch-release counter. Its incremented only when there is an emergency release to fix a critical issue.

You can see your java version on command line

root@5843268d0e41:/# java -version
openjdk version "10.0.2" 2018-07-17
OpenJDK Runtime Environment (build 10.0.2+13-Debian-2)
OpenJDK 64-Bit Server VM (build 10.0.2+13-Debian-2, mixed mode)

There were some changes to Version Class to support the new release versioning. Following new methods were introduced:

int 	feature()
int 	hashCode()
int 	interim()

root@5843268d0e41:/# jshell
jshell> import java.lang.Runtime.Version

jshell> Version version = Runtime.version();
version ==> 10.0.2+13-Debian-2

jshell> version.feature()
$3 ==> 10

jshell> version.interim()
$4 ==> 0

jshell> version.update()
$5 ==> 2

jshell> version.patch()
$6 ==> 0

JEP 286: Local-Variable Type Inference

Type inference of local variables is a very exciting feature. Similar feature is present in languages like C# and go since some time. Its addition to java is a welcome change.

Idea behind this feature is to make code both easier to type and read. Type inferred variables are created using var keyword. For eg.

Java 9 (no type inference)

List<Integer> list = List.of(1,2);
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
List<Map<String,String>> listOfMaps = List.of(Map.of("k1","v1"),Map.of("k2","v2"));

Java 10 (using type inference)

var intList = List.of(1,2);
var outputStream = new ByteArrayOutputStream();
var listOfMaps = List.of(Map.of("k1","v1"),Map.of("k2","v2"));

You can see above using var keyword improves the readability, as information on left hand side of equals is often repeated on right hand side

Rules of using type inference

  • Type inference can be only used for
    • Local variables with initializers.
    • Index variable in enhanced for-loop and traditional for-loop.

Tips and Traps

  • When declaring variable always assign a value. 
    var a        // error : cannot use 'var' on variable without initializer
var a = null // error : variable initializer is 'null'
var a = 1    // good
  • Lambda or method reference is not a valid value. 
    var b = ()->5;         // error: lambda expression needs an explicit target-type
var b = Object::equals // error: method reference needs an explicit target-type
  • Array initializer should be explicit. 
    var arr = { 1, 2 }    // error array initializer needs an explicit target-type
var arr = new int[]{ 1, 2 } // good

  • Take care when using diamond or Generic methods

    var list = List.of(1,2);  // infers List<Integer>
var list = List.of();     // infers List<Object>

var students = new ArrayList<Students>(); // infers ArrayList<Students>
var students = new ArrayList<>(); // infers ArrayList<Object>
  • Numeric literals can silently widened or narrowed
byte flag = 0
long longValue = 1

// unexpected widening or narrowing
var flag = 0 // inferred as int
var longValue = 1 // inferred as int.

You can see in general using type-inference reduces clutter and improves readability, but it should be used with care to avoid unforeseen side affects.

Api changes

New orElseThrow method in Optional class

A new method orElseThrow has been added to the Optional class. This works exactly same as already existing get method in Optional class. It just highlights the fact that an exception (NoSuchElementException) is thrown if optional is empty.

Use of orElseThrow is preferred over get method

jshell> Optional optional = Optional.of(1)
optional ==> Optional[1]

jshell> optional.orElseThrow()
$2 ==> 1

jshell> optional.get()
$3 ==> 1

jshell> Optional optional2 = Optional.empty()
optional2 ==> Optional.empty

jshell> optional2.orElseThrow()
|  java.util.NoSuchElementException thrown: No value present
|        at Optional.orElseThrow (Optional.java:371)
|        at (#6:1)

jshell> optional2.get()
|  java.util.NoSuchElementException thrown: No value present
|        at Optional.get (Optional.java:148)
|        at (#8:1)

Apis for Creating Unmodifiable Copy of Collections

  • List.copyOf, Set.copyOf, and Map.copyOf methods create new unmodifiable collection instances from existing instances.

    jshell>   List<Integer> list1 = new ArrayList<>();
list1 ==> []

jshell>   list1.add(1);
$10 ==> true

jshell>   var list2 = List.copyOf(list1)
list2 ==> [1]
// list2 is unmodifiable.
jshell> list2.add(2)
|  java.lang.UnsupportedOperationException thrown
|        at ImmutableCollections.uoe (ImmutableCollections.java:71)
|        at ImmutableCollections$AbstractImmutableList.add (ImmutableCollections.java:77)
|        at (#12:1)

New Apis for Creating Unmodifiable Collections from Stream

New methods toUnmodifiableList, toUnmodifiableSet, and toUnmodifiableMap have been added to the Collectors class in the Stream package.

Before Java 10 we could create a list from a Stream using Collectors.toList() method. This list could be modified.

jshell> var list1 = Stream.of(1,2,3).collect(Collectors.toList());
list1 ==> [1, 2, 3]

jshell> list1.add(4)
$18 ==> true

Using the newer api methods we can create an unmodifiable collection.

jshell> var list1 = Stream.of(1,2,3).collect(Collectors.toUnmodifiableList());
list1 ==> [1, 2, 3]

jshell> list1.add(4)
|  java.lang.UnsupportedOperationException thrown
|        at ImmutableCollections.uoe (ImmutableCollections.java:71)
|        at ImmutableCollections$AbstractImmutableList.add (ImmutableCollections.java:77)
|        at (#21:1)

Similarly we can also create unmodifiable sets and maps.