Changes from Java 8 to Java 11

Java 8 to Java 11


First, there are changes about the language.

var You can now type infer about local variables.

var a = "Foo";

I think the following is a good guideline.

--For those with types on the right side, such as new and List.of, it is better to use var (other than ʻInteger, Long, etc.) --You can use var for basic classes such as java.langandjava.util --It is better not to usevar because wrapper classes such as ʻInteger and Long are handled with caution. --You can use var for the basic type --Don't use var for application classes

When using a variable of the wrapper class, it handles null, so I think it is better to specify the type. If you don't use null, use the basic type. When applied to item 1, the following writing style is OK.

var count = Long.valueOf("123");

However, for ʻIntegerandLongmethods, there are some that return the basic type and some that return the wrapper type, so it is safer to specify the type. If you receive it withvar`, it is better to make it a basic type.

private interface methods

You can now use private methods for interface.

Since the static method and default method can be used in Java8, the common processing can be written in private.

effective final in try-with-resource

For variables that are practically final, you can now specify only variables with try-with-resource. Until now, if you wanted to automatically close a Closable variable defined outside try with try-with-resource, you had to assign it to another variable. For example, if you want to use it finally, you need to define a variable outside of try, but you can use it in such a case.

var io = new InputStream();
try (var io2 = io) {

var io = new InputStream();
try (io) {

<> in anonymous You can now type infer anonymous classes with the diamond operator.

List<String> strs = new ArrayList<>() {{

_ Not available

You can no longer use _ as a variable.


From here, we will summarize the changes in the standard library for each class.

Click here for Java 11 API


String Compact String It is included in Java 9. Until Java8, characters were held as char in UTF-16, so 2 bytes were used for each character, but character strings containing only ASCII characters such as alphabets and numbers are now held in 1 byte.

Indy String concatenation

Until now, string concatenation with + was expanded to StringBuilder, but it will be confirmed at runtime with Invoke Dynamic.

"aa"+ a

new StringBuilder("aa").append(a);

↓ Dynamic Invoke

repeat(n) Can be repeated

jshell> "test".repeat(3)
$1 ==> "testtesttest"


isBlank is a UTF space character

strip() / stripLeading() / stripTrailing()

UTF version of trim () / trimLeft () / trimRight ()


Returns a Stream of strings for each newline


You can remove the space before and after each line by doing like.


List/Set/Map of

Returns an Immutable collection

var strs = List.of("apple", "banana");
var sets = Set.of("apple", "banana");
var dict = Map.of(
  "apple", "Apple",
  "banana", "banana");

copyOf Returns an Immutable copy

Map ofEntries() / entry()

Not only ʻof but also ʻofEntries () has been added to the Map.

var map = Map.ofEntries(
  entry("key1", "value1"),
  entry("key2", "value2"));

Predicate not

Convenient inversion of method reference

Collection toArray(IntFunction)

When converting List etc. to an array, it was necessary to prepare an array with the same size in advance, but you can generate an array like strs.toArray (String [] :: new)

Stream dropWhile / takeWhile

In Java 8, Stream processing such as "from start to end in data" was not possible, but it can be implemented by using dropWhile / takeWhile introduced in Java 9.

jshell> Stream.of("one", "start", "two", "three", "end", "four").
   ...> dropWhile(s -> !s.equals("start")).
   ...> takeWhile(s -> !s.equals("end")).
   ...> forEach(System.out::println)

In this case, it contains up to start, so you need to skip it.

jshell> Stream.of("one", "start", "two", "three", "end", "four").
   ...> dropWhile(s -> !s.equals("start")).
   ...> skip(1).
   ...> takeWhile(s -> !s.equals("end")).
   ...> forEach(System.out::println)



Iterate with two arguments has been available since Java8, but it was necessary to set a stop condition with limit etc.

IntStream.iterate(0, i -> i + 3).limit(5)

I didn't have takeWhile either, so it was quite difficult to use. And now you can use ʻiterate in combination with takeWhile`. So you can use it like a for statement.

IntStream.iterate(0, i -> i < 10, i -> i + 3)

If you write this in the following way, it will not come back. Think about why.

IntStream.iterate(0, i -> i < 10, i -> i++)

I can do this

IntStream.iterate(0, i -> i < 10, i -> ++i)

Optional/OptionalInt/OptionalLong/OptionalDouble orElseThrow() isEmpty() stream()

Converting from Optional to Stream has never been easier. This eliminates the need to insert a filter (Optional :: isPresent) when an Optional returns in a Stream. For example, if getById returns Optional

What I was doing like

ids.flatMap(id -> getById(id).stream())

You will be able to write with flatMap like this.

ifPresentOrElse or

If Optional is Empty, it is easier to write something like the following Optional.

Collectors toUnmodifiableList / toUnmodifiableSet / toUnmodifiableMap

A Collector that stores values in an immutable collection

filtering flatMapping

Enumeration asIterator

Objects requireNonNullElse requireNonNullElseGet

Path of

Files writeString

The process of writing text to a file is in one line.


The process of reading text from a file is one line.

Reader transferTo

Writing the content read by Reader as it is in Writer is one line

nullReader Writer nullWriter

InputStream transferTo

Writing the content read by InputStream as it is to OutputStream is one line


OutputStream nullOutputStream

HTTP access has been revamped.



G1GC is the default GC


CMS is deprecated

Ahead of time compilation



Launch Single-File Source-Code Programs

You can now run a single source Java code with java commands without compiling it with javac.

Module System

Java EE and CORBA is dropped

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