Java SE 12: Not Mentioned in JEP


Java SE 12 was released in 19th March!

So, I'll show updates in Java SE 12. But, I don't explain about the new features mentioned in JEPs.

In general, the updates in Java SE 12 are fewer than other Java SE releases. In the point of syntax, switch statement changes to switch expression (JEP 325). It's big change! But, the API updates are not big.


Removed APIs

There are 5 removed methods in Java SE 12.

All are the methods that forRemoval of @Deprecated set true in Java SE 10.

  • java.io.FileInputStream.finalize()
  • java.io.FileOutputStream.finalize()
  • java.util.zip.Deflater.finalize()
  • java.util.zip.Inflater.finalize()
  • java.util.zip.ZipFile.finalize()

Because these methods are only finalize methods, so you feel no difficulty for coding. If you have difficulty, the design may be wrong.


In addition, 4 methods were removed.

All of them are override getCause methods, and these classes use getCause method of super class after removing.

  • java.lang.FileNotFoundException.getCause()
  • java.lang.ExceptionInInitializerError.getCause()
  • java.lang.reflext.UndeclaredThrowableException.getCause()
  • java.security.PrivilegedActionException.getCause()


APIs proposed for Removal

There are no APIs that are added for removal in Java SE 12.


Added APIs

java.lang.constant package

A package was added to java.base module!

But, most of developer seem never to use the package. Because, the pacakge was introduced for "Condy." Cody is for dynamic constant loading as an equivalent to Indy for dynamic method invocation.

APIs included in new package are based on JEP 334: JVM Constants API.

In addition, some interfaces/class and methods are introduced in java.lang.invoke package.

Added interfaces/class are shown below:

  • TypeDescriptor interface
  • TypeDescriptor.OfField interface
  • TypeDescriptor.OfMethod interface
  • VarHandle.VarHandleDesc class

There are 3 methods added:

  • Optional<MethodHandleDesc> MethodHandle.describeConstable()
  • String MethodType.describeString()
  • Optional<MethodTypeDesc> describeConstable()

Moreover, there are 4 methods added in java.lang.Class class:

  • Class<?> arrayType()
  • Class<?> componentType()
  • Optional<ClassDesc> describeConstable()
  • String descriptorString()


Besides these, Enum class implements Constable interface, and Enum.EnumDesc inner class is added. Integer/Long/Float/Double/String classes are updated to implement ConstantDesc insterface. These classes are added describeConstant method and resolveConstantDesc method.

However, most of developers seems not to use these new condy APIs for usual software development.


java.io package

InputStream class

InputStream class has skip method, and a related method is added:

  • void skipNBytes(long n)

skip method javadoc said "The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes." For this reason, skip methods return actual number of skipping over.

Comparatively, skipNBytes method skip over and discards exactly n bytes. Because of exactly skipping over, type of skipNBytes return value is void.


java.lang package

I listed condy related updates of java.lang package, so I'll show other updates.


Character.UnicodeBloch/UnicodeScript class

Java SE 12 starts to support Unicode 11.0, but this update is not described in JEP. Java SE 11 supports Unicode 10.0.

For this update, some Unicode blocks and scripts are added. For example, CHESS_SYMBOLS that means chess pawns is added.


String class

As previously described, String class added two condy related methods. In addition, a method is added:

  • String indent(int n)

indent method inserts specified number of white spaces into head of line, and inserts new line (\n) into end of string.

jshell> var text = "Hello\nWorld!"
text ==> "Hello\nWorld!"

jshell> System.out.println(text)

jshell> text = text.indent(4)
text ==> "    Hello\n    World!\n"

jshell> System.out.println(text)


If argument is minus value, indent method removes specified number of white spaces. In this case, indent method only remove white spaces.

jshell> text = text.indent(-2)
text ==> "  Hello\n  World!\n"

jshell> text = text.indent(-3)
text ==> "Hello\nWorld!\n"


Originally, Java SE 12 planed to introduce JEP 326 Raw String Literals, but gave it up.

JEP 326 includes some String class methods definition. However, these methods were also abandoned.

Only indent method was added to String class. I don't know why.


java.net package

SecureCacheResponse class

A method to get SSL/TLS session is added to SevureCacheResponse class.

  • Optional<SSLSession> getSSLSession()


ServerSocket class

A constructe is added to ServerSocket class!

  • protected ServerSocket(SocketImpl impl)

However, this constructer is proteced method, so we don't use it in normal software development.


java.nio.file package

Files class

A method for finding mismatch points of two fiels is introduced:

  • static long mismatch(Path path, Path path2)


mismatch method finds the first difference between path and path2, and returns the position of the first difference of two.

If two files are same, mismatch method returns -1.

C:\demo>cat hello1.txt
Hello, World!

C:\demo>cat hello2.txt
Hello, Java!

C:\demo>cat hello3.txt
Hello, World!

|  Welcome to JShell -- Version 12
|  For an introduction type: /help intro

jshell> import java.nio.file.*

jshell> var hello1 = Paths.get("hello1.txt")
hello1 ==> hello1.txt

jshell> var hello2 = Paths.get("hello2.txt")
hello2 ==> hello2.txt

jshell> var hello3 = Paths.get("hello3.txt")
hello3 ==> hello3.txt

jshell> Files.mismatch(hello1, hello2)
$5 ==> 7

jshell> Files.mismatch(hello1, hello3)
$6 ==> -1



java.text package

CompactNumberFormat class

We occasionally want to show numbers using K or M like 10K (10,000). But, Java didn't have such number formatter API before.

Then, Java SE 12 introduced CompactNumberFormat class.

CompaceNumberFormat is a subclass of NumberFormat class, so usage is same. There is a constructor, but it is convenient for us to use factory methods of NumberFormat class.

jshell> import java.text.*

jshell> var formatter = NumberFormat.getCompactNumberInstance()
formatter ==> java.text.CompactNumberFormat@73cf7357

jshell> formatter.format(10000)
$3 ==> "10K"

jshell> formatter.format(12345)
$4 ==> "12K"

jshell> formatter.format(15678)
$5 ==> "16K"


The method to get CompactNumberFormat object is NumberFormat.getCompactNumberInstance method. If you use it without argument, you get CompactNumberFormat object of default locale.

In above example, the default locale is English, so the result of formatting 10,000 was 10K.

It's to be noted that default rounding is RoundingMode.HALF_UP. So, CompactNumberInstance method returns 16K when formatting 15,678.

If you'd like to use RoundingMode.FLOOR, you should use setRoundingMode method.

When formatting the number more than 1,000,000, CompactNumberFormat object uses M.

jshell> formatter.format(12_345_678)
$3 ==> "12M"


It's also to be noted that the return type of getCompactNumberInstance method is not CompactNumberFormat class but NumberFormat class.

We, Japanese count number by 104not 103. Number unit of 104 is "万" and 108 is "億".

If you'd like to use "万" or "億", you chage locale.

jshell> var formatter = NumberFormat.getCompactNumberInstance(new Locale("jp"), NumberFormat.Style.SHORT)
formatter ==> java.text.CompactNumberFormat@952071d5

jshell> formatter.format(100_000)
$5 ==> "10万"

jshell> formatter.format(123_456)
$6 ==> "12万"


Second argument type of getCompactNumberInstance method is Number.Style enum. It is introduced in Java SE 12.

There are two constants defined in Number.Style: LONG and SHORT. No argument getCompactNumberInstance method uses SHORT by default.

When locale is jp (Japanese), 100,000 is formatted to "10万" and 123,456 is formatted to "12万".


In case of LONG;

jshell> var formatter = NumberFormat.getCompactNumberInstance(new Locale("en"), NumberFormat.Style.LONG)
formatter ==> java.text.CompactNumberFormat@952071d5

jshell> formatter.format(10000)
$7 ==> "10 thousand"

jshell> formatter.format(12345)
$8 ==> "12 thousand"


"10 thousand" is compact, isn't it 🤔.


NumberFormat class

As previously explained, two static factory methods are introduced:

  • static NumberFormat getCompactNumberInstance()
  • static NumberFormat getCompactNumberInstance(Locale locale, NumberFormat.Style formatStyle)

java.text.spi.NumberFormatProvider were also added getCompactNumberInstance method.


NumberFormat.Field class

Two constants are added:

  • static final NumberFormat.Field PREFIX
  • static final NumberFormat.Field SUFFIX


NumberFormat.Style enum

Style enum is also explained previously. It is for constructing CompactNumberFormat object.

There are two constants: LONG and SHORT.


java.util.concurrent package

CompletionStage class

5 similar methods to exceptionally method are introduced.

  • default CompletionStage<T> exceptionallyAsync(Function<Throwable, ? extends T> fn)
  • default CompletionStage<T> exceptionallyAsync(Function<Throwable, ? extends T> fn, Executor executor)
  • default CompletionStage<T> exceptionallyCompose (Function<Throwable, ? extends CompletionStage<T>> fn)
  • default CompletionStage<T> exceptionallyComposeAsync(Function<Throwable, ? extends CompletionStage<T>> fn)
  • default CompletionStage<T> exceptionallyComposeAsync(Function<Throwable, ? extends CompletionStage<T>> fn, Executor executor)

exceptionally method is called when an exception is thrown in the previsou stage. If no exception in the previous stage, exceptionally method are skipped, and then next stage are executed.

exceptionallyAsync methods are called asynchronously as can be seen by method name.

jshell> import java.util.concurrent.*;
jshell> CompletableFuture.runAsync(() -> {
   ...>     System.out.println(Thread.currentThread());
   ...>     throw new RuntimeException();
   ...> }).
   ...> exceptionally(ex -> {
   ...>     System.out.println(Thread.currentThread());
   ...>     return null;
   ...> }).get();
$2 ==> null

jshell> CompletableFuture.runAsync(() -> {
   ...>     System.out.println(Thread.currentThread());
   ...>     throw new RuntimeException();
   ...> }).
   ...> exceptionallyAsync(ex -> {
   ...>     System.out.println(Thread.currentThread());
   ...>     return null;
   ...> }).get();
$3 ==> null


Executing by JShell, you can see exceptionally method is executed in main thread, but exceptionallyAsync method is executed in worker thread managed by ForkJoinPool.


The Argument of exceptionally method is a lambda expression that gets Throwable object as argument and return something value. On the other hand, the return value tyep of exceptionallyCompose method is CompletionStage class.

thenCompose method returns also CompletionStage object, so exceptionallyCompose is similar to thenCompose. As you may know, exceptionallyComposeAsync method is asynchronous version of exceptionallyCompose.


java.util.stream package

Collectors class

A method that execute two terminal operations and gathers these return values is introduced:

  • static <T,R1,R2,R> Collector<T,?,R> teeing(Collector<? super T,?,R1> downstream1, Collector<? super T,?,R2> downstream2, BiFunction<? super R1,? super R2,R> merger)

First and second argument is objects implicated Collect interface (usually we use static methods of Collectors class.) Third argument is a lambda expression for combining first and second Collect objects return values.

The following shows string concatination and couting number of characters, and then combining these two operations return values.

jshell> var text = List.of("a", "b", "c", "d", "e")
text ==> [a, b, c, d, e]

jshell> text.stream().
   ...> collect(Collectors.teeing(Collectors.joining(), 
   ...> Collectors.counting(), 
   ...> (x, y) -> x + " : " + y))
$1 ==> "abcde : 5"


It seems very useful!


javax.lang.model package

SouceVersion class

Every version up, SouceVersion add a constant:

  • static final SourceVersion RELEASE_12

On the other hand, SourceVersion class is now implementing Constable interface.



javax.naming.ldap.spi package is introduced for LDAP service provider. The package includes two class: LdapDnsProvider and LdapDnsProviderResult.

javax.net.ssl.HttpsURLConnection class is added getSSLSession method.


Swing is also added a method.

getChooserShortcutPanelFiles method is introduced in javax.swing.filechooser.FileSystemView class. But, usually we don't use the method. It is for internal use.


That's all.

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