I&#39;m trying to run DMelt programs (http://jwork.org/dmelt/) program using Java9 (JDK9), and it gives me errors such as:


    WARNING: An illegal reflective access operation has occurred
    WARNING: Illegal reflective access by org.python.core.PySystemState (file:/dmelt/jehep/lib/jython/jython.jar) to method java.io.Console.encoding()
    WARNING: Please consider reporting this to the maintainers of org.python.core.PySystemState
    WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
    WARNING: All illegal access operations will be denied in a future release

How can I fix it? I was trying to add –illegal-access=permit to the last line of the script &quot;dmelt.sh&quot; (I&#39;m using bash in Linux), but this did not solve this problem. I&#39;m very frustrating with this. I was using this program very often, for very long time. Maybe I should never move to JDK9



JDK9: An illegal reflective access operation has occurred. org.python.core.PySystemState

Let&#39;s say I have a Java project using Maven 3 and junit. There are `src/main/java` and `src/test/java` directories which contain main sources and test sources, respectively (everything is standard).

Now I want to migrate the project to Java 9. `src/main/java` content represents Java 9 module; there is `com/acme/project/module-info.java` looking approximately like this:

    module com.acme.project {
        require module1;
        require module2;
        ...
    }

What if test code needs `module-info.java` of its own? For example, to add a dependence on some module that is only needed for tests, not for production code. In such a case, I have to put `module-info.java` to `src/test/java/com/acme/project/` giving the module a different name. This way Maven seems to treat main sources and test sources as different modules, so I have to export packages from the main module to the test module, and require packages in the test module, something like this:

main module (in `src/main/java/com/acme/project`):

    module prod.module {
        exports com.acme.project to test.module;
    }

test module (in `src/test/java/com/acme/project`):

    module test.module {
        requires junit;
        requires prod.module;
    }

This produces

    [ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.7.0:testCompile (default-testCompile) on project test-java9-modules-junit: Compilation failure: Compilation failure:
    [ERROR] /home/rpuch/git/my/test-java9-modules-junit/src/test/java/com/acme/project/GreeterTest.java:[1,1] package exists in another module: prod.module

because one package is defined in two modules. So now I have to have different projects in main module and test module, which is not convenient.

I feel I follow wrong path, it all starts looking very ugly. How can I have `module-info.java` of its own in test code, or how do I achieve the same effects (`require`, etc) without it?

Java 9 + maven + junit: does test code need module-info.java of its own and where to put it?

Seems there are no 32-bit download packages on 
Oracle&#39;s available [download list](http://www.oracle.com/technetwork/java/javase/downloads/jdk9-downloads-3848520.html).

**UPDATE**

Can download here:

    wget --no-check-certificate --no-cookies --header &quot;Cookie: oraclelicense=accept-securebackup-cookie&quot; http://download.oracle.com/otn-pub/java/jdk/9+181/jdk-9_windows-x86_bin.exe


Can Java 9 run on a 32-bit OS?

Today I tried the [latest jdk9 Build 113](https://jdk9.java.net/download/) and tried to compile [my project](https://github.com/graphhopper/graphhopper/) with the latest Maven 3.3.9

These are the commands (found partially [via twitter](https://twitter.com/chriswhocodes/status/642646126689132544))

    export MVN_OPTS=&quot;-Dmaven.compiler.fork -Dmaven.compiler.executable=/somewhere/Downloads/jdk-9/bin/javac&quot;
    export JAVA_HOME=&quot;/somewhere/Downloads/jdk-9&quot;
    mvn clean install

But I get [this error](https://gist.github.com/karussell/aff591db1e46a3d2aafa12f8b4dd2f8d) ... in short:

    [WARNING] Error injecting: org.codehaus.plexus.archiver.jar.JarArchiver
    java.lang.ExceptionInInitializerError
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(java.base@9-ea/Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(java.base@9-ea/NativeConstructorAccessorImpl.java:62)

    ...

    at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
    Caused by: java.lang.ArrayIndexOutOfBoundsException: 1
        at org.codehaus.plexus.archiver.zip.AbstractZipArchiver.&lt;clinit&gt;(AbstractZipArchiver.java:116)
        ... 89 more
    [WARNING] Error injecting: org.apache.maven.plugin.jar.JarMojo
    java.lang.ExceptionInInitializerError
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(java.base@9-ea/Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(java.base@9-ea/NativeConstructorAccessorImpl.java:62)

    ...

    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
        at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
    Caused by: java.lang.ArrayIndexOutOfBoundsException: 1
        at org.codehaus.plexus.archiver.zip.AbstractZipArchiver.&lt;clinit&gt;(AbstractZipArchiver.java:116)
        ... 89 more

**What is the correct maven configuration or parameters to use for JDK9?**

    $ mvn --version
    Apache Maven 3.3.9 (bb52d8502b132ec0a5a3f4c09453c07478323dc5; 2015-11-10T17:41:47+01:00)
    Maven home: /home/somewhere/Downloads/maven
    Java version: 9-ea, vendor: Oracle Corporation
    Java home: /home/somewhere/Downloads/jdk-9
    Default locale: en_US, platform encoding: UTF-8
    OS name: &quot;linux&quot;,...


Is Maven ready for JDK9?

As an special case of https://stackoverflow.com/questions/39385658/list-of-or-collections-unmodifiablelist - what is the preferred Java 9 way of pointing to an **empty** and **immutable** list?

Keep writing

    Collections.emptyList();

or switch to

    List.of();



List.of() or Collections.emptyList()

There has been [some buzz](https://www.google.co.uk/search?q=site:mail.openjdk.java.net+sjavac) about a tool called `sjavac` on the OpenJDK mailing lists. Also, there are two related JEPs: [JEP 139: Enhance javac to Improve Build Speed](http://openjdk.java.net/jeps/139) and [JEP 199: Smart Java Compilation, Phase Two](http://openjdk.java.net/jeps/199).

My questions are:

- What exactly is the `sjavac` tool?
- Who is it intended for?
- How do I use it?

&lt;sup&gt;&lt;sub&gt;*Disclaimer: Self answered question. Just wanted to bring the knowledge of this tool to the StackOverflow community and to create a reference to future sjavac FAQ.*&lt;/sub&gt;&lt;/sup&gt;

What is sjavac, who is it for and how do I use it?

I have code and a test-case in a **legacy** application, which can be summarized as follows:

    @Test
    public void testParseDate() throws ParseException {
        String toParse = &quot;Mo Aug 18 11:25:26 MESZ +0200 2014&quot;;
        String pattern = &quot;EEE MMM dd HH:mm:ss z Z yyyy&quot;;

        DateFormat dateFormatter = new SimpleDateFormat(pattern, Locale.GERMANY);
        Date date = dateFormatter.parse(toParse);

        //skipped assumptions
    }

This test passes in Java 8 and below. However with Java 10 upwards this leads to a `java.text.ParseException: Unparseable date: &quot;Mo Aug 18 11:25:26 MESZ +0200 2014&quot;`. 

*For the record*: 
Besides `de_DE`, the exception is also thrown for the locales 
`de_CH`, `de_AT`, `de_LU`.

I am aware of the fact, that Date formatting was [changed with JDK 9][1] ([JEP 252](http://openjdk.java.net/jeps/252)). However, I consider this to be a disruptive change breaking backwards compatibility. Excerpted:

&gt;In JDK 9, the Unicode Consortium&#39;s Common Locale Data Repository (CLDR) data is enabled as the default locale data, so that you can use standard locale data without any further action.
&gt;
&gt;In JDK 8, although CLDR locale data is bundled with the JRE, it isn’t enabled by default.
&gt;
&gt;Code that uses locale-sensitive services such as date, time, and number formatting may produce different results with the CLDR locale data. 

Adding a `.` for the day of the week (`Mo.`) compensates for this and test would pass. However, this is not a real solution for old data (in serialized form such as XML).

Checking this [stackoverflow post][2], it seems that the behaviour is intentional for the German locale and can be mitigated by specifying `java.locale.providers` with `COMPAT` mode. However, I do not like the idea to rely on some system property value for two reasons as it might:

1. change in the next releases of the JDK.
2. be forgotten in different environments.

**My question is:**

- How can I maintain backwards compatibility of legacy code with this particular date pattern, without re-writing / modifying existing serialized data or adding / changing system properties (like `java.locale.providers`), which may be forgotten in different environments (application servers, standalone jars, ...) ?


  [1]: https://docs.oracle.com/javase/9/migrate/toc.htm#JSMIG-GUID-A20F2989-BFA9-482D-8618-6CBB4BAAE310
  [2]: https://stackoverflow.com/questions/46244724/jdk-dateformater-parsing-dayofweek-in-german-locale-java8-vs-java9/46245412#46245412

SimpleDateFormat with German Locale - Java 8 vs Java 10+

I have some code that uses JAXB API classes which have been provided as a part of the JDK in Java 6/7/8.  When I run the same code with Java 9, at runtime I get errors indicating that JAXB classes can not be found.

The JAXB classes have been provided as a part of the JDK since Java 6, so why can Java 9 no longer find these classes?

How to resolve java.lang.NoClassDefFoundError: javax/xml/bind/JAXBException

Java 9 [deprecated six modules that contain Java EE APIs](https://blog.codefx.org/java/java-9-migration-guide/#Dependencies-On-Java-EE-Modules) and they are [going to be removed](http://openjdk.java.net/jeps/320) soon:

* _java.activation_ with `javax.activation` package
* _java.corba_ with `javax.activity`, `javax.rmi`, `javax.rmi.CORBA`, and `org.omg.*` packages
* _java.transaction_ with `javax.transaction` package
* _java.xml.bind_ with all `javax.xml.bind.*` packages
* _java.xml.ws_ with `javax.jws`, `javax.jws.soap`, `javax.xml.soap`, and all `javax.xml.ws.*` packages
* _java.xml.ws.annotation_ with `javax.annotation` package

Which maintained third-party artifacts provide those APIs? It doesn&#39;t matter how well they provide those APIs or which other features they have to offer - all that matters is, are they a drop-in replacement for these modules/packages?

To make it easier to collect knoweldge, I answered with what I know so far and made the answer a community wiki. I hope people will extend it instead of writing their own answers.

---

Before you vote to close:

* Yes, there are already some questions on individual modules and an answer to this question would of course duplicate that information. But AFAIK there is no single point to learn about all of these, which I think has a lot of value.
* Questions asking for library recommendations are usually considered off-topic, because &quot;they tend to attract opinionated answers and spam&quot;, but I don&#39;t think that applies here. The set of valid libraries is clearly delineated: They have to implement a specific standard. Beyond that nothing else matters, so I don&#39;t see much risk for opinion and spam.


Replacements for deprecated JPMS modules with Java EE APIs

Java 9 introduced new factory methods for lists, [`List.of`](https://docs.oracle.com/javase/9/docs/api/java/util/List.html#of-E...-):

    List&lt;String&gt; strings = List.of(&quot;first&quot;, &quot;second&quot;);

What&#39;s the difference between the previous and the new option? That is, what&#39;s the difference between this:

    Arrays.asList(1, 2, 3);

and this:

    List.of(1, 2, 3);


What is the difference between List.of and Arrays.asList?

There are a lot of questions about illegal reflective access in Java 9.

I have found plenty of discussion about working around the error messages, but I would love to know what an illegal reflective access actually is.

So my question is:  

What defines an illegal reflective access and what circumstances trigger the warning?

I have gathered that it has something to do with the encapsulation principles that were introduced in Java 9, but I can&#39;t find an explanation of how it all hangs together, what triggers the warning, and in what scenario.

What is an illegal reflective access?

For a challenge, [a fellow code golfer](https://stackoverflow.com/users/1682559/kevin-cruijssen) [wrote the following code](https://codegolf.stackexchange.com/questions/166012/exchange-capitalization/166081?noredirect=1#comment401670_166081):

    import java.util.*;
    public class Main {
      public static void main(String[] args) {
        int size = 3;
        String[] array = new String[size];
        Arrays.fill(array, &quot;&quot;);
        for (int i = 0; i &lt;= 100;) {
          array[i++ % size] += i + &quot; &quot;;
        }
        for (String element: array) {
          System.out.println(element);
        }
      }
    }

[When running this code in Java 8, we get the following result:](https://tio.run/##TY3BTsMwEETv@YpRJKSEgFXEjZADH8CpxyoH07rVps46sjdFFcq3BzduKafdnXkz2@mTfnaD4W53nGfqB@cFXRTVKGTVY51lw/hlaYut1SHgUxPjJwOuahAtcZwc7dBHr1iLJz5sWmh/COWCAsQCRoPXejn/MV6fo87m@yZym5iPixXUnqwtFuwJeV4mb@98camkGF3Vcbw3eFnF7fYPqXlDVfXALaomMhVy5Ck//bWkpzDW9IblLcXuLetzENMrN4oaIiiWiyta3pumbJrnXw)

    1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76 79 82 85 88 91 94 97 100 
    2 5 8 11 14 17 20 23 26 29 32 35 38 41 44 47 50 53 56 59 62 65 68 71 74 77 80 83 86 89 92 95 98 101 
    3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69 72 75 78 81 84 87 90 93 96 99 

[When running this code in Java 10, we get the following result:](https://tio.run/##TY3NboMwEITvPMUIqRKU1krUWymHPkBPOUYcnMSJlpgF2UuqqOLZiYPz09Puznwz2@iTfm92x2mitu@coAmCGoSsei2TpB82lrbYWu09fjQx/hLgpnrREsapox3a4GUrccSHdQ3tDj6fUYBYwKjwUc7nP8bpc9DZ/N5FriPzfbW82pO12Yy9IU3z6O07l10rKUQXZRhfFZaLsN3/ITavqSheuEZRBaZAijTmx0dLfApjTWtYPmPs2bI6ezGt6gZRfQDFcnZD82fTmIzTdAE)

    2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 
    2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 100 102 
    2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 100 

The numbering is entirely off using Java 10. So what is happening here? Is it a bug in Java 10?

## Follow ups from the comments:

* The issue appears when compiled with Java 9 or later (we found it in Java 10). Compiling this code on Java 8, then running in Java 9 or any later version, including Java 11 early access, gives the expected result.
* This kind of code is non-standard, but is valid according to the spec. It was found by [Kevin Cruijssen](https://stackoverflow.com/users/1682559/kevin-cruijssen) in a [discussion in a **golfing challenge**](https://codegolf.stackexchange.com/questions/166012/exchange-capitalization/166081?noredirect=1#comment401670_166081), hence the weird use case encountered.
* [Didier L](https://stackoverflow.com/users/525036/didier-l) simplified the issue with this much smaller and more understandable code:
     
        class Main {
          public static void main(String[] args) {
            String[] array = { &quot;&quot; };
            array[test()] += &quot;a&quot;;
          }
          static int test() {
            System.out.println(&quot;evaluated&quot;);
            return 0;
          }
        }

   [Result when compiled in Java 8:](https://tio.run/##TYxBCoMwFET3PcWQVaRUui8eoasuxcWvBomNUZIfQcSzp6lpoYthYN7wBlroMs3KDt0rxtaQ97iTtthOwByeRrfwTJxqmXSHMTH5YKdtXzcg1/viuAJ/o6MVFTYIgf12wGOrWXmWRYNzBUHiQ/aUr15bRj78hKtnNZZT4HJOajZWCrWQCcSqE0UWO8XBWVyzbI/xDQ)

        evaluated

   [Result when compiled in Java 9 and 10:](https://tio.run/##TYxBCoMwFET3PcWQlaFUui8eoasuxcWvBomNUZIfQcSzp6lpoYthYN7wBlroMnSvGFtD3uNO2mI7AXN4Gt3CM3GqZdIdxsSKBztt@7oBud7L4wr8jY5WVNggBPbbAY@tZuW5kA3OFQSJD9lTvnptGfnwE66e1VhOgcs5qdnYQqiFTCBWnZBZ7BQHZ3HNsj3GNw)

        evaluated
        evaluated

* The issue seems to be limited to the string concatenation and assignment operator (`+=`) with an expression with side effect(s) as the left operand, like in `array[test()]+=&quot;a&quot;`, `array[ix++]+=&quot;a&quot;`, `test()[index]+=&quot;a&quot;`, or `test().field+=&quot;a&quot;`. To enable string concatenation, at least one of the sides must have type `String`. Trying to reproduce this on other types or constructs failed.


Why does array[idx++]+=&quot;a&quot; increase idx once in Java 8 but twice in Java 9 and 10?

Java 9 came out, and [`Observer`](https://docs.oracle.com/javase/9/docs/api/java/util/Observer.html) has been deprecated.
Why is that? Does it mean that we shouldn&#39;t implement observer pattern anymore? 

It would be good to know what is a better alternative?

Observer is deprecated in Java 9. What should we use instead of it?

I&#39;ve been working with the new [Optional type in Java 8](https://docs.oracle.com/javase/8/docs/api/java/util/Optional.html), and I&#39;ve come across what seems like a common operation that isn&#39;t supported functionally: an &quot;orElseOptional&quot;

Consider the following pattern:

    Optional&lt;Result&gt; resultFromServiceA = serviceA(args);
    if (resultFromServiceA.isPresent) return result;
    else {
        Optional&lt;Result&gt; resultFromServiceB = serviceB(args);
        if (resultFromServiceB.isPresent) return resultFromServiceB;
        else return serviceC(args);
    }

There are many forms of this pattern, but it boils down to wanting an &quot;orElse&quot; on an optional that takes a function producing a new optional, called only if the current one does not exist.

It&#39;s implementation would look like this:

    public Optional&lt;T&gt; orElse(Supplier&lt;Optional&lt;? extends T&gt;&gt; otherSupplier) {
        return value != null ? this : other.get();
    }

I&#39;m curious if there&#39;s a reason such a method doesn&#39;t exist, if I&#39;m just using Optional in an unintended way, and what other ways people have come up with to deal with this case.

I should say that I think that solutions involving custom utility classes/methods aren&#39;t elegant because people working with my code won&#39;t necessarily know they exist.

Also, if anyone knows, will such a method be included in JDK 9, and where might I propose such a method? This seems like a pretty glaring omission to the API to me.

Optional orElse Optional in Java

This exception occurs in a wide variety of scenarios when running an application on Java 9.
Certain libraries and frameworks (Spring, Hibernate, JAXB) are particularly prone to it.
Here&#39;s an example from Javassist:

    java.lang.reflect.InaccessibleObjectException: Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain) throws java.lang.ClassFormatError accessible: module java.base does not &quot;opens java.lang&quot; to unnamed module @1941a8ff
        at java.base/jdk.internal.reflect.Reflection.throwInaccessibleObjectException(Reflection.java:427)
        at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:201)
        at java.base/java.lang.reflect.Method.checkCanSetAccessible(Method.java:192)
        at java.base/java.lang.reflect.Method.setAccessible(Method.java:186)
        at javassist.util.proxy.SecurityActions.setAccessible(SecurityActions.java:102)
        at javassist.util.proxy.FactoryHelper.toClass2(FactoryHelper.java:180)
        at javassist.util.proxy.FactoryHelper.toClass(FactoryHelper.java:163)
        at javassist.util.proxy.ProxyFactory.createClass3(ProxyFactory.java:501)
        at javassist.util.proxy.ProxyFactory.createClass2(ProxyFactory.java:486)
        at javassist.util.proxy.ProxyFactory.createClass1(ProxyFactory.java:422)
        at javassist.util.proxy.ProxyFactory.createClass(ProxyFactory.java:394)

The message says:

&gt;  Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain) throws java.lang.ClassFormatError accessible: module java.base does not &quot;opens java.lang&quot; to unnamed module @1941a8ff

What can be done to avoid the exception and have the program run successfully?


How to solve InaccessibleObjectException (&quot;Unable to make {member} accessible: module {A} does not &#39;opens {package}&#39; to {B}&quot;) on Java 9?

Java 9&#39;s `javac` has a new flag `--release`:

    &gt; javac --help
    ...

    --release &lt;release&gt;
        Compile for a specific VM version. Supported targets: 6, 7, 8, 9

How is it different from `-source` and `-target` flags? Is it just a shortcut for `-source X -target X`?

What is the --release flag in the Java 9 compiler?

I downloaded and installed:

- JDK (`jdk-9.0.1_osx-x64_bin.dmg`) from Oracle [here](http://www.oracle.com/technetwork/java/javase/downloads/index.html)
- Android SDK (`sdk-tools-darwin-3859397.zip`) from Google [here](https://developer.android.com/studio/index.html).

After configuring the `PATH` variable, I tried running `sdkmanager`, which replaced the `android` command for managing SDK components. However, it failed as shown here:

    $ sdkmanager --list
    Exception in thread &quot;main&quot; java.lang.NoClassDefFoundError: javax/xml/bind/annotation/XmlSchema
    	at com.android.repository.api.SchemaModule$SchemaModuleVersion.&lt;init&gt;(SchemaModule.java:156)
    	at com.android.repository.api.SchemaModule.&lt;init&gt;(SchemaModule.java:75)
    	at com.android.sdklib.repository.AndroidSdkHandler.&lt;clinit&gt;(AndroidSdkHandler.java:81)
    	at com.android.sdklib.tool.SdkManagerCli.main(SdkManagerCli.java:117)
    	at com.android.sdklib.tool.SdkManagerCli.main(SdkManagerCli.java:93)
    Caused by: java.lang.ClassNotFoundException: javax.xml.bind.annotation.XmlSchema
    	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:582)
    	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:185)
    	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:496)
    	... 5 more

Here is the Java version:

    $ java -version
    java version &quot;9.0.1&quot;
    Java(TM) SE Runtime Environment (build 9.0.1+11)
    Java HotSpot(TM) 64-Bit Server VM (build 9.0.1+11, mixed mode)

Does anyone know how to fix it without going back to Java 8?

# Related Questions

- https://stackoverflow.com/q/46402772/142239
  - This post asked a similar question. However, the post is closed and the only answer suggests going back to Java 8.

# WARNING

Please note that I already mentioned above that going back to **Java 8** or running it side-by-side is **NOT** what I wanted.

Failed to run sdkmanager --list with Java 9

As written in [*JEP 280: Indify String Concatenation*][1]:

&gt;Change the static `String`-concatenation bytecode sequence generated by `javac` to use `invokedynamic` calls to JDK library functions. This will enable future optimizations of `String` concatenation without requiring further changes to the bytecode emmited by `javac`.

Here I want to understand what the use of `invokedynamic` calls is and how bytecode concatenation is different from `invokedynamic`?

  [1]: http://openjdk.java.net/jeps/280

How is String concatenation implemented in Java 9?

With Java 9, new factory methods have been introduced for the `List`, `Set` and `Map` interfaces. These methods allow quickly instantiating a Map object with values in one line. Now, if we consider: 

    Map&lt;Integer, String&gt; map1 = new HashMap&lt;Integer, String&gt;(Map.of(1, &quot;value1&quot;, 2, &quot;value2&quot;, 3, &quot;value3&quot;));
    map1.put(4, null);

The above is allowed without any exception while if we do:

    Map&lt;Integer, String&gt; map2 = Map.of(1, &quot;value1&quot;, 2, &quot;value2&quot;, 3, &quot;value3&quot;, 4, null );

It throws:

    Exception in thread &quot;main&quot; java.lang.NullPointerException
        at java.base/java.util.Objects.requireNonNull(Objects.java:221)
    ..
I am not able to get, **why null is not allowed** in second case. 

I know HashMap can take null as a key as well as a value but why was that restricted in the case of Map.of? 

The same thing happens in the case of `java.util.Set.of(&quot;v1&quot;, &quot;v2&quot;, null)` and `java.util.List.of(&quot;v1&quot;, &quot;v2&quot;, null)`.

Why does Map.of not allow null keys and values?

I&#39;m trying to run my Spring Boot application on Java 9, and I&#39;ve faced with JAXB problem, which described in the guides, but didn&#39;t work for me. I&#39;ve added dependency on JAXB api, and application started working.
If you get the following exception, as a result of missing JAXB missing implementation using Java version &gt;=9:

    javax.xml.bind.JAXBException: Implementation of JAXB-API has not been found on module path or classpath.
    	at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:177) ~[jaxb-api-2.3.0.jar:2.3.0]
    	at javax.xml.bind.ContextFinder.find(ContextFinder.java:364) ~[jaxb-api-2.3.0.jar:2.3.0]
    	at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:508) ~[jaxb-api-2.3.0.jar:2.3.0]
    	at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:465) ~[jaxb-api-2.3.0.jar:2.3.0]
    	at javax.xml.bind.JAXBContext.newInstance(JAXBContext.java:366) ~[jaxb-api-2.3.0.jar:2.3.0]
    	at com.sun.jersey.server.impl.wadl.WadlApplicationContextImpl.&lt;init&gt;(WadlApplicationContextImpl.java:107) ~[jersey-server-1.19.1.jar:1.19.1]
    	at com.sun.jersey.server.impl.wadl.WadlFactory.init(WadlFactory.java:100) [jersey-server-1.19.1.jar:1.19.1]
    	at com.sun.jersey.server.impl.application.RootResourceUriRules.initWadl(RootResourceUriRules.java:169) [jersey-server-1.19.1.jar:1.19.1]
    	at com.sun.jersey.server.impl.application.RootResourceUriRules.&lt;init&gt;(RootResourceUriRules.java:106) [jersey-server-1.19.1.jar:1.19.1]
    	at com.sun.jersey.server.impl.application.WebApplicationImpl._initiate(WebApplicationImpl.java:1359) [jersey-server-1.19.1.jar:1.19.1]
    	at com.sun.jersey.server.impl.application.WebApplicationImpl.access$700(WebApplicationImpl.java:180) [jersey-server-1.19.1.jar:1.19.1]
    	at com.sun.jersey.server.impl.application.WebApplicationImpl$13.f(WebApplicationImpl.java:799) [jersey-server-1.19.1.jar:1.19.1]
    	at com.sun.jersey.server.impl.application.WebApplicationImpl$13.f(WebApplicationImpl.java:795) [jersey-server-1.19.1.jar:1.19.1]
    	at com.sun.jersey.spi.inject.Errors.processWithErrors(Errors.java:193) [jersey-core-1.19.1.jar:1.19.1]
    	at com.sun.jersey.server.impl.application.WebApplicationImpl.initiate(WebApplicationImpl.java:795) [jersey-server-1.19.1.jar:1.19.1]
    	at com.sun.jersey.server.impl.application.WebApplicationImpl.initiate(WebApplicationImpl.java:790) [jersey-server-1.19.1.jar:1.19.1]
    	at com.sun.jersey.spi.container.servlet.ServletContainer.initiate(ServletContainer.java:509) [jersey-servlet-1.19.1.jar:1.19.1]
    	at com.sun.jersey.spi.container.servlet.ServletContainer$InternalWebComponent.initiate(ServletContainer.java:339) [jersey-servlet-1.19.1.jar:1.19.1]
    	at com.sun.jersey.spi.container.servlet.WebComponent.load(WebComponent.java:605) [jersey-servlet-1.19.1.jar:1.19.1]
    	at com.sun.jersey.spi.container.servlet.WebComponent.init(WebComponent.java:207) [jersey-servlet-1.19.1.jar:1.19.1]
    	at com.sun.jersey.spi.container.servlet.ServletContainer.init(ServletContainer.java:394) [jersey-servlet-1.19.1.jar:1.19.1]
    	at com.sun.jersey.spi.container.servlet.ServletContainer.init(ServletContainer.java:744) [jersey-servlet-1.19.1.jar:1.19.1]
    	at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:270) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.core.ApplicationFilterConfig.&lt;init&gt;(ApplicationFilterConfig.java:106) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4491) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5135) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1427) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1417) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) [na:na]
    	at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at java.base/java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:140) [na:na]
    	at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:943) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:839) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1427) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1417) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) [na:na]
    	at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at java.base/java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:140) [na:na]
    	at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:943) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:258) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.core.StandardService.startInternal(StandardService.java:422) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:770) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.apache.catalina.startup.Tomcat.start(Tomcat.java:371) [tomcat-embed-core-9.0.10.jar:9.0.10]
    	at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.initialize(TomcatWebServer.java:107) [spring-boot-2.1.0.M1.jar:2.1.0.M1]
    	at org.springframework.boot.web.embedded.tomcat.TomcatWebServer.&lt;init&gt;(TomcatWebServer.java:86) [spring-boot-2.1.0.M1.jar:2.1.0.M1]
    	at org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory.getTomcatWebServer(TomcatServletWebServerFactory.java:413) [spring-boot-2.1.0.M1.jar:2.1.0.M1]
    	at org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory.getWebServer(TomcatServletWebServerFactory.java:174) [spring-boot-2.1.0.M1.jar:2.1.0.M1]
    	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.createWebServer(ServletWebServerApplicationContext.java:179) [spring-boot-2.1.0.M1.jar:2.1.0.M1]
    	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:152) [spring-boot-2.1.0.M1.jar:2.1.0.M1]
    	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:542) [spring-context-5.1.0.RC1.jar:5.1.0.RC1]
    	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) [spring-boot-2.1.0.M1.jar:2.1.0.M1]
    	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:769) [spring-boot-2.1.0.M1.jar:2.1.0.M1]
    	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:405) [spring-boot-2.1.0.M1.jar:2.1.0.M1]
    	at org.springframework.boot.SpringApplication.run(SpringApplication.java:334) [spring-boot-2.1.0.M1.jar:2.1.0.M1]
    	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1252) [spring-boot-2.1.0.M1.jar:2.1.0.M1]
    	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1240) [spring-boot-2.1.0.M1.jar:2.1.0.M1]
    	at io.eureka.server.EurekaServerApp.main(EurekaServerApp.java:21) [classes/:na]
    	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    	at java.base/java.lang.reflect.Method.invoke(Method.java:564) ~[na:na]
    	at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) [spring-boot-devtools-2.1.0.M1.jar:2.1.0.M1]
    Caused by: java.lang.ClassNotFoundException: com.sun.xml.internal.bind.v2.ContextFactory
    	at org.springframework.boot.web.embedded.tomcat.TomcatEmbeddedWebappClassLoader.loadClass(TomcatEmbeddedWebappClassLoader.java:70) ~[spring-boot-2.1.0.M1.jar:2.1.0.M1]
    	at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1138) ~[tomcat-embed-core-9.0.10.jar:9.0.10]
    	at javax.xml.bind.ServiceLoaderUtil.nullSafeLoadClass(ServiceLoaderUtil.java:122) ~[jaxb-api-2.3.0.jar:2.3.0]
    	at javax.xml.bind.ServiceLoaderUtil.safeLoadClass(ServiceLoaderUtil.java:155) ~[jaxb-api-2.3.0.jar:2.3.0]
    	at javax.xml.bind.ContextFinder.newInstance(ContextFinder.java:174) ~[jaxb-api-2.3.0.jar:2.3.0]
    	... 66 common frames omitted



javax.xml.bind.JAXBException Implementation of JAXB-API has not been found on module path or classpath

When using the JShell, how do I exit it back to the CMD line?

I have already tried &lt;kbd&gt;ctrl&lt;/kbd&gt; + &lt;kbd&gt;x&lt;/kbd&gt; and just writing quit, but to no joy.

How to quit the JShell and go back to the command-line?

What&#39;s the difference between ***requires*** and ***requires transitive*** module statements in module declaration?&lt;br&gt;&lt;br&gt;
For example:

    module foo {
        requires java.base;
        requires transitive java.compiler;
    }

What&#39;s the difference between requires and requires transitive statements in Java 9?

Trying to compile a Maven project using JDK 9.0.1 I&#39;m facing this stacktrace without much of an explanation:

    Exception in thread &quot;main&quot; java.lang.AssertionError
    at jdk.compiler/com.sun.tools.javac.util.Assert.error(Assert.java:155)
    at jdk.compiler/com.sun.tools.javac.util.Assert.check(Assert.java:46)
    at jdk.compiler/com.sun.tools.javac.comp.Modules.enter(Modules.java:250)
    at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.readSourceFile(JavaCompiler.java:821)
    at jdk.compiler/com.sun.tools.javac.processing.JavacProcessingEnvironment$ImplicitCompleter.complete(JavacProcessingEnvironment.java:1510)
    at jdk.compiler/com.sun.tools.javac.code.Symbol.complete(Symbol.java:633)
    at jdk.compiler/com.sun.tools.javac.code.Symbol$ClassSymbol.complete(Symbol.java:1314)
    at jdk.compiler/com.sun.tools.javac.code.Type$ClassType.complete(Type.java:1139)
    at jdk.compiler/com.sun.tools.javac.code.Type$ClassType.getTypeArguments(Type.java:1065)
    at jdk.compiler/com.sun.tools.javac.code.Printer.visitClassType(Printer.java:237)
    at jdk.compiler/com.sun.tools.javac.code.Printer.visitClassType(Printer.java:52)
    at jdk.compiler/com.sun.tools.javac.code.Type$ClassType.accept(Type.java:992)
    at jdk.compiler/com.sun.tools.javac.code.Printer.visit(Printer.java:136)
    at jdk.compiler/com.sun.tools.javac.util.AbstractDiagnosticFormatter.formatArgument(AbstractDiagnosticFormatter.java:197)
    at jdk.compiler/com.sun.tools.javac.util.AbstractDiagnosticFormatter.formatArguments(AbstractDiagnosticFormatter.java:165)
    at jdk.compiler/com.sun.tools.javac.util.BasicDiagnosticFormatter.formatMessage(BasicDiagnosticFormatter.java:111)
    at jdk.compiler/com.sun.tools.javac.util.BasicDiagnosticFormatter.formatMessage(BasicDiagnosticFormatter.java:67)
    at jdk.compiler/com.sun.tools.javac.util.AbstractDiagnosticFormatter.formatArgument(AbstractDiagnosticFormatter.java:183)
    at jdk.compiler/com.sun.tools.javac.util.AbstractDiagnosticFormatter.formatArguments(AbstractDiagnosticFormatter.java:165)
    at jdk.compiler/com.sun.tools.javac.util.BasicDiagnosticFormatter.formatMessage(BasicDiagnosticFormatter.java:111)
    at jdk.compiler/com.sun.tools.javac.util.BasicDiagnosticFormatter.formatMessage(BasicDiagnosticFormatter.java:67)
    at jdk.compiler/com.sun.tools.javac.util.JCDiagnostic.getMessage(JCDiagnostic.java:771)
    at jdk.compiler/com.sun.tools.javac.api.ClientCodeWrapper$DiagnosticSourceUnwrapper.getMessage(ClientCodeWrapper.java:799)
    at org.codehaus.plexus.compiler.javac.JavaxToolsCompiler.compileInProcess(JavaxToolsCompiler.java:131)
    at org.codehaus.plexus.compiler.javac.JavacCompiler.performCompile(JavacCompiler.java:174)
    at org.apache.maven.plugin.compiler.AbstractCompilerMojo.execute(AbstractCompilerMojo.java:1075)
    at org.apache.maven.plugin.compiler.CompilerMojo.execute(CompilerMojo.java:168)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:154)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:146)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:309)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:194)
    at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:107)
    at org.apache.maven.cli.MavenCli.execute(MavenCli.java:993)
    at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:345)
    at org.apache.maven.cli.MavenCli.main(MavenCli.java:191)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:564)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)

Not really sure what&#39;s causing this, is this a bug in the JDK?

***Additional details***:

* Maven 3.5.0 with maven-compiler-plugin 3.7.0
* I&#39;m just executing mvn clean install
* The source code is not open source unfortunately, so I&#39;m not at liberty to share it
* There are no module-info.java files yet, I&#39;m just trying to compile a project using Java 9
* Strangely enough if I leave the source level on 1.8, the code compiles, but it fails with the above exception if I specify it as 9

Maven compilation issue with Java 9

I just tried to run my server with Java 9 and got next warning:


    WARNING: An illegal reflective access operation has occurred
    WARNING: Illegal reflective access by io.netty.util.internal.ReflectionUtil (file:/home/azureuser/server-0.28.0-SNAPSHOT.jar) to constructor java.nio.DirectByteBuffer(long,int)
    WARNING: Please consider reporting this to the maintainers of io.netty.util.internal.ReflectionUtil
    WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
    WARNING: All illegal access operations will be denied in a future release

I would like to hide this warning without adding `--illegal-access=deny` to JVM options during start. Something like:

    System.setProperty(&quot;illegal-access&quot;, &quot;deny&quot;);

Is there any way to do that?

All related answers suggesting to use JVM options, I would like to turn off this from code. Is that possible?

To clarify - my question is about turning this warning from the code and not via JVM arguments/flags as stated in similar questions.

How to hide warning &quot;Illegal reflective access&quot; in java 9 without JVM argument?

I&#39;m trying to create a bean from sources that were generated by [`wsdl2java`](https://github.com/nilsmagnus/wsdl2java).

Every time I try to run my Spring Boot app, I get the following error:

&gt; Caused by: java.lang.ClassCastException: class
&gt; org.apache.cxf.endpoint.ClientImpl cannot be cast to class
&gt; com.xignite.services.XigniteCurrenciesSoap
&gt; (org.apache.cxf.endpoint.ClientImpl and
&gt; com.xignite.services.XigniteCurrenciesSoap are in unnamed module of
&gt; loader &#39;app&#39;)

I&#39;m not sure how exactly I&#39;m to include generated sources in my main Spring Boot application as a module.

My directory structure is:

    ├── build
    │&#160;&#160; └── generatedsources
    │       └── src
    │           └── main
    │               └── java
    │                   └── com
    │                       └── xignite
    │                           └── services
    │      
    └── src
        └── main
            ├── java
            │&#160;&#160; └── io
            │&#160;&#160;     └── mateo
            │&#160;&#160;         └── stackoverflow
            │&#160;&#160;             └── soapconsumption
            └── resources
        &#160;&#160;     └── wsdls

Relevant system info:

    openjdk version &quot;11.0.1&quot; 2018-10-16
    OpenJDK Runtime Environment 18.9 (build 11.0.1+13)
    OpenJDK 64-Bit Server VM 18.9 (build 11.0.1+13, mixed mode)

* Spring Boot 2.1.2.RELEASE
* Gradle 5.2

I&#39;ve also uploaded the project onto Github here: https://github.com/ciscoo/soap-consumption-spring-boot

Cannot be cast to class because they are in unnamed module of loader &#39;app&#39;

When installing the android sdk tools the following error is emitted:
&gt;java.lang.NoClassDefFoundError: javax/xml/bind/annotation/XmlSchema

Why is this happening and how can it be fixed?

Debug output:

    $ java --version
    java 9
    Java(TM) SE Runtime Environment (build 9+181)
    Java HotSpot(TM) 64-Bit Server VM (build 9+181, mixed mode)
    $ brew cask install android-sdk
    ==&gt; Caveats
    We will install android-sdk-tools, platform-tools, and build-tools for you.
    You can control android sdk packages via the sdkmanager command.
    You may want to add to your profile:
      &#39;export ANDROID_SDK_ROOT=/usr/local/share/android-sdk&#39;
    
    This operation may take up to 10 minutes depending on your internet connection.
    Please, be patient.
    
    ==&gt; Satisfying dependencies
    ==&gt; Downloading https://dl.google.com/android/repository/sdk-tools-darwin-3859397.zip
    Already downloaded: /Users/tomasnovella/Library/Caches/Homebrew/Cask/android-sdk--3859397,26.0.1.zip
    ==&gt; Verifying checksum for Cask android-sdk
    ==&gt; Installing Cask android-sdk
    ==&gt; Exception in thread &quot;main&quot;
    ==&gt; java.lang.NoClassDefFoundError: javax/xml/bind/annotation/XmlSchema
    ==&gt; 	at com.android.repository.api.SchemaModule$SchemaModuleVersion.&lt;init&gt;(SchemaModule.java:156)
    ==&gt; 	at com.android.repository.api.SchemaModule.&lt;init&gt;(SchemaModule.java:75)
    ==&gt; 	at com.android.sdklib.repository.AndroidSdkHandler.&lt;clinit&gt;(AndroidSdkHandler.java:81)
    ==&gt; 	at com.android.sdklib.tool.SdkManagerCli.main(SdkManagerCli.java:117)
    ==&gt; 	at com.android.sdklib.tool.SdkManagerCli.main(SdkManagerCli.java:93)
    ==&gt; Caused by: java.lang.ClassNotFoundException: javax.xml.bind.annotation.XmlSchema
    ==&gt; 	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:582)
    ==&gt; 	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:185)
    ==&gt; 	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:496)
    ==&gt; 	... 5 more
    Error: Command failed to execute!
    
    ==&gt; Failed command:
    /usr/local/Caskroom/android-sdk/3859397,26.0.1/tools/bin/sdkmanager tools platform-tools build-tools;26.0.1
    
    ==&gt; Standard Output of failed command:
    
    
    ==&gt; Standard Error of failed command:
    Exception in thread &quot;main&quot; java.lang.NoClassDefFoundError: javax/xml/bind/annotation/XmlSchema
    	at com.android.repository.api.SchemaModule$SchemaModuleVersion.&lt;init&gt;(SchemaModule.java:156)
    	at com.android.repository.api.SchemaModule.&lt;init&gt;(SchemaModule.java:75)
    	at com.android.sdklib.repository.AndroidSdkHandler.&lt;clinit&gt;(AndroidSdkHandler.java:81)
    	at com.android.sdklib.tool.SdkManagerCli.main(SdkManagerCli.java:117)


Failed to install android-sdk: &quot;java.lang.NoClassDefFoundError: javax/xml/bind/annotation/XmlSchema&quot;

Java&#39;s package management system always seemed simple and effective to me. It is heavily used by the JDK itself. We have been using it to mimic the concept of namespaces and modules.

What is **Project Jigsaw** (aka [Java Platform Module System][1]) trying to fill in?

From the official site:

&gt; The goal of this Project is to design and implement a standard module
&gt; system for the Java SE Platform, and to apply that system to the
&gt; Platform itself and to the JDK.


  [1]: https://jcp.org/en/jsr/detail?id=376

Why project Jigsaw / JPMS?

The following code compiles in both Java 8 &amp; 9, but behaves differently.

&lt;!-- language: lang-java --&gt;

    class Simple {
        static String sample = &quot;\nEn un lugar\r\nde la Mancha\nde cuyo nombre\r\nno quiero acordarme&quot;;
    
        public static void main(String args[]){
            String[] chunks = sample.split(&quot;\\R\\R&quot;);
            for (String chunk: chunks) {
                System.out.println(&quot;Chunk : &quot;+chunk);
            }
        }
    }


When I run it with Java 8 it returns:

&lt;!-- language: lang-none --&gt;

    Chunk : 
    En un lugar
    de la Mancha
    de cuyo nombre
    no quiero acordarme


But when I run it with Java 9 the output is different:

&lt;!-- language: lang-none --&gt;

    Chunk : 
    En un lugar
    Chunk : de la Mancha
    de cuyo nombre
    Chunk : no quiero acordarme

Why?

Why does \R behave differently in regular expressions between Java 8 and Java 9?

Seems like `javax.activation` package is deprecated in Java 9.
Oracle migration guide proposes to use `--add-modules java.activation` option during JVM start. 

However, I would like to avoid this and replace `javax.activation` package&#39;s classes, as it is deprecated and will be removed in future java versions. I suppose, there should be some kind of alternative for `javax.activation`. If there is any available, what is it?



What is the replacement for javax.activation package in java 9?

I am creating snippets with takeWhile to explore its possibilities. When used in conjunction with flatMap, the behaviour is not in line with the expectation. Please find the code snippet below.

    String[][] strArray = {{&quot;Sample1&quot;, &quot;Sample2&quot;}, {&quot;Sample3&quot;, &quot;Sample4&quot;, &quot;Sample5&quot;}};

    Arrays.stream(strArray)
            .flatMap(indStream -&gt; Arrays.stream(indStream))
            .takeWhile(ele -&gt; !ele.equalsIgnoreCase(&quot;Sample4&quot;))
            .forEach(ele -&gt; System.out.println(ele));

Actual Output:

    Sample1
    Sample2
    Sample3
    Sample5

ExpectedOutput:

    Sample1
    Sample2
    Sample3

Reason for the expectation is that takeWhile should be executing till the time the condition inside turns true. I have also added printout statements inside flatmap for debugging. The streams are returned just twice which is inline with the expectation.

However, this works just fine without flatmap in the chain.

    String[] strArraySingle = {&quot;Sample3&quot;, &quot;Sample4&quot;, &quot;Sample5&quot;};
    Arrays.stream(strArraySingle)
            .takeWhile(ele -&gt; !ele.equalsIgnoreCase(&quot;Sample4&quot;))
            .forEach(ele -&gt; System.out.println(ele));

Actual Output:

    Sample3

Here the actual output matches with the expected output. 

Disclaimer: These snippets are just for code practise and does not serve any valid usecases.

**Update:** 
Bug [JDK-8193856][1]: fix will be available as part of JDK 10.
The change will be to correct `whileOps`
Sink::accept


    @Override 
    public void accept(T t) {
        if (take = predicate.test(t)) {
            downstream.accept(t);
        }
    }

Changed Implementation:

    @Override
    public void accept(T t) {
        if (take &amp;&amp; (take = predicate.test(t))) {
            downstream.accept(t);
        }
    }


  [1]: https://bugs.openjdk.java.net/browse/JDK-8193856

takeWhile() working differently with flatmap

Java 9 has three ways to package compiled code in files:

 - JAR
 - JMOD
 - JIMAGE 

JIMAGE is optimized for speed and space and used by the JVM at runtime so it makes sense why JIMAGE was introduced. JIMAGE files are not supposed to be published to maven repos or used at compile or link time. 

The docs claim that JMOD can store native code and other things that can&#39;t be stored by JAR files and that developers can make and distribute their own JMOD files. The JDK ships with `jmods/` directory containing all the modules of the JDK for users to depend on. 

**Questions:** 

 - Why did Java 9 introduce the JMOD file format?
 - Should a library author distribute a JMOD file or a JAR file or both? 
 - Should jmod files be published to maven repos? 



Why did Java 9 introduce the JMOD file format?

I am in the progress of learning through Java 8 lambda expressions and would like to ask about the following piece of Java code relating to the [`peek`][peek] method in the function interface that I have come across.

On execution of the program on IDE, it gives no output. I was expecting it would give `2, 4, 6`.

    import java.util.Arrays;
    import java.util.List;
    
    public class Test_Q3 {

	    public Test_Q3() {
	    }

	    public static void main(String[] args) {
            List&lt;Integer&gt; values = Arrays.asList(1, 2, 3);
		    values.stream()
		          .map(n -&gt; n * 2)
		          .peek(System.out::print)
		          .count();
	    }
    }

[peek]: https://docs.oracle.com/javase/9/docs/api/java/util/stream/Stream.html#peek-java.util.function.Consumer-


Stream.peek() method in Java 8 vs Java 9

It seems on every iteration of Java for the last few major releases, there are consistently new ways to manage concurrent tasks.

In Java 9, we have the [Flow API][1] which resembles the [Flowable API][2] of RxJava but with Java 9 has a much simpler set of classes and interfaces.

**Java 9**

Has a `Flow.Publisher`, `Flow.Subscriber`, `Flow.Processor`, `Flow.Subscription`, and `SubmissionPublisher`, and that&#39;s about it.

**RxJava**

Has whole *packages* of [Flow API][1]-like classes, i.e. `io.reactivex.flowables`, `io.reactivex.subscribers`, `io.reactivex.processors`, `io.reactivex.observers`, and `io.reactivex.observables` which seem to do something similar.

What are the main differences between these two libraries? Why would someone use the Java 9 Flow library over the much more diverse RxJava library or vice versa?

  [1]: https://docs.oracle.com/javase/9/docs/api/index.html?java/util/concurrent/Flow.html
  [2]: http://reactivex.io/RxJava/javadoc/index.html?io/reactivex/Flowable.html

Difference between RxJava API and the Java 9 Flow API

Java 9 (jdk-9+170) does not allow by default an application to see all classes from the JDK, unlike all previous versions of Java, due to the new module system.

To workaround this, the `java` command line offers a new argument `--add-exports` which allows to break encapsulation as follows:

`java -jar josm.jar --add-exports java.base/sun.security.util=ALL-UNNAMED --add-exports java.base/sun.security.x509=ALL-UNNAMED`

This is well explained in [JEP 261][1].

I have read about a similar option `--add-opens` using the same syntax, but the JEP 261 has not yet been updated to describe it (last update: 2017/03/08 13:58).

**What is the difference between these two options?**

**EDIT**: The [JEP 261][1] has been updated on 2017-09-22 to explain it.

  [1]: http://openjdk.java.net/jeps/261

What&#39;s the difference between --add-exports and --add-opens in Java 9?

What are the advantages of [compact strings][1] over compressed strings in JDK9?


  [1]: http://openjdk.java.net/jeps/254

Difference between compact strings and compressed strings in Java 9

Why does this code output `02` in [tag:java-8] but `o2` in [tag:java-9] or above?

    &quot;o2&quot;.replaceAll(&quot;([oO])([^[0-9-]])&quot;, &quot;0$2&quot;)

Why does String.replaceAll() work differently in Java 8 from Java 9?

My JDK 9+181 Spring Boot 2.0.0.BUILD-SNAPSHOT CLI application displays this warning on startup:

    WARNING: An illegal reflective access operation has occurred
    WARNING: Illegal reflective access by org.springframework.cglib.core.ReflectUtils$1 (jar:file:/home/jan/src/fm-cli/target/fm-cli-0.1.0-SNAPSHOT.jar!/BOOT-INF/lib/spring-core-5.0.0.RELEASE.jar!/) to method java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain)
    WARNING: Please consider reporting this to the maintainers of org.springframework.cglib.core.ReflectUtils$1

This is a console application, so I need to disable this warning -- how can I do that?

**Note:** This question asks the specific question of how to disable this warning triggered by Spring; it is not a duplicate of https://stackoverflow.com/questions/46230413/jdk9-an-illegal-reflective-access-operation-has-occurred-org-python-core-pysys which deals with a similar symptom in a different library.

Illegal reflective access by org.springframework.cglib.core.ReflectUtils$1

I was trying to understand jshell and fumbled to import external library. As of date I couldn&#39;t see any suggestion/solution for this. 

Can someone please let me know if already figured this out.

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