It&#39;s a [new feature](https://www.jetbrains.com/idea/whatsnew/#v2018-2-editor) of IntelliJ IDEA 2018.2:

**Underlining reassigned local variables and reassigned parameters**

IntelliJ IDEA now underlines reassigned local variables and reassigned parameters, by default. The attributes for all the languages supporting this feature, which for now include Java and Groovy, can be changed in **Preferences/Settings | Editor | Color Scheme | Language Defaults | Identifiers | Reassigned**.

[![underline][1]][1]

Why it may be useful?
---------------------

If the variable/parameter is underlined, you know that you can&#39;t use it in lambda/anonymous class directly.

When reading a very long method code, if the parameter is not underlined, you know for sure that its value is not reassigned anywhere in this method and it contains exactly the same value that was passed to this method at any point.

Some code guidelines are against reassigned variables and you may want to avoid them where possible to keep the code clean and make it easier to read/debug.

Nowadays many developers prefer to avoid mutable state, and reassign variables only in rare cases when it is really necessary. We don&#39;t want to manually enforce immutability, we suppose that everything is immutable by default and want to bring additional attention to the cases when something is not. If you use `final` to mark non-mutable variables it means that you need to write more code for regular cases and less code in exceptional cases. (BTW in modern languages declaring immutable variables doesn&#39;t require writing additional code, but unfortunately not in Java). 

Brian Goetz, Java Language Architect, also likes the way IntelliJ IDEA highlights reassigned variables (see [his tweet](https://twitter.com/BrianGoetz/status/1056640217682231296)).


  [1]: https://i.stack.imgur.com/kD1W7.png

Hope this screenshot would help.

[![enter image description here][1]][1]


  [1]: https://i.stack.imgur.com/wfKU4.jpg

If you know what is the [side effect in programming][1] then it will be easy for you. To protect your variable from the **side effect**, the IDE shows the underline as a warning to you. 


  [1]: https://softwareengineering.stackexchange.com/questions/40297/what-is-a-side-effect

Im am working on an app that requires a price input in `&#165;` and as such has no decimal places. 
If we use `keyboardType: TextInputType.numberWithOptions()` we can get a number pad input.
If we use `validator: (input) { }` we can check if input is valid but we cannot prevent it.

The problem is we can save a draft that will not need validation.
So it is better for us to only allow digit input in the first place.


    import &#39;package:flutter/material.dart&#39;;
    
    void main() =&gt; runApp(MyApp());
    
    class MyApp extends StatelessWidget {
      @override
      Widget build(BuildContext context) {
        return MaterialApp(
          title: &#39;Digits Only&#39;,
          theme: ThemeData(
            primarySwatch: Colors.blue,
          ),
          home: MyHomePage(title: &#39;Flutter Demo Home Page&#39;),
        );
      }
    }
    
    class MyHomePage extends StatefulWidget {
      MyHomePage({Key key, this.title}) : super(key: key);
    
      final String title;
    
      @override
      _MyHomePageState createState() =&gt; new _MyHomePageState();
    }
    
    class _MyHomePageState extends State&lt;MyHomePage&gt; {
      @override
      Widget build(BuildContext context) {
        return Scaffold(
          appBar: AppBar(
            title: Text(widget.title),
          ),
          body: Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                TextFormField(
                  autovalidate: true,
                  keyboardType: TextInputType.number,
                  validator: (input) {
                    final isDigitsOnly = int.tryParse(input);
                    return isDigitsOnly == null
                        ? &#39;Input needs to be digits only&#39;
                        : null;
                  },
                ),
              ],
            ),
          ),
        );
      }
    }

Is there a way to prevent certain text input and only allow digits?

Digit only TextFormField in Flutter

I try to compare below two dataframe with &quot;check_index_type&quot; set to False. According to the documentation, if it set to False, it shouldn&#39;t &quot;check the Index class, dtype and inferred_type are identical&quot;. Did I misunderstood the documentation? how to compare ignoring the index and return True for below test?

I know I can reset the index but prefer not to.

https://pandas.pydata.org/pandas-docs/stable/generated/pandas.testing.assert_frame_equal.html




    from pandas.util.testing import assert_frame_equal
    import pandas as pd
    d1 = pd.DataFrame([[1,2], [10, 20]], index=[0,2])
    d2 = pd.DataFrame([[1, 2], [10, 20]], index=[0, 1])
    assert_frame_equal(d1, d2, check_index_type=False)


    AssertionError: DataFrame.index are different
    DataFrame.index values are different (50.0 %)
    [left]:  Int64Index([0, 2], dtype=&#39;int64&#39;)
    [right]: Int64Index([0, 1], dtype=&#39;int64&#39;)

how to ignore index comparison for pandas assert frame equal

Since the new update (2018.2) IntelliJ IDEA underlines variables, when they are &quot;unnecessarily&quot; reassigned - this includes, however, each use of &quot;+=&quot;.&lt;br&gt;
Is this a mistake in the IDE or am I getting it wrong?&lt;br&gt;
Please see this basic method as an example. (It just adds a list of numbers.)&lt;br&gt;

[![example image][1]][1]


  [1]: https://i.stack.imgur.com/bxLKB.png

IntelliJ IDEA underlines variables when using += in JAVA

Since the new update (2018.2) IntelliJ IDEA underlines variables, when they are "unnecessarily" reassigned - this includes, however, each use of "+=". 
Is this a mistake in the IDE or am I getting it wrong? 
Please see this basic method as an example. (It just adds a list of numbers.) 
<a href="https://i.stack.imgur.com/bxLKB.png" target="_blank" rel="noopener noreferrer"><img src="https://i.stack.imgur.com/bxLKB.png" alt="example image"></a>

JDK-11 will remove a lot of older parts of the JDK ([JEP-320][1]).
For some of them (e.g. JAXB) functionality will be provided as regular library. You simply add another dependency and everything works fine again.

But not so for CORBA, because

&gt; There is no significant interest in developing modern applications with CORBA in Java

I am however in the painful situation of needing to maintain older applications that still require CORBA while still wanting to update to JDK-11.

Is there a replacement-library out there or another good way of migrating to JDK-11 without removing the CORBA functionality of these applications?


  [1]: http://openjdk.java.net/jeps/320 &quot;JEP-320&quot;

Is there a replacement library for CORBA in JDK 11

`FragmentManager` is deprecated. Is there an alternative or what can I do now?


     PlaceAutocompleteFragment autocompleteFragment = (PlaceAutocompleteFragment) getFragmentManager().findFragmentById(R.id.place_autocomplete_fragment);
            autocompleteFragment.setOnPlaceSelectedListener(new PlaceSelectionListener() {
                @Override
                public void onPlaceSelected(Place place) {
                    // TODO: Get info about the selected place.
                    destination = place.getName().toString();
                    destinationLatLng = place.getLatLng();
                }
                @Override
                public void onError(Status status) {
                    // TODO: Handle the error.
                }
            });


![deprecation strike image][1]


  [1]: https://i.stack.imgur.com/nrXaD.jpg

Since the Android getFragmentManager() API is deprecated, is there any alternative?

Asking this question to clarify my understanding of type classes and higher kinded types, I&#39;m not looking for workarounds in Java.

---

In Haskell, I could write something like

&lt;!-- language: haskell --&gt;

    class Negatable t where
        negate :: t -&gt; t

    normalize :: (Negatable t) =&gt; t -&gt; t
    normalize x = negate (negate x)

Then assuming `Bool` has an instance of `Negatable`, 

&lt;!-- language: haskell --&gt;

    v :: Bool
    v = normalize True

And everything works fine.

---

In Java, it does not seem possible to declare a proper `Negatable` interface. We could write:

    interface Negatable {
        Negatable negate();
    }

    Negatable normalize(Negatable a) {
        a.negate().negate();
    }

But then, unlike in Haskell, the following would not compile without a cast (assume `MyBoolean` implements `Negatable`):

    MyBoolean val = normalize(new MyBoolean()); // does not compile; val is a Negatable, not a MyBoolean

**Is there a way to refer to the implementing type in a Java interface, or is this a fundamental limitation of the Java type system?** If it is a limitation, is it related to higher-kinded type support? I think not: it looks like this is another sort of limitation. If so, does it have a name?

Thanks, and please let me know if the question is unclear!

Can I define the Negatable interface in Java?

I&#39;ve been using `Random (java.util.Random)` to shuffle a deck of 52 cards. There are 52! (8.0658175e+67) possibilities. Yet, I&#39;ve found out that the seed for `java.util.Random` is a `long`, which is much smaller at 2^64 (1.8446744e+19). 

From here, I&#39;m suspicious whether `java.util.Random` *is really that random*; is it actually capable of generating all 52! possibilities?

If not, how can I reliably generate a better random sequence that can produce all 52! possibilities?

Is java.util.Random really that random? How can I generate 52! (factorial) possible sequences?

To test a component/bean in a Spring Boot application, [the testing part of the Spring Boot documentation][1] provides much information and multiple ways :
`@Test`, `@SpringBootTest`, `@WebMvcTest`, `@DataJpaTest` and still many other ways.  
Why provide so many ways ? 
How decide the way to favor ?   
Should I consider as integration tests my test classes annotated with Spring Boot test annotations such as `@SpringBootTest`, `@WebMvcTest`, `@DataJpaTest`  ? 


PS : I created this question because I noticed that many developers (even experienced) don&#39;t get the consequences to use an annotation rather than another.   

  [1]: https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-testing.html

How to test a component / bean in Spring Boot

Consider a standard for loop:

```
for (int i = 0; i &lt; 10; ++i) 
{
   // do something with i
}
```

I want to prevent the variable `i` from being modified in the body of the `for` loop. 

However, I cannot declare `i` as `const` as this makes the increment statement invalid. Is there a way to make `i` a `const` variable outside of the increment statement?


How to make a for loop variable const with the exception of the increment statement?

I&#39;m having trouble getting IntellJ to recognize JavaFX packages. With a new JavaFX project, with OpenJDK 11, when trying to build the project, IntelliJ can&#39;t recognize the JavaFX packages.

I&#39;ve imported `openjfx:javafx-base-11` from the Maven repo.

I&#39;ve looked at other questions and the solutions seem to range from checking that the bytecode is at the right level (mine is), and that the project language is correct (mine is).

Anyone have any ideas?

[![pic 1][1]][1]

[![pic 2][2]][2]

[![pic 3][3]][3]

**Edit:**

Error:

[![enter image description here][4]][4]


  [1]: https://i.stack.imgur.com/C0VJq.png
  [2]: https://i.stack.imgur.com/3XJNw.png
  [3]: https://i.stack.imgur.com/j2B8G.png
  [4]: https://i.stack.imgur.com/C2PE5.png

IntelliJ can&#39;t recognize JavaFX 11 with OpenJDK 11

I have an odd problem with Android Studio.
Here is how my class file looks like on Android Studio

[![][1]][1]


And here is what it looks like on a text editor.

[![enter image description here][2]][2]


  [1]: https://i.stack.imgur.com/4LxRp.png
  [2]: https://i.stack.imgur.com/FMjPa.png

Any ideas why it is happening? I have tried closing then reimporting the project, invalidate caches and restart, clean project, build project, delete .idea folder and .iml files. All of my files are broken when opening in AS but looks fine on text editors.

Android Studio shows wrong file contents

I am trying to build an application which was built using java 8, now it&#39;s upgraded to java 11. I installed [Java 11][1] using [an oracle article][2] in my **windows machine** and I use **IntelliJ IDEA 2017** as my IDE.

I changed my system environment variables and set the 

    JAVA_HOME to C:\Program Files\Java\jdk-11.0.1
And added that to the `Path` variable.

    C:\&gt;java -version
    java version &quot;11.0.1&quot; 2018-10-16 LTS
    Java(TM) SE Runtime Environment 18.9 (build 11.0.1+13-LTS)
    Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.1+13-LTS, mixed mode) 

When I build my application in IntelliJ, this is what I get:

    Information:java: Errors occurred while compiling module &#39;test-domain_main&#39;
    Information: javac 1.8.0_171 was used to compile java sources
    Information:1/10/2019 4:21 PM - Compilation completed with 1 error and 0 warnings in 1s 199ms
    Error:java: invalid target release: 11

This is what I&#39;ve tried so far:

 1. I changed `.idea/compiler.xml` target values from 8 to 11 but that didn&#39;t help. Also, verified the `Target bytecode version` in `settings &gt; Build, Execution, Deployment &gt; Compiler &gt; Java Compiler` and all my modules are set to 11. 

 2. Went to `file &gt; Project Structure &gt; SDKs *(currently I have 1.7 and 1.7 listed)* &gt; Add new SDK &gt; JDK &gt;`
After that, I selected `C:\Program Files\Java\jdk-11.0.1` But it errors out with &quot;The selected directory is not a valid home for JDK&quot;

I am not sure if I installed the wrong JDK 11, because in my `C:\Program Files\Java\`, I see separate JDK and JRE folders for `1.7` and `1.8` but only JDK folder for `11.0.1`

Or is it something else I need to change? 

  [1]: https://www.oracle.com/technetwork/java/javase/downloads/index.html
  [2]: https://docs.oracle.com/en/java/javase/11/install/installation-jdk-microsoft-windows-platforms.html#GUID-A7E27B90-A28D-4237-9383-A58B416071CA

Error: Java: invalid target release: 11 - IntelliJ IDEA

Recently I switched to the Java 11 and start to debug my app and saw this message:

&gt; OpenJDK 64-Bit Server VM warning: Sharing is only supported for boot
&gt; loader classes because bootstrap classpath has been appended

Found only [this commit][1] and [ticket][2], but it doesn&#39;t tell me much. 

Do I need to worry about it?


  [1]: http://hg.openjdk.java.net/jdk/jdk/rev/18fba780c1d1
  [2]: https://bugs.openjdk.java.net/browse/JDK-8203031

How to avoid &quot;Sharing is only supported for boot loader classes because bootstrap classpath has been appended&quot; warning during debug with Java 11?

I followed the steps in the Flutter document and tried to build my first Flutter app in Intellij IDEA. And when I try to run it,there was an error about my JAVA_HOME variable. And an error about cannot resolve symbol &quot;Properties&quot; in the build.gradle file. I really don&#39;t know what to do.

This is my error information displayed in the Console window.

    Launching lib\main.dart on Android SDK built for x86 in debug mode...
    Initializing gradle...
    Finished with error: ProcessException: Process 
    &quot;F:\untitled\android\gradlew.bat&quot; exited abnormally:

    ERROR: JAVA_HOME is set to an invalid directory: F:\Google download\jdk- 
    10.0.1_windows-x64_bin.exe

    Please set the JAVA_HOME variable in your environment to match the
    location of your Java installation.
      Command: F:\untitled\android\gradlew.bat -v

Actually there is nothing wrong with my JAVA_HOME variable, I set it to the proper directory: C:\Program Files (x86)\Java\jdk1.8.0_131.

And I run the command it shows above &quot;F:\untitled\android\gradlew.bat -v&quot;, it seemed to update the gradle version, but the error didn&#39;t resolved.

And this is the code in build.gradle file.

```
def localProperties = new Properties() 
//there will be a highlight on Properties indicates that &#39;cannot resolve symbol &quot;Properties&quot; &#39;

def localPropertiesFile = rootProject.file(&#39;local.properties&#39;)
if (localPropertiesFile.exists()) {
    localPropertiesFile.withReader(&#39;UTF-8&#39;) { reader -&gt;
        localProperties.load(reader)
    }
}

def flutterRoot = localProperties.getProperty(&#39;flutter.sdk&#39;)
if (flutterRoot == null) {
    throw new GradleException(&quot;Flutter SDK not found. Define location with flutter.sdk in the local.properties file.&quot;)
//the same as the Properties on GradleException
}

def flutterVersionCode = localProperties.getProperty(&#39;flutter.versionCode&#39;)
if (flutterVersionCode == null) {
    flutterVersionCode = &#39;1&#39;
}

def flutterVersionName = localProperties.getProperty(&#39;flutter.versionName&#39;)
if (flutterVersionName == null) {
    flutterVersionName = &#39;1.0&#39;
}

apply plugin: &#39;com.android.application&#39;
apply from: &quot;$flutterRoot/packages/flutter_tools/gradle/flutter.gradle&quot;

android {
    compileSdkVersion 28

    lintOptions {
        disable &#39;InvalidPackage&#39;
    }

    defaultConfig {
        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
        applicationId &quot;com.example.untitled&quot;
        minSdkVersion 16
        targetSdkVersion 28
        versionCode flutterVersionCode.toInteger()
        versionName flutterVersionName
        testInstrumentationRunner &quot;android.support.test.runner.AndroidJUnitRunner&quot;
    }

    buildTypes {
        release {
            // TODO: Add your own signing config for the release build.
            // Signing with the debug keys for now, so `flutter run --release` works.
            signingConfig signingConfigs.debug
        }
    }
}

flutter {
    source &#39;../..&#39;
}

dependencies {
    testImplementation &#39;junit:junit:4.12&#39;
    androidTestImplementation &#39;com.android.support.test:runner:1.0.2&#39;
    androidTestImplementation &#39;com.android.support.test.espresso:espresso-core:3.0.2&#39;
}
```

Content Type	Original Author	Original Content on Stackoverflow
Question	fandango	View Question on Stackoverflow
Solution 1 - Java	CrazyCoder	View Answer on Stackoverflow
Solution 2 - Java	Enrico Giurin	View Answer on Stackoverflow
Solution 3 - Java	Gk Mohammad Emon	View Answer on Stackoverflow

IntelliJ IDEA underlines variables when using += in JAVA

Java Problem Overview

Java Solutions

Solution 1 - Java

Why it may be useful?

Solution 2 - Java

Solution 3 - Java

how to ignore index comparison for pandas assert frame equal

Digit only TextFormField in Flutter

Attributions