Primitive data types cannot be `null`.  Only `Object` data types can be `null`.

`int`, `long`, etc... can&#39;t be `null`.

If you use `Long` (wrapper class for `long`) then you can check for `null`&#39;s:

    Long longValue = null;

    if(longValue == null)

If it is `Long` object then You can use `longValue == null` or you can use  `Objects.isNull(longValue)` method in Java 7+ projects .

Please check [Objects][1] for more info.


  [1]: https://docs.oracle.com/javase/8/docs/api/

If the `longValue` variable is of type `Long` (the wrapper class, not the primitive `long`), then yes you can check for null values.

A primitive variable needs to be initialized to some value explicitly (e.g. to `0`) so its value will never be null.

You can check Long object for null value with `longValue == null` ,
you can use  `longValue == 0L` for long (primitive), because default value of long is 0L, but it&#39;s result will be true if longValue is zero too

Of course Primitive types cannot be null. But in Java 8 you can use Objects.isNull(longValue) to check. 
Ex. If(Objects.isNull(longValue))

As mentioned already primitives can not be set to the Object type null.

What I do in such cases is just to use `-1` or `Long.MIN_VALUE`.

If it is Long you can check if it&#39;s null unless you go for long (as primitive data types cant be null while Long instance is a object)

&lt;!-- begin snippet: js hide: false console: true babel: false --&gt;

&lt;!-- language: lang-html --&gt;


    Long num; 

    if(num == null) return;

&lt;!-- end snippet --&gt;

For some context, you can also prefer using Optional with it to make it somehow beautiful for some use cases.
Refer https://stackoverflow.com/questions/22373696/requestparam-in-spring-mvc-handling-optional-parameters

As primitives(long) can&#39;t be null,It can be converted to wrapper class of that primitive type(ie.Long) and null check can be performed.

If you want to check whether long variable is null,you can convert that into Long and check,

    long longValue=null;
    
    if(Long.valueOf(longValue)==null)



I can&#39;t quite figure this out: I&#39;d like to delete all the records from a table on a matching query. Kind of like this.

    engine = sqlalchemy.create_engine(string)
    meta = MetaData(bind=engine)
    meta.reflect(bind=engine, schema=&#39;myschema&#39;)
    
    Base = automap_base(metadata=meta)
    Base.prepare(engine, reflect=True)
    Classes = Base.classes
    
    Session = sessionmaker(bind=engine)
    session = Session()
    
    session.delete(plays.record_id == &#39;123&#39;)

But that isn&#39;t working. What&#39;s the idea here? Error I get is:

`error in parsing record ID 020087: Class &#39;sqlalchemy.sql.elements.BinaryExpression&#39; is not mapped
`

python + SQLAlchemy: deleting with the Session object

I am a newbie in ASP.NET, and currently learning ASP.NET Identity. I know it&#39;s built on top of OWIN implementation by Microsoft, and I am also still learning that too. So, I came across the extension method CreatePerOwinContext in the Owin startup code, and I don&#39;t see a clear purpose of using it. Is it some kind of dependency injection container? What is the real purpose of the method? In what case it should be applied?

What is the purpose of the extension method CreatePerOwinContext in OWIN implementation by Microsoft

How do I check a Long value for null in Java?

Will this work? 


    if ( longValue == null) { return blah; }

How to check a Long for null in java

How do I check a Long value for null in Java?
Will this work?
<pre><code class="hljs language-ini">if ( longValue == null) { return blah; }
</code></pre>

How can I check if a `Stream` is empty and throw an exception if it&#39;s not, as a non-terminal operation?

Basically, I&#39;m looking for something equivalent to the code below, but without materializing the stream in-between. In particular, the check should not occur before the stream is actually consumed by a terminal operation.

    public Stream&lt;Thing&gt; getFilteredThings() {
        Stream&lt;Thing&gt; stream = getThings().stream()
                    .filter(Thing::isFoo)
                    .filter(Thing::isBar);
        return nonEmptyStream(stream, () -&gt; {
            throw new RuntimeException(&quot;No foo bar things available&quot;)   
        });
    }

    private static &lt;T&gt; Stream&lt;T&gt; nonEmptyStream(Stream&lt;T&gt; stream, Supplier&lt;T&gt; defaultValue) {
        List&lt;T&gt; list = stream.collect(Collectors.toList());
        if (list.isEmpty()) list.add(defaultValue.get());
        return list.stream();
    }

How to check if a Java 8 Stream is empty?

How can I register/add a custom shutdown routine that shall fire when my Spring Boot application shuts down?

Scenario: I deploy my Spring Boot application to a Jetty servlet container (i.e., no embedded Jetty). My application uses Logback for logging, and I want to change logging levels during runtime using Logback&#39;s MBean JMX configurator. [Its documentation states that to avoid memory leaks, on shutdown a specific LoggerContext shutdown method has to be called](http://logback.qos.ch/manual/jmxConfig.html#leak).

What are good ways to listen on Spring Boot shutdown events?

I have tried: 

    public static void main(String[] args) throws Exception {
        ConfigurableApplicationContext cac = SpringApplication.run(Example.class, args);

        cac.addApplicationListener(new ApplicationListener&lt;ContextClosedEvent&gt;() {

            @Override
            public void onApplicationEvent(ContextClosedEvent event) {
                logger.info(&quot;Do something&quot;);
            }
        });
    }

but this registered listener does not get called when the application shuts down.

Spring Boot shutdown hook

In Java 8, what&#39;s the difference between [`Stream.map()`][1] and [`Stream.flatMap()`][2] methods?


  [1]: http://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#map-java.util.function.Function-
  [2]: http://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#flatMap-java.util.function.Function-

What&#39;s the difference between map() and flatMap() methods in Java 8?

I tried:

    @RunWith(SpringJUnit4ClassRunner.class)
    @EnableAutoConfiguration(exclude=CrshAutoConfiguration.class)
    @SpringApplicationConfiguration(classes = Application.class)
    @WebAppConfiguration
    public class LikeControllerTest {

However the CRaSSHD still starts up. While currently it doesn&#39;t harm the test, I&#39;d like to disable unnecessary modules during unit testing to speed up and also avoid potential conflicts.

How to exclude *AutoConfiguration classes in Spring Boot JUnit tests?

Might be a strange question but indeed I would like to achieve a a bit more coverage on my tests and although I coded against a `JsonProcessingException` I can&#39;t create a payload that generates this exception, maybe because Jackson is quite smart and converts everything to a string, and even for bad strings it goes around the JSON specs. My problem is that Jackson is quite good :)

I basically want a payload that when I run this, it break with `JsonProcessingException`:


    String jsonPayload = objectMapper.writeValueAsString(payload);



I&#39;ve tried some like:

    HashMap&lt;String, String&gt; invalidJSONPayload= new HashMap&lt;&gt;();

    invalidJSONPayload.put(&quot;021&quot;,021);
    invalidJSONPayload.put(&quot;---&quot;,021);
    invalidJSONPayload.put(&quot;~&quot;,021);


I&#39;m not fussed with the type, so feel free to suggest another one. An empty object for example, throws `JsonMappingException` and I already catch that one as well.


How to get a JsonProcessingException using Jackson

I need to check if the recipient username is in file */etc/passwd* which contains all the users in my class, but I have tried a few different combinations of *if* statements and *[grep][1]* without success. The best I could come up with is below, but I don&#39;t think it&#39;s working properly.

My logic behind it is that if the *grep* is null, the user is invalid.

    send_email()
    {
      message=
      address=
      attachment=
      validuser=1
      until [ &quot;$validuser&quot; = &quot;0&quot; ]
        do
        echo &quot;Enter the email address: &quot;
        read address
        if [ -z grep $address /etc/passwd ]
          then
        validuser=0
        else
            validuser=1
        fi
        echo -n &quot;Enter the subject of the message: &quot;
        read message
        echo &quot;&quot;
        echo &quot;Enter the file you want to attach: &quot;
        read attachment
        mail -s &quot;$message&quot; &quot;$address&quot;&lt;&quot;$attachment&quot;
        done
        press_enter
    }

  [1]: https://en.wikipedia.org/wiki/Grep




How can I check if &#39;grep&#39; doesn&#39;t have any output?

I have the following query 

    SELECT  DISTINCT 
         pt.incentive_marketing, 
         pt.incentive_channel, 
         pt.incentive_advertising 
    FROM test.pricing pt 
    WHERE pt.contract_id = 90000 
    group by 1,2,3 
    order by pt.incentive_marketing;

The above query returns the o/p as shown in the attached image
![enter image description here][1]

**However I want to replace all null values by 0 using COALESCE**
Please let me know how this can be achieved in above SELECT query


Now I further modified the query using coalesce as below

    SELECT  
         COALESCE( pt.incentive_marketing, &#39;0&#39; ), 
         COALESCE(pt.incentive_channel,&#39;0&#39;), 
         COALESCE( pt.incentive_advertising,&#39;0&#39;) 
    FROM test.pricing pt 
    WHERE pt.contract_id = 90000 
    group by 1,2,3 

the result of which is as attached in image 2.

I still receive one row with blank values

![][2]


  [1]: http://i.stack.imgur.com/1mabt.jpg
  [2]: http://i.stack.imgur.com/6PZAw.jpg




Using COALESCE to handle NULL values in PostgreSQL

I know that `null` is an object with no attributes or functions.

However, I am confused that why `console.log(null == false);` and `console.log(null == true);` both return false.

What are the conversion rules between `null` and `boolean`?

Why (null == false) and (null == true) both return false?

I fail to understand how to correctly assure that something is not `nil` in this case:

    package main

    type shower interface {
      getWater() []shower
    }

    type display struct {
      SubDisplay *display
    }

    func (d display) getWater() []shower {
      return []shower{display{}, d.SubDisplay}
    }

    func main() {
      // SubDisplay will be initialized with null
      s := display{}
      // water := []shower{nil}
      water := s.getWater()
      for _, x := range water {
        if x == nil {
          panic(&quot;everything ok, nil found&quot;)
        }

        // First iteration display{} is not nil and will
        // therefore work, on the second iteration
        // x is nil, and getWater panics.
        x.getWater()
      }
    }

The only way I found to check if that value is actually `nil` is by using reflection.

Is this really wanted behaviour? Or do I fail to see some major mistake in my code?

[Play link here][1]

  [1]: http://play.golang.org/p/jHHXZbLH7e





Hiding nil values, understanding why Go fails here

Using Swift 1.1 and Xcode 6.2.

I have a UIStoryboard containing a singular, custom `UIViewController` subclass. On it, I have an `@IBOutlet` connection of type `UIView` from that controller to a `UIView` *subclass* on the storyboard. I also have similar outlets for subviews of that view. See figure A.

But at run time, these properties are nil (Figure B). Even though I have assured I&#39;ve connected the outlets in Interface Builder.

**Thoughts**:

- Is it possible that because I am using a subclass of a subclass something messes up with the initialization? I am not overriding any initializers
- `awakeFromNib:` is not getting called for some reason
- Maybe it doesn&#39;t connecting to subviews on subviews

**Things I have tried:**

- Matching `@IBOutlet` and storyboard item types exactly (instead of `UIView`)
- Deleting property and outlet and re-added them

![Figure A][1]

Figure A*

![Figure B][2]

Figure B

*The obscured code in `Figure A` is:

	@IBOutlet private var annotationOptionsView: UIView!
	@IBOutlet private var arrivingLeavingSwitch: UISegmentedControl!


  [1]: http://i.stack.imgur.com/U8Kpu.png
  [2]: http://i.stack.imgur.com/8CuUa.png

Thank you.

IBOutlet is nil, but it is connected in storyboard, Swift

I found both `long int long` and `int long long` can compile for a variable type. Is there any difference between `long int long`, `int long long` , `long long` and `long long int`?

In general, is the type identical if it has the same number of `long`?

**1 long:**

    long l;
    int long il;
    long int li;

**2 long:**

    long long ll;
    int long long ill;
    long int long lil;
    long long int lli;

Also if above is right, are the following declarations also identical?

    long long* llp;
    int long long* illp;
    long int long* lilp;
    long long int* llip;

Is &quot;long long&quot; = &quot;long long int&quot; = &quot;long int long&quot; = &quot;int long long&quot;?

I understand that both `java.lang.Long` and `java.math.BigInteger `can hold very large natural numbers.

I also know Long&#39;s max value, but what is the max value for BigInteger?

And aside from capacity, would BigInteger ever perform better when working with generally large integers that still fall in Long&#39;s range?

Question
--------

Is the only consideration: is my value too large for Long?

Long vs BigInteger

I am running the exact same code on both windows and mac, with python 3.5 64 bit. 

On windows, it looks like this:

    &gt;&gt;&gt; import numpy as np
    &gt;&gt;&gt; preds = np.zeros((1, 3), dtype=int)
    &gt;&gt;&gt; p = [6802256107, 5017549029, 3745804973]
    &gt;&gt;&gt; preds[0] = p
    Traceback (most recent call last):
      File &quot;&lt;pyshell#13&gt;&quot;, line 1, in &lt;module&gt;
        preds[0] = p
    OverflowError: Python int too large to convert to C long
    
However, this code works fine on my mac. Could anyone help explain why or give a solution for the code on windows? Thanks so much!

Content Type	Original Author	Original Content on Stackoverflow
Question	BrownTownCoder	View Question on Stackoverflow
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How to check a Long for null in java

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What is the purpose of the extension method CreatePerOwinContext in OWIN implementation by Microsoft

python + SQLAlchemy: deleting with the Session object

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