According to [wikipedia](https://en.wikipedia.org/wiki/Universally_unique_identifier#Random_UUID_probability_of_duplicates), regarding the probability of duplicates in random UUIDs:

&gt; Only after generating 1 billion UUIDs every second for the next 100 years, the probability of creating just one duplicate would be about 50%. Or, to put it another way, the probability of one duplicate would be about 50% if every person on earth owned 600 million UUIDs.

I guess the same reasoning applies to Java&#39;s implementation of UUID. So no, you should not worry about this.

When I run Chrome browser using WebDriver, I am getting following message on console. Please let me know how to resolve it. 

&gt; &quot;Starting ChromeDriver (v2.10.267521) on port 22582 &quot; &quot;Only local
&gt; connections are allowed.&quot;

Here is my sample code:

&lt;!-- language: java --&gt;

    public class Browserlaunch {
    	public static void main(String[] args) {
        	System.setProperty(&quot;webdriver.chrome.driver&quot;, &quot;C:\\chromedriver_win32   \\chromedriver.exe&quot;);
    	    WebDriver driver = new ChromeDriver() ;
    		driver.get(&quot;http://webdunia.com&quot;);
        	driver.close();
    		driver.quit();
        }
    }



When running WebDriver with Chrome browser, getting message, &quot;Only local connections are allowed&quot; even though browser launches properly

I am new to C++. I often see conditional statement like below:

    if 
      statement_0;
    else if
      statement_1;

Question:

  **Syntactically**, shall I treat `else if` as a single keyword? Or is it actually an nested `if` statement within the outer `else` like below? 

    if 
      statement_0;
    else 
      if
        statement_1;

Is &quot;else if&quot; a single keyword?

I need to create some uniques files in Java and i plan to use UUID.randomUUID to generate their names. Is there any chance to get a collision for this? Should i do something like bellow os I shouldn&#39;t worry about this?

    Integer attemptsToGenerateUUID = 1;
    
    while (true) {
        UUID fileUUID = UUID.randomUUID();
    
        if (fileDoesNotExistwith this UUID name) {
            save file;
            break;
        }
    
        attemptsToGenerateUUID += 1;
    
        if (attemptsToGenerateUUID &gt; 64) {
            return false;
        }
    }


How big is the chance to get a Java UUID.randomUUID collision?

I need to create some uniques files in Java and i plan to use UUID.randomUUID to generate their names. Is there any chance to get a collision for this? Should i do something like bellow os I shouldn't worry about this?
<pre><code class="hljs language-ini">Integer attemptsToGenerateUUID = 1;

while (true) {
 UUID fileUUID = UUID.randomUUID();

 if (fileDoesNotExistwith this UUID name) {
 save file;
 break;
 }

 attemptsToGenerateUUID += 1;

 if (attemptsToGenerateUUID > 64) {
 return false;
 }
}
</code></pre>

There are a lot of useful new things in Java 8. E.g., I can iterate with a stream over a list of objects and then sum the values from a specific field of the `Object`&#39;s instances. E.g.

    public class AClass {
      private int value;
      public int getValue() { return value; }
    }
    
    Integer sum = list.stream().mapToInt(AClass::getValue).sum();

Thus, I&#39;m asking if there is any way to build a `String` that concatenates the output of the `toString()` method from the instances in a single line.


    List&lt;Integer&gt; list = ...
    
    String concatenated = list.stream().... //concatenate here with toString() method from java.lang.Integer class

    

Suppose that `list` contains integers `1`, `2` and `3`, I expect that `concatenated` is `&quot;123&quot;` or `&quot;1,2,3&quot;`.


Using streams to convert a list of objects into a string obtained from the toString method

I&#39;m a newbie to Java programming, trying to get the hang of OOP.

So I built this abstract class:

    public abstract class Vehicle{....}

and 2 subclasses:

    public class Car extends Vehicle{....}
    public class Boat extends Vehicle{....}

`Car` and `Boat` also hold some unique fields and methods that aren&#39;t common (don&#39;t have the same name, so I can&#39;t define an abstract method for them in Vehicle).

Now in mainClass I have setup my new Garage:

    Vehicle[] myGarage= new Vehicle[10];
	myGarage[0]=new Car(2,true);
	myGarage[1]=new Boat(4,600);

I was very happy with polymorphism until I tried to access one of the fields that are unique to Car, such as:

    boolean carIsAutomatic = myGarage[0].auto;

The compiler doesn&#39;t accept that. I worked around this issue using casting:
    
    boolean carIsAutomatic = ((Car)myGarage[0]).auto;

That works... but it doesn&#39;t help with methods, just fields. Meaning I can&#39;t do

    (Car)myGarage[0].doSomeCarStuff();

So my question is - what do I really have in my garage? I&#39;m trying to get the intuition as well as understand what&#39;s going on &quot;behind the scenes&quot;.


*****
for the sake of future readers, a short summary of the answers below:

1. Yes, there&#39;s a `Car` in `myGarage[]`
2. Being a static typed language, the Java compiler will not lend access to methods/fields that are non-&quot;Vehicle&quot;, if accessing those through a data structure based on the Vehicle super class( such as `Vehicle myGarage[]`)
3. As for how to solve, there are 2 main approaches below:
    1. Use type casting, which will ease the compiler&#39;s concerns and leave any errors in the design to run time
    2. The fact that I need casting says the design is flawed. If I need access to non-Vehicle capabilities then I shouldn&#39;t be storing the Cars and Boats in a Vehicle based data structure. Either make all those capabilities belong to Vehicle, or use more specific (derived) type based structures
4. In many cases, composition and/or interfaces would be a better alternative to inheritance. Probably the subject of my next question...
5. Plus many other good insights down there, if one does have the time to browse through the answers. 


Do I really have a car in my garage?

I was exploring `RecyclerView` and I was surprised to see that `RecyclerView` does not have `onItemClickListener()`.

I&#39;ve two question.

# Main Question

I want to know why Google removed `onItemClickListener()`? 

Is there a performance issue or something else?

# Secondary Question

I solved my problem by writing `onClick` in my `RecyclerView.Adapter`:

    public static class ViewHolder extends RecyclerView.ViewHolder implements OnClickListener {
        
        public TextView txtViewTitle;
        public ImageView imgViewIcon;
         
        public ViewHolder(View itemLayoutView) {
            super(itemLayoutView);
            txtViewTitle = (TextView) itemLayoutView.findViewById(R.id.item_title);
            imgViewIcon = (ImageView) itemLayoutView.findViewById(R.id.item_icon);
        }

		@Override
		public void onClick(View v) {
			
		}
    }

Is this ok / is there any better way?

Why doesn&#39;t RecyclerView have onItemClickListener()?

I&#39;m having issues trying to boot-up `Android Studio`

When I try to launch it after installation I&#39;m getting this error:

`No JVM Installation found. Please install a 64 bit JDK.`

----------

**My current system specification:**  

Operating System: `Windows 8.0 64 bit version`  
JDK installed: `JDK 1.8.0`  

----------

**What I have tried:**  

I have tried what was reported in the error, and also in most of the solutions to set the `JDK_HOME` variable in environment variables to my JDK path (64 bit version) i.e. `C:\Program Files\Java\jdk1.8.0_05`  

*`*I also have tried rebooting system, just in case to test if the environment variable is not working without a restart`*

----------

I have seen these solutions and tried but none of them works, so don&#39;t mark it as a duplicate of any of these:   
https://stackoverflow.com/questions/16574189/android-studio-installation-on-windows-7-fails-no-jdk-found  
https://stackoverflow.com/questions/20033231/with-android-studio-no-jvm-found-java-home-has-been-set  
https://stackoverflow.com/questions/16596520/android-studio-start-fails-on-windows-8-64bit  
https://stackoverflow.com/questions/16574544/android-studio-does-not-launch-after-installation

----------

Here is the cmd output for java version:

![enter image description here][1]


  [1]: http://i.stack.imgur.com/peGJ9.jpg

Android Studio - No JVM Installation found

I have always heard that C++ was way more efficient than Java (and that is why most games are developed in C++).

I wrote a small algorithm to solve the &quot;Eight queens puzzle&quot; in both Java and C++, using the exact same algorithm, and then started to raise the number or squares.
When reaching checkboards of 20*20 or even 22*22, it appears Java is much more effective (3 seconds vs 66 seconds for C++).

I have no idea why, but I am pretty beginning with C++, so it is possible I made some huge performance mistakes, so I will gladly accept any information that would help me understand what is happening.

Below is the code I use in Java:


    import java.awt.Point;
    import java.util.ArrayList;
    import java.util.List;

    public class HuitDames {

        /**
         * La liste des coordnn&#233;es des dames.
         */
        private static List&lt;Point&gt; positions = new ArrayList&lt;&gt;();

        /**
         * Largeur de la grille.
         */
        private static final int LARGEUR_GRILLE = 22;


        /**
         * @param args the command line arguments
         */
        public static void main(String[] args) {
            int i = 1;
            placerDame(i);
            for (Point point : positions) {
                System.out.println(&quot;(&quot; + point.x + &quot;; &quot; + point.y + &quot;)&quot;);
            }
        }

        /**
         * Place une dame et return true si la position est bonne.
         * @param i le num&#233;ro de la dame.
         * @return si la position est bonne.
         */
        private static boolean placerDame(int i) {

            boolean bonnePosition = false;
            for (int j = 1; j &lt;= LARGEUR_GRILLE &amp;&amp; bonnePosition == false; j++) {
                Point emplacement = new Point(i, j);
                positions.add(emplacement);
                if (verifierPrise(emplacement) &amp;&amp; (i == LARGEUR_GRILLE || placerDame(i + 1))) {
                    bonnePosition = true;
                }
                else {
                    positions.remove(i - 1);
                }
            }

            return bonnePosition;
        }

        /**
         * V&#233;rifie que la nouvelle position n&#39;est pas en prise avec une position d&#233;j&#224; pr&#233;sente.
         * @param position la position de la nouvelle dame.
         * @return Si la position convient par rapport aux positions des autres dames.
         */
        private static boolean verifierPrise(Point position) {
            boolean nonPrise = true;
            for (Point point : positions) {
                if (!point.equals(position)) {
                    // Cas o&#249; sur la m&#234;me colonne.
                    if (position.y == point.y) {
                        nonPrise = false;
                    }
                    // Cas o&#249; sur m&#234;me diagonale.
                    if (Math.abs(position.y - point.y) == Math.abs(position.x - point.x)) {
                        nonPrise = false;
                    }
                }
            }

            return nonPrise;
        }
    }

And below is the code in C++:

    #include &lt;iostream&gt;
    #include &lt;list&gt;
    #include &lt;math.h&gt;
    #include &lt;stdlib.h&gt;

    using namespace std;


    // Class to represent points.
    class Point {

        private:
            double xval, yval;

        public:
            // Constructor uses default arguments to allow calling with zero, one,
            // or two values.
            Point(double x = 0.0, double y = 0.0) {
                    xval = x;
                    yval = y;
            }

            // Extractors.
            double x() { return xval; }
            double y() { return yval; }
    };

    #define LARGEUR_GRILLE 22
    list&lt;Point&gt; positions;


    bool verifierNonPrise(Point emplacement) {
        bool nonPrise = true;
        for (list&lt;Point&gt;::iterator it = positions.begin(); it!= positions.end(); it++) {
            if (it-&gt;x() != emplacement.x()) {
                if (it-&gt;y() == emplacement.y()) {
                    nonPrise = false;
                }
                if (abs(it-&gt;y() - emplacement.y()) == abs(it-&gt;x() - emplacement.x())) {
                    nonPrise = false;
                }
            }
        }

        return nonPrise;
    }

    bool placerDame(int i) {
        bool bonnePosition = false;
        for (int j = 1; j &lt;= LARGEUR_GRILLE &amp;&amp; !bonnePosition; j++) {
            Point emplacement(i,j);
            positions.push_back(emplacement);
            if (verifierNonPrise(emplacement) &amp;&amp; (i == LARGEUR_GRILLE || placerDame(i + 1))) {
                bonnePosition = true;
            }
            else {
                positions.pop_back();
            }
        }

        return bonnePosition;
    }

    int main()
    {
        int i = 1;
        placerDame(i);
        for (list&lt;Point&gt;::iterator it = positions.begin(); it!= positions.end(); it++) {
            cout &lt;&lt; &quot;(&quot; &lt;&lt; it-&gt;x() &lt;&lt; &quot;; &quot; &lt;&lt; it-&gt;y() &lt;&lt; &quot;)&quot; &lt;&lt; endl;
        }
        return 0;
    }


Performance issue: Java vs C++

How can I get a device&#39;s unique ID in Swift?

I need an ID to use in the database and as the API-key for my web service in my social app. Something to keep track of this devices daily use and limit its queries to the database.

How to get a unique device ID in Swift?

Does anyone know of a good, solid, implementation of C# like GUID (UUID) in TypeScript?

Could do it myself but figured I&#39;d spare my time if someone else done it before.

A TypeScript GUID class?

I don&#39;t understand why

    SELECT UUID();
    
Returns something like:

    3f06af63-a93c-11e4-9797-00505690773f

But if I insert it into a binary(16) field (the UUID() function) with for instance a BEFORE INSERT trigger and run a select, it returns something like:

    0782ef48-a439-11

Note that these two UUIDs are not the same data.

I realize binary and an UUID string doesn&#39;t look identical, but shouldn&#39;t the selected data at least be just as long? Otherwise how can it possibly be equally likely to be unique?

Is it better to store it as char(36)? I just need it to be unique to prevent duplicate inserts. It is never selected or used for joins.

EDIT:

before trigger would be like:

    BEGIN
    
    if NEW.UUID IS NULL THEN
    
    NEW.UUID = UUID();
    
    END IF
    
    END

Inserting and selecting UUIDs as binary(16)

I am wondering if there is a way to generate the same UUID based on a `String.` 
I tried with UUID, it looks like it does not provide this feature.

Is there any way to generate the same UUID from a String

I am trying to get unique IDs for my Django objects.  In Django 1.8 they have the UUIDField.  I am unsure how to use this field in order to generate unique IDs for each object in my model.

Here is what I have for the UUIDField

    import uuid
    from django.db import models

    class MyUUIDModel(models.Model):
        id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)

    class Person(models.Model):
        ...
        unique_id = MyUUIDModel()

I can reproduce the id for the UUID model, but everytime I do I get the exact same id. For Example: 

    person = Person.objects.get(some_field = some_thing)
    id = person.unique_id.id

id then gives me the same id every time.  What is wrong, how do I fix this?  



Content Type	Original Author	Original Content on Stackoverflow
Question	daniels	View Question on Stackoverflow
Solution 1 - Java	Óscar López	View Answer on Stackoverflow

How big is the chance to get a Java UUID.randomUUID collision?

Java Problem Overview

Java Solutions

Solution 1 - Java

Is "else if" a single keyword?

When running WebDriver with Chrome browser, getting message, "Only local connections are allowed" even though browser launches properly

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