Hi I'm very new to Java and have this HW problem, we are asked to build a Class RandomBag -- a generic bag container which allows 'RandomPick' of an element. I keep getting this error I have little idea to fix, any help is greatly appreciated!     public RandomBag() {       ArrayList&lt;E&gt; Bag=new ArrayList&lt;E&gt;();       Random Rand =new Random();   }   public RandomBag(int seed) {        ArrayList&lt;E&gt; Bag=new ArrayList&lt;E&gt;();       Random Rand =new Random(seed);
What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?
How was the bank robbery completed? In Now You See Me, when Morgan Freeman explains to the detective on how the Four Horseman robbed the bank, he mentions that they replaced the real money (while in the secured transport truck) with flash paper.  This does not explain how the paper in the bank got ignited, and no ignition/stimulator left in the scene as evidence.  Who/What/When ignited the flash paper in the bank on time?   There had to be some timer/delay mechanism on the platform, or something similar - but in the frames we see - there is nothing. Can somebody tell me why the counting measure (so, if $S=P(X)$, then $\mu(A)$=infinity if $A$ isn't finite and $\mu(A)=$#$A$ if $A$ is finite) is a measure? (The second property of a measure isn't clear for me). This is the third time I've tried to install Ubuntu Server 14.04.03 64-bit on the same laptop, and each time it caused different problems.  Each time I wrote the same iso image to a USB flash drive by using a different application and OS.   Universal USB Installer (pendrivelinux.com) from Windows WinImage writer from Windows built-in image writer from Linux Mint 17.2    The iso image is the same in all three cases, the USB flash drive is the same, and the laptop is the same. However each time the installation of Ubuntu gave me different installation options. For example, the last time I installed Ubuntu, it didn't show all the packages to choose while installing (Basic Ubuntu server, etc.). How do I redirect to another webpage? As I understand it, electromagnetic waves have two components which are the result of each other, i.e., when a moving electric charge creates a changing magnetic field at point X then a changing electric field is created at point Y and this repeating process is what creates EM waves, so therefore, it requires no medium. Is my understanding correct?  One thing that I'm surprised to know is that light is also called an electromagnetic wave.  Does this include light of any kind, for example: light from a bulb, a tube, and also from the Sun? How do they contain electric and magnetic fields? How to retrieve GET parameters from JavaScript Am I required to pay UK/ USA Visa fees if I have a German residence permit? Here is the situation. I am non-european but staying in Germany with a Residence permit. I can visit all Schengen listed countries with no issue. Assuming that I would want to travel to a non-Schengen country e.g. UK or USA, can I use my residence permit to travel there or am I required to apply as a citizen of my country? Assuming Germans are not required to pay Visa fees to that country, will I have to pay since I only have a residence permit? Third case, Europeans can fly directly to the airport of some countries and apply for a visa from there. In some other countries, you are required to book a Visa appointment at the embassy, which may be granted or not. Does that apply for one with a residence permit? jquery's append not working with svg element? Is there a pronoun I can use as a gender-neutral pronoun when referring back to a singular noun phrase?  Each student should save his questions until the end. Each student should save her questions until the end. It would be nice to  for .  As it is, SE kind of stands out (in a not cool way): My server had been infected and the attacker spread a bunch of .5randomletters folders around my file system, with malicious code inside of them. I want to search for all the folders that begin with a dot, review them and then remove them.  How can I do that? When should we use "and" and/or "and/or"? What's the difference between "and" and "and/or"?  How do we decide whether to use one or the other?  Note: Also it would be great if someone could explain how do we actually pronounce "and/or" verbally in a sentence... Permission denied to change gid(group) of a file I own It appears I still miss some things about the way permissions work. I am on a debian 7 system btw. just now I have this file of which I downloaded and it belongs to myuser:myuser, that is both user and group are set to me. It also resides in my $HOME directory since that is where I downloaded it to.  So far so good. Now I want to share this file with some other users of the pc and for that I want to switch the group ownership of the file to group "users". however that fails:  nass@quarx:~/xmas_carol$ chgrp -R users *  chgrp: changing group of movie.mov': Operation not permitted   And the contents of the folder are:  -rwxr-xr-x 1 nass nass 2482411461 Feb  6 03:57 movie.mov   I am fuzzy about what is going on with the permissions. Can someone explain How to check if PHP array is associative or sequential? PHP treats all arrays as associative, so there aren't any built in functions. Can anyone recommend a fairly efficient way to check if an array contains only numeric keys? Basically, I want to be able to differentiate between this: $sequentialArray = [     'apple', 'orange', 'tomato', 'carrot' ];  and this: $assocArray = [     'fruit1' =&gt; 'apple',     'fruit2' =&gt; 'orange',     'veg1' =&gt; 'tomato',     'veg2' =&gt; 'carrot' ]; How can I chroot sftp-only SSH users into their homes? I want to give a client access to my server, but I want to limit those users to their home directories. I will bind-mount in any files I want them to be able to see.  I've created a user called bob and added him to a new group called sftponly. They have a home directory at /home/bob. I've changed their shell to /bin/false to stop SSH logins. Here is their /etc/passwd line:  bob:x:1001:1002::/home/bob:/bin/false   I've also changed the /etc/ssh/sshd_config to include the following:  Match Group sftponly         ChrootDirectory /home/%u         ForceCommand internal-sftp         AllowTcpForwarding no   When I try to log in as them, here's what I see   $ sftp bob@server bob@server's password:  Write failed: Broken pipe Couldn't read packet: Connection reset by peer   If I comment out the ChrootDirectory line I can SFTP in but then they have free rein over the server. I have found that ChrootDirectory /home works, but it still gives them access to any home directory. I have explicitly tried ChrootDirectory /home/bob but that doesn't work either.  What am I doing wrong? How can I limit bob to /home/bob/?  ----EDIT-----  Okay so I just had a look at /var/log/auth.log and saw this:  May  9 14:45:48 nj sshd[5074]: pam_unix(sshd:session): session opened for user bob by (uid=0) May  9 14:45:48 nj sshd[5091]: fatal: bad ownership or modes for chroot directory component "/home/bob/" May  9 14:45:48 nj sshd[5074]: pam_unix(sshd:session): session closed for user bob   I'm not entirely sure what's going on there,  but it suggests something is wrong with the user directory. Here is the ls -h /home output:  drwxr-xr-x 26 oli      oli      4096 2012-01-19 17:19 oli drwxr-xr-x  3 bob      bob      4096 2012-05-09 14:11 bob In SF1, Stop refreshing the embedded vf page on a layout Below is my VF page which is embedded on a layout. In SF1 mobile app, it's getting refreshed whenever we touch on it. How can I avoid refreshing the VF page while touching it on the screen? In Desktop it's working fine. Please provide your inputs. &lt;apex:page standardController=&quot;PremiseObj__c&quot; lightningStylesheets=&quot;true&quot;&gt; &lt;apex:includeLightning /&gt; &lt;apex:slds /&gt; &lt;div id=&quot;premiseServDetails&quot;&gt; &lt;/div&gt; &lt;script&gt; window.onload = function (){     $Lightning.use(&quot;c:PremiseObjUpdateApp&quot;, function() {         $Lightning.createComponent(&quot;c:PremiseObjUpdatecmp&quot;,                                    {                                         recordId : &quot;{!Premiserecord__c.Id}&quot;                                     },                                    &quot;premiseServDetails&quot;,                                    function(cmp,event) {                                        setTimeout(function() {                                            //document.getElementById('loading').style.display = 'none';                                        }, 3000);                                    });     }); } &lt;/script&gt; &lt;/apex:page&gt; Configure up-arrow to browse through commands with same initial characters rather than all previous commands On the bash command-line, ↑ gives me the previous command. On the command-lines in ipython or matlab, when I type a few characters, ↑ gives me the previously entered command starting with those characters. How can I enable exactly this behaviour in bash? I am aware of more advanced ways of searching through the command-line history, but sometimes a simple way is more convenient. Decrease Backlight Below Minimum I have this laptop that doesn't handle the backlight very well.  In /etc/default/grub, I have added a acpi_backlight=vendor function to get it to work at all. Which is cool, and the backlight now actually works, but the minimum backlight setting is still pretty high.  Is there any way to decrease the backlight below minimum? I don't mind having to type in the terminal to do that, as I won't need to do it often (just at night etc.) I am afraid that listing doesn't support javascript.  \begin{lstlisting}[language=javascript] ... \end{lstlisting}   What am I doing wrong? How best to include other scripts?