I have this book about Java and it is telling me if I use relational operators for objects such as strings it will turn out as false. Even if two strings have the same literal value. I tested this, yet true was printed. Could someone explain why this is?  String y = "Not null"; String x = "Not null";              if(x == y)                 System.out.println("True");
I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug.  Is == bad? When should it and should it not be used? What's the difference?
Can a script modify an environment variable of its calling shell? I am setting my JAVA_HOME in my ~/.bashrc file.  Now, I need to create a script that will change the JAVA_HOME just for the current terminal, so that I can start an app that needs java 5.  I have created this script to do this task, but after finishing, I can see that JAVA_HOME is not updated  export JAVA_HOME=/usr/lib/jvm/java-5-oracle/ export PATH=$PATH:$JAVA_HOME       Here is the result  $ ./javaHome5.sh $ echo $JAVA_HOME /usr/lib/jvm/java-6-oracle/   I think that the reason this is not being applied, is that a script is executing in it's own terminal, so when the script ends, the current terminal will not be affected.  Currently, the only way I've found around this is:   Edit my ~/.bashrc and change the JAVA_HOME var Run source ~/.bashrc to apply the changes in current terminal. Which again cannot be applied in a script, as the source command needs to be run in the current window.   Needless to say, this change applies to all new terminal windows, so I practically need to do this twice: One before starting my app, and one more time right after this, just to restore the environment vars to their default. That's not really convenient.  Do you have any ideas how can I change this var using a script? Does COVID-19 have a case fatality rate of 41%? Is this formula correct? According to the data on the , as of 3rd February 2020 there were 17491 confirmed cases of COVID-19 globally, 536 total recoveries and 362 deaths. From my non-expert calculation this implies a mortality rate of:  (Nd / (Nd + Nr)) * 100 = 41%  where:  Nd is the total number of deaths, Nr is the total number of full recoveries.  This leaves 16593 people still suffering from the disease who have neither recovered or died.  This is in stark contrast to the publicly disseminated value of ~2% mortality, so have I made a mistake in my calculation or assumptions, or is COVID-19 much more dangerous than commonly claimed?    [After a helpful discussion in the comments, 'mortality rate' is not the correct term to use here, instead I should say ''.] I thought it was by Heinlein or Brown, but if it was I can't locate it online.    The plot was aboard a spaceship, or maybe a space station, when an accident sends the astronauts spinning out of control towards certain doom.  One part of the story I remember distinctly was the one of the guys started screaming inconsolably and the noise was driving everyone crazy.  One of the astronauts made his way over to the guy and smashed his helmet so the screaming stopped.  As I recall, the story ends with the narrator turning off his comm link so he can ponder the beauty of the universe in silence.  Sound familiar to anyone? What makes a photo a good photo? I don't know if this is a stupid question, this just came across my mind.  Imagine a photo of a dog yawning.  Someone could say that is a very good photo as it is taken just at the right moment, from a perfect angle (eg. level with the dog) and it has a shallow depth of field focusing on its face.  Someone else might dislike it because unfortunately the dog is ugly.  So from that example I could say people look at the following elements when judging a photo (but I could be wrong):   The timing (if it's taken at the right moment) The angle it's taken from (composition?) DOF (composition?) The subject (eg. whether the dog is pretty)   I am interested to know what experts think the elements you look at when judging whether a photo is a good photo.  Thanks in advance for your comments. Puzzling Enumerable.Cast InvalidCastException The following throws an InvalidCastException.  IEnumerable&lt;int&gt; list = new List&lt;int&gt;() { 1 }; IEnumerable&lt;long&gt; castedList = list.Cast&lt;long&gt;(); Console.WriteLine(castedList.First());   Why?  I'm using Visual Studio 2008 SP1. Word for killing off or attempting to kill off an entire bloodline? I would like to know if there is a word or phrase for a systematic campaign to annihilate every descendant of a particular ancestor.   We have the word 'genocide' for killing off an entire race, and plenty of words for killing people based on how they are related to you (fratricide, filicide, et. al.), but looking over the  and the , I couldn't find a term for systematically killing an entire bloodline.   My question is prompted by a US news story about the horrific murder of 8 members of the same family, but those murders are not an example of what I'm thinking of because the children of the victims were left alive, so the motive for the killings was not to kill off the bloodline. The sense that some group had coordinated an attack against just one family is what made me wonder what the "not an entire race, just one bloodline" version of 'genocide' would be called.   Searching the Internet for "kill off" and bloodline sends me straight into the land of vampires, Illuminati, reptilian overlords, and, naturally, Priory of Sion nonsense so I haven't had much luck finding a thread to pull.   It may be that there is no word for it in the sense of murdering a human bloodline, because we just don't attempt kill off our royals down to the last heir often enough to coin a term for it. Maybe there is a scientific term for culling a line from a test population as part of biological research? Custom arrangement for fields with multiple values in Drupal 7 A Particular Two-Variable System in a Group Suppose $a$ and $b$ are elements of a group $G$. If $a^{-1}b^{2}a=b^{3}$ and $b^{-1}a^{2}b=a^{3}$, prove $a=e=b$.   I've been trying to prove but still inconclusive. Please prove to me.  Thanks very much for proof. What did Bill do to make Hanzo mad? Why did the First Order do this at the cantina? In The Force Awakens, after the First Order are alerted to BB-8, Rey, and Finn's presence at the cantina, an aerial bombardment of the compound begins. They also deploy ground troops.  Wouldn't it have been better to not have an aerial bombardment and simply have the troops surround the cantina, keeping as many people as possible bottled up inside it while they searched both the interior and surrounding area for BB-8?  Instead of a surgical extraction, the strategy that they chose seemed to create chaos and even risked destroying BB-8.  Perhaps this was a sign of the inexperience and emotionally-charged state of Kylo Ren, but General Hux seemed to have more direct authority over the deployment of troops and fighters.  So what was the strategy behind these tactics? Related:   This is a subtly different question because I'm not asking whether there's a historical relationship between the two lineages.  I am asking this question because answers to these questions:      are making assumptions about the appearance of Padme while pregnant, the period of gestation, and appearance of newborn babies.  All of these presuppose that the "humans" of the Star Wars Galaxy are 100% biologically equivalent to us.   In fact, as far as I know, we don't actually know any of those facts from canon.   (Do we?)   All we know is that "human" children and adults look like us.  So, do we have any canon or out-of-universe commentary that tells us that Star Wars humans and Earth humans are biologically equivalent?  Another way to put this would be  If presented with a Star Wars human and a Milky Way human, would the best doctors or the best medical droids be able to distinguish them? I'd like to get an advanced frame in Firefall. I've been told that I can use "Pilot Tokens" to unlock other frames without having to pay money.  How soon would I be able to unlock an advanced frame? Do I have to level a base frame all the way to level 40? More than once? Currently, moderators have the ability to reset a user's username and/or profile text, and propagate that to the rest of the network, resetting it everywhere. However, often, the user's stackexchange.com network profile will also need to be reset, and this is currently only possible to do by either the user in question or staff.  Instead of bothering staff every time, moderators should have something available similar to chat, where moderators can change a user's parent site and have access to a "refresh profile" button, which will fetch updated information such as username and avatar from the parent site.  Currently, the only thing that moderators can do on stackexchange.com is to see hidden accounts. It would make sense for moderators to be able to refresh profiles there, like chat, and avoid pinging CMs every time this comes up. Show that $\phi(n)=\frac{n}{2}$ if and only if $n=2^k$ for some positive integer k. I think I have it figured and would like to see if I am on the right track. Thank you. Why does the base-emitter voltage of a BJT decrease with temperature? According to Sedra/Smith Microelectronic Circuits, \$v_{BE}\$ changes by \$-2\text{mV}/\text{°C}\$. I cannot understand how this could possibly be the case given the equations I am familiar with.  With all currents kept constant, we have:  \$\large{i_E = \frac{I_s}{\alpha}e^{v_{BE}/V_T}}\$  To keep \$i_E\$ constant, any change in \$V_T\$ would have to be accompanied by a change of the same factor in \$v_{BE}\$, otherwise \$\alpha\$ or \$I_s\$ would have to change, which as far as I understand is not possible.  So, how can \$v_{BE}\$ be inversely proportional to \$V_T\$? Where can I find header files in C on unix If $x^n + a_{n-1}x^{n-1} + ... + a_0 = 0$ has a rational root, then such root is an integer Let $n &gt; 0$ and let $a_{n-1}, ..., a_0$ be integers. Prove that, if $x^n + a_{n-1}x^{n-1} + ... + a_0 = 0$ has a rational root, then such root is an integer.   I understand that posting questions without showing your work is frowned upon, but I don't know where to start with this one.. thanks in advance. Is Multiplying the Inverse Better or Worse? When dealing with double data types is multiplying by the inverse better or worse? Which way is faster? Which way uses less memory? Which way is preferred? How does MSIL handle this? SquareInches = MMSquared / 645.16  SquareInches = MMSquared * 0.0015500031000062000124000248000496    NB: 10K users will note that this is a duplicate of , which was deleted because the original question asker decided to berate everyone in the 'comments' section of the question.  This question was reposted because it is a 'good' question. Please 'uncheck' Community Wiki for your answer, as I'm only posting this as CW so that it's not seen as a 'reputation' grab. Related Question: There exists $C\neq0$ with $CA=BC$ iff $A$ and $B$ have a common eigenvalue Question:  Suppose $V$ and $W$ are finite dimensional vector spaces over $\mathbb{C}$. $A$ is a linear transformation on $V$,  $B$ is a linear transformation on $W$. Then there exists a non-zero linear map $C:V\to W$ s.t. $CA=BC$ iff $A$ and $B$ have a same eigenvalue.  ===========This is incorrect==========  Clearly, if $CA=BC$, suppose $Ax=\lambda x$, then $B(Cx)=CAx=C(\lambda x)=\lambda (Cx)$, so $A$ and $B$ have same eigenvalue $\lambda$. On the other hand, if $A$ and $B$ have a same eigenvalue $\lambda$, suppose $Ax=\lambda x, By=\lambda y$. Define $C:V\to W$ s.t. $Cx=y$, then $BCx=By=\lambda y=C\lambda x=CAx$. But I don't kow how to make $BC=CA$ for all $x\in V$.   ====================================== How to generate all permutations of a list?