I work on a project in Java for school, and I have a problem with JOptionPane.showInputDialog().  My question is: What does JOptionPane.showInputDialog() return if I enter nothing into the field and then hit "OK"?  I tried to find it out by myself with this test-code:  public static void main(String[] args) {     String test = JOptionPane.showInputDialog("Please enter:");     if (test==""){         System.out.println("Found it");     }else{         System.out.println(test);     } }   This doesn't work, as I said. It will print out the variable test, instead of the string "Found it".  What must I enter in the if-query in case I enter nothing in the field and then hit 'OK'?  Excuse my English, I'm Swiss.
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?
Einstein-Cartan theory - Book recommendation I want to delve into Cartan's formulation of General Relativity but it don't really know where to look. Does anyone have any book suggestions? system of ode with non-constant coefficient matrix How can I hide my code in visualforce page? Compiling a document with PGFplots processing only every x-th data point? Nautilus not generating thumbnails in 13.10 Like the title says, Nautilus is not generating thumbnails for any file types (pictures, documents, pdf, etc) after a clean install of 13.10.  I have checked the preferences and it is set to always generate thumbnails.  Help please! When used like this:  import static com.showboy.Myclass;  public class Anotherclass{}   what's the difference between import static com.showboy.Myclass and import com.showboy.Myclass? Difference between I and Me I am quite confused with the usage of I and me, Can anybody tell me what should be used in the following sentence: Your husband doesn't believe that You're older than (I / Me). I'm having serious problems installing the Broadcom drivers for Ubuntu. It worked perfectly on my previous version, but now, it is impossible.   What are the steps to install Broadcom wireless drivers for a BCM43xx card?  I'm a user with no advance knowledge in Linux, so I would need clear explanations on how to make, compile, etc.    lspci -vnn | grep Network showed:   Broadcom Corporation BCM4322 802.11a/b/g/n Wireless LAN Controller [14e4:432b]      iwconfig showed:  lo        no wireless extensions. eth0      no wireless extensions.   NOTE: Answer below is updated every time new information is added and confirmed working. Identification of particles and anti-particles The identification of an electron as a particle and the positron as an antiparticle is a matter of convention. We see lots of electrons around us so they become the normal particle and the rare and unusual positrons become the .  My question is, when you have made the choice of the electron and positron as particle and anti-particle does this automatically identify every other particle (every other fermion?) as normal or anti?  For example the proton is a particle, or rather the quarks inside are. By considering the interactions of an electron with a quark inside a proton can we find something, e.g. a conserved quantity, that naturally identifies that quark as a particle rather than an antiparticle? Or do we also just have to extend our convention so say that a proton is a particle rather than an antiparticle? To complete the family I guess the same question would apply to the neutrinos. How do I read a file into a std::string, i.e., read the whole file at once?  Text or binary mode should be specified by the caller. The solution should be standard-compliant, portable and efficient. It should not needlessly copy the string's data, and it should avoid reallocations of memory while reading the string.  One way to do this would be to stat the filesize, resize the std::string and fread() into the std::string's const_cast&lt;char*&gt;()'ed data(). This requires the std::string's data to be contiguous which is not required by the standard, but it appears to be the case for all known implementations. What is worse, if the file is read in text mode, the std::string's size may not equal the file's size.  A fully correct, standard-compliant and portable solutions could be constructed using std::ifstream's rdbuf() into a std::ostringstream and from there into a std::string. However, this could copy the string data and/or needlessly reallocate memory.    Are all relevant standard library implementations smart enough to avoid all unnecessary overhead?  Is there another way to do it?  Did I miss some hidden Boost function that already provides the desired functionality?     void slurp(std::string&amp; data, bool is_binary) I want to make sure all of the data in my plugins/themes is handled securely  before entering the database and before being output to the browser. My problem is that there are situations where the API handles the sanitization for you -- like when saving post meta fields -- and others where the plugin/theme author is wholly responsible for doing it -- like when saving custom settings.  For the scope of this question, I'm not concerned about validating data at the domain level -- e.g., checking that an Age field on a form is between 0 and 120, or that an e-mail address is valid. I'm only concerned about security -- e.g., escaping SQL queries to avoid SQL injection when saving to the database, or sanitizing data that's output to HTML templates to avoid XSS.  For output sanitization, I know that you always need to use functions like esc_html() and esc_attr() when echo'ing variables into HTML templates. But, what about when using ? Do they all sanitize the output already? If so, for which context (general HTML, tag attributes, etc)? Some functions have variants for different contexts (like the_title_attribute(), but most don't.  For input sanitization, I know that I need to use $wpdb-&gt;prepare() when making manual queries, but what about when using the Settings API to create a plugin settings page, or saving post meta fields for a custom post type?  Right now I've just been digging through Core and reading tutorials every time I use a function to find out if it sanitizes or not, but that's error-prone and time consuming. I'm hoping to find some kind of comprehensive list of all the possible situations and whether or not the API handles it. e.g.,  API validates/sanitizes   Saving post meta with update_postmeta() Saving user meta with update_user_meta() Outputting a post title - use the contextually appropriate variant of the_title() etc   You have to manually validate/sanitize   Saving plugin options with the Settings API. Pass a callback as the 3rd parameter of register_setting(). Direct database queries: Wrap the query in $wpdb-&gt;prepare(). Outputting variables in HTML. Use esc_attr(), esc_html(), etc etc   I'd also be interested to understand why the API provides it in certain situations, but not others. I'm assuming it has something to do with the unknown nature of the data, but would love to hear a thorough explanation. The Time That 2 Masses Will Collide Due To Newtonian Gravity My friend and I have been wracking our heads with this one for the past 3 hours... We have 2 point masses, $m$ and $M$ in a perfect world separated by radius r.  Starting from rest, they both begin to accelerate towards each other. So we have the gravitational force between them as:  $$F_g ~=~ G\frac{Mm}{r^2}$$  How do we find out at what time they will collide?  What we're having trouble with is this function being a function of $r$, but I have suspected it as actually a function of $t$ due to the units of $G$ being $N(m/kg)^2$.  I've tried taking a number of integrals, which haven't really yielded anything useful.  Any guidance?  No, this is not an actual homework problem, we're just 2 math/physics/computer people who are very bored at work :) How can I get exactly 5 logarithmic divisions of an interval? Can the term "etymology" be applied to a phrase or only individual words? I have always heard the term used in referring to a single word. When browsing questions on this site, I've seen it used applied to entire phrases, and have suppressed the compulsion to edit them and replace the term with origin. Deleted comments are persisting in the global inbox I realise that there is other questions out there about the  (First open one I found is ), but this is marked .  I often get the below issue where it will notify me about comments on my  (in this case what appears to be the user re-writing after deleting their comment) that no longer exist.  Also, occasionally, I see comment snippets with text that doesn't match what is on the page when I view it.  Let me know if I should be trying to edit that one to remove the tag indicating that it has been fixed, and add the above as another answer. Eigenvalues of symmetric matrices are real without (!) complex numbers Is there any proof of the fact that the eigenvalues of symmetric matrices (i.e. $A\in\mathbb{R}^{n\times n}$ with $A^t=A$) are real without the use of the concept of complex numbers? Formation of supermassive black holes Scientists have found very bright source of light which they call  and the are found to be . So these black holes are so massive that they cannot be formed by a supernova. So how are these formed? Is $D_n$, the dihedral group of order $2n$, isomorphic to a subgroup of $S_n$ ( symmetric group of $n$ letters) for all $n&gt;2$? Manual/automatic line breaks and text alignment in TikZ nodes sed delete option change of delimiter