List&lt;String&gt; ids = new ArrayList&lt;String&gt;(); ids.add("1"); ids.add("2"); ids.add("3"); ids.add("4");   Now i want an output from this list as 1,2,3,4 without explicitly iterating over it.
While working in a Java app, I recently needed to assemble a comma-delimited list of values to pass to another web service without knowing how many elements there would be in advance. The best I could come up with off the top of my head was something like this:  public String appendWithDelimiter( String original, String addition, String delimiter ) {     if ( original.equals( "" ) ) {         return addition;     } else {         return original + delimiter + addition;     } }  String parameterString = ""; if ( condition ) parameterString = appendWithDelimiter( parameterString, "elementName", "," ); if ( anotherCondition ) parameterString = appendWithDelimiter( parameterString, "anotherElementName", "," );   I realize this isn't particularly efficient, since there are strings being created all over the place, but I was going for clarity more than optimization.  In Ruby, I can do something like this instead, which feels much more elegant:  parameterArray = []; parameterArray &lt;&lt; "elementName" if condition; parameterArray &lt;&lt; "anotherElementName" if anotherCondition; parameterString = parameterArray.join(",");   But since Java lacks a join command, I couldn't figure out anything equivalent.  So, what's the best way to do this in Java?
I'm stuck in a problem of mapping numbers from one range to another. I want to calculate popularity of a web page based on the number of page hits on a scale of 10. The problem is total number of web pages are around 41,00,000 and the web pages for which page visit is given are only 1,70,000. Also, the page visit for a web page is between 20,000 and 1.  Now, I'll try to rephrase the above problem in more mathematical problem, I have 41,00,000 objects for which I need to calculate some factor "po". Out of these 41,00,000 objects, 1,70,000 objects contain some number 20,000 &lt;=y &lt;= 1. Now how can I calculate "po" for each object on scale of 10.  The data mostly looks like,  O1: 20,000 O2: 17,000 O3: 16,000 . . . . . . . O19: 334 O20: 300 . . . . . . . On: 1 and so on......   Mostly, objects have page visits = 1.  I tried calculating page visit for each object/maximum page visit for an object but that gives me very small values(like 1/20,000 is a very small number). I want my resulatant po values to be at some distance from one another so that I can differentiate between them.  Can anyone please suggest me some solution ?  Thanks iOS 12 tapping on notification to open app not working If $\mid a_{jj}\mid \gt \sum_{i \neq j} \mid a_{ij} \mid$ then vectors $a_1,\dots ,a_n \in \mathbb{R}^n$ are linearly indendent. Let $a_1,\dots ,a_n \in \mathbb{R}^n$ with $a_i = (a_{i1}, \dots , a_{in})$.  Show that when $\mid a_{jj}\mid \gt \sum_{i \neq j} \mid a_{ij} \mid \; \forall \; j\in \{1,\dots ,n\}$, then $a_1,\dots ,a_n$ are linearly independent.  I want to show that the matrix \begin{matrix} a_{11} &amp; a_{21} &amp; \cdots &amp; a_{n1} \\ a_{12} &amp; a_{22} &amp; \cdots &amp; a_{n2} \\ \vdots &amp; &amp; \ddots &amp; \\ a_{1n} &amp; a_{2n} &amp; \cdots &amp; a_{nn} \end{matrix} can be transformed into an upper triangular matrix with all entries in the main diagonal $\neq 0$.  For the cases $n=1$ and $n=2$ this is easy. However, I fail to show this for the general case; the problem being that the tranformations mess up the coefficients such that I can't use the assumption on the $a_{jj}$'s anymore.  I'm pretty sure that this has already been solved somewhere on here, but I don't know how to search for it. Identification of mid-80s time travel tv show Make Applications (Ubuntu Software) to access all the DRIVES in my computer How to view the output of a running process in another bash session? I have left a script running on a remote machine from when I was locally working at it. I can connect over SSH to the machine as the same user and see the script running in ps.   $ ps aux | grep ipcheck myuser  18386  0.0  0.0  18460  3476 pts/0    S+   Dec14   1:11 /bin/bash ./ipchecker.sh   It is simply outputting to stdout on a local session (I ran ./ipchecker.sh form a local terminal window, no redirection, no use of screen etc).  Is there anyway from an SSH session I can view the output of this running command (without stopping it)?  So far the best I have found is to use strace -p 18386 but I get hordes of text flying up the screen, its far too detailed. I can stop strace and then sift through the output and find the text bring printed to stdout but its very long and confusing, and obviously whilst it's stopped I might miss something. I would like to find a way to see the script output live as if I was working locally.  Can anyone improve on this? The obvious answer is to restart the script with redirection or in a screen session etc, this isn't a mission critical script so I could do that. Rather though, I see this as a fun learning exercise. Why do I get a segmentation fault when writing to a "char *s" initialized with a string literal, but not "char s[]"? Suppose that $X$ and $Y$ are chosen randomly and independently according to the uniform distribution from $(0,1)$. Define $$ Z=\frac{\max(X,Y)}{\min(X,Y)}.$$ Compute the probability distribution function of $Z$. Can anyone give me some hints on how to proceed? I can only note that $\mathbb{P}[Z\geq 1]=1$ and $$F_Z(t)= \mathbb{P}[Z \leq t]=\mathbb{P}[X\leq Y, Y\leq tX]+\mathbb{P}[Y \leq X, x\leq tY]$$ Any nice, stable ways to keep a window 'Always on top' on the Mac? I am looking for a stable way to keep any window 'always on top' on OSX.  , an app that does that requires SIMBL/easySIMBL, which it seems is not very stable.  Are there any better solutions? It's actually surprising that there is no native way to implement this. Problems with pie charts There seems to be in increasing discussion about pie charts.   The main arguments against it seem to be:   Area is perceived with less power than length. Pie charts have very low data-point-to-pixel ratio   However, I think they can be somehow useful when portraying proportions. I agree to use a table in most cases but when you are writing a business report and you've just included hundreds of tables why not having a pie chart?  I'm curious about what the community thinks about this topic. Further references are welcome.  I include a couple of links:         In order to conclude this question I decided to build an example of pie-chart vs waffle-chart. How to apply CSS to iframe? Infectious chicken pox My 21 year old son has chicken pox and has been home for a few days now. The spots are just starting to crust over.  I work with elderly people but have had chicken pox as a child - should I carry on working while he is here (hes usually away at Uni) and infectious? How to capture text from the operating system in a practical and simple way? Sometimes we can't select the text to copy &amp; paste, such as dialog boxes.  Sometimes it's just not practical, such as 100 files inside a folder.  Is there any practical and simple way to capture those text from the system into a text file?  I'd wish to know both in OS X and Windows. Maybe it just can't be done today... Screen resolution stuck at 1024x768 How do I solve the following second order partial differential equation?  $4u_{xx}+5u_{xy}+u_{yy}+u_x+u_y=2$  I have classified the equation to be hyperbolic and changed variables to obtain the canonical form as $u_{\epsilon\nu}={1\over{3u_\nu}}-{8\over9}$ which I believe is correct but I am struggling to find the general solution? A step by step solution would be appreciated. What is the difference between a relative phase and a global phase? In particular, what is a phase? I know that $re^{i\theta} = x + iy$ for any complex number $x + iy$ by Euler's formula. How do you calculate relative and global phase? Warning when battery is fully charged I would like to get an alert (with sound) when my laptop battery is fully charged.  How can I do that? Creating unnumbered chapters/sections (plus adding them to the ToC and/or header) RSA encryption with private key and decryption with a public key Best choice between using \\ or leaving space after each paragraph to end the paragraph Here is the thing, I have always used a blank space between paragraphs in order to tell latex that there is a new paragraph. But there is someone I work with very often that keeps using \\ to break a line after a paragraph...  This is really annoying so I wanted to know if there is a real advantage of using \\ over just leaving a space.  Note that I am not referring to the paragraph environment, but to the simple term paragraph.