Java issues instantiating my LinkedList to my array. Data Structures course
What is a NullPointerException, and how do I fix it?
Is there anything special with complex fraction $\left|\frac{z-a}{1-\bar{a}{z}}\right|$? Is there anything special with the form:  $$\left|\frac{z-a}{1-\bar{a}{z}}\right|$$ ? With $a$ and $z$ are complex numbers.  In fact, I saw it in a problem:   If $|z| = 1$, prove that $|\frac{z-a}{1-\bar{a}{z}}| = 1$ If $|z| &lt; 1$ and $|a| &lt; 1$, prove that $|\frac{z-a}{1-\bar{a}{z}}| &lt; 1$   I can easily prove the first one with expansion:  $$z=\cos\theta + i\sin \theta \\ a = m +in$$  But it will be terrible to use in the second one. What's more, I found this form a little special so maybe there is some clever trick without using expansion?  Thank you a lot! Use physical harddisk in Virtual Box I am trying to prove that the affine hull of a set $X \subseteq \mathbb{R}^d$ is equal to the affine hull of the clojure of that set: $$ \text{aff}(X) = \text{aff}(\text{cl}(X)). $$  Proving $\text{aff}(X) \subseteq \text{aff}(\text{cl}(X))$ is easy, but containment in the other direction is harder.  I am assuming there is a sequence $\{ x_k \}_{k=1}^\infty \subseteq X$ such that $\lim_{k\to \infty} x_k = x^*$. The point $x^*$ is obviously contained in $\text{aff}(\text{cl}(X))$. But I am not sure how to show it is also in $\text{aff}(X)$, specifically because I am not sure how to show that $x^*$ lies on a line connecting two points in $X$.  Any suggestions on how to surmount this hurdle are welcome. How to remove duplicate values from an array in PHP I want to extend my volume. However the unallocated space lies ahead of the volume. Is it possible to extend this volume without converting it to a dynamic volume?     I tried to use diskpart with the extend command but it doesn't work. Makes sense because the instructions says that the unallocated space has to be behind the volume. How to Understand the Relationships Among Random Variables, Samples, and Populations? Why is it that when you add normally distributed random variables the variance gets larger but in the Central Limit Theorem it gets smaller? When you add two independent normal distributions the resulting distributions' variance is the sum of the variances i.e. it gets larger.  However, the Central Limit Theorem states that  when independent random variables are added, their properly normalized sum tends toward a normal distribution (informally a bell curve) even if the original variables themselves are not normally distributed.   and also says that as you add more variables the variance gets smaller. Why does the variance increase in one case but decrease in the other? Is it because in the CLT case the random variables come from the same underlying distribution? Is there a way to head/tail a document and get the reverse output; because you don't know how many lines there are in a document?  I.e. I just want to get everything but the first 2 lines of foo.txt to append to another document. Prove that $\left | \frac{a-b}{a+b}+\frac{b-c}{b+c}+\frac{c-a}{c+a} \right | < \frac{1}{8}.$ How to make a safe in vanilla Minecraft that locks and unlocks with a key? How can I make a safe/vault or something to lock my door that is very easy (as I am not that advanced with redstone) to keep people out of my house? Without mods? When should I use Inline vs. External Javascript? I would like to know when I should include external scripts or write them inline with the html code, in terms of performance and ease of maintenance.  What is the general practice for this?  Real-world-scenario - I have several html pages that need client-side form validation. For this I use a jQuery plugin that I include on all these pages. But the question is, do I:   write the bits of code that configure this script inline? include all bits in one file that's share among all these html pages? include each bit in a separate external file, one for each html page?   Thanks. pc ram memory 2x1GB or 1x2GB I don't know if it's the right place to ask but can somebody advise me for buying a ram memory for my computer.  I have a Dell Vostro 200 with 1GB of RAM and 667MHz. (2 x 512MB)  I want to buy raise the amount of RAM but I'm confused whether to buy 1 x 2GB or 2 x 1GB  I know it's the same for the available amount of memory but is ther a difference maybe in the clock speed so that 2 x 667MHz will be better than 1 x 667MHz. or maybe accessing one single memory slot will be faster and better than accessing two slots.  Please anyone helps. Code blocks are not prettified on mobile site On Chrome on Android, code blocks on the mobile site have no syntax highlighting, are not a monospaced font, and words are wrapped.  Mobile site on mobile browser:    Desktop site on mobile browser:    Inline code has the same issue, it isn't a monospaced font.  It has been this way for as long as I can remember. Wouldn't be surprised if this is a dupe. I'm using Dataloader to Upsert a Child Account to Parent Account using an external ID.  When the Upsert is complete, the Child overwrites the parent, it's not not connecting the Child Account to the Parent Account.  ((See Answer Below)) How to prove this sequent using natural deduction? How do I prove $$S\rightarrow \exists xP(x) \vdash \exists x(S\rightarrow P(x))$$ using natural deduction? Just an alignment of which axioms or rules that one could use would be much appreciated. Is there a difference between foo(void) and foo() in C++ or C? I'm a C++ guy learning Java. I'm reading Effective Java and something confused me. It says never to write code like this:  String s = new String("silly");   Because it creates unnecessary String objects. But instead it should be written like this:  String s = "No longer silly";   Ok fine so far...However, given this class:  public final class CaseInsensitiveString {     private String s;     public CaseInsensitiveString(String s) {         if (s == null) {             throw new NullPointerException();         }         this.s = s;     }     :     : }  CaseInsensitiveString cis = new CaseInsensitiveString("Polish"); String s = "polish";    Why is the first statement ok? Shouldn't it be   CaseInsensitiveString cis = "Polish"; How do I make CaseInsensitiveString behave like String so the above statement is OK (with and without extending String)? What is it about String that makes it OK to just be able to pass it a literal like that? From my understanding there is no "copy constructor" concept in Java? Convert a string to an enum in C# Delete commits from a branch in Git What is the plural of the abbreviation of "multiplicity automaton", "MA" or "MAs"? The "multiplicity automaton (MA)" is a model in compute science and its plural is "multiplicity automata". Should the plural of the abbreviation be MA or MAs?      is not a duplicate as it is focused on cases like "ATMs" where the expanded form "automated teller machines" has a regular plural ending in "s." Unlike "machines," the word "automata" has an irregular plural that does not end in "s." It's unclear from the linked answers how abbreviations that end in words like this should be pluralized. A high-ranking  mentions "VIPs," but a high-ranking  says     VIPs' is a strange one. It could be argued that the expanded acronym,   when pluralized, should be 'Very Important People' rather than 'Very   Important Persons'. Using this argument, 'VIP' could be used as a   singular or plural noun. "The VIP has arrived." "The VIP have   arrived." I'm not sure anyone else would agree with my logic, though.