Null Pointer Exception Java Shopping Cart "sort" Method For a school assignment, we have to make a Shopping cart class, along with an Item class and a runner. I figured out how to print out a receipt for items the user enters, but one thing I can't figure out is how to write a sort method using insertion Sorting, which orders each item in the cart by its total cost (price * quantity)  Here is my error:  java.lang.NullPointerException     at ShoppingCart.sort(ShoppingCart.java:54)     at Shopping.main(Shopping.java:32)   I went back to the lines stated  ShoppingCart: (line 54)  public void sort() {     double temp;     int pos = 0;     for (int i = 1;i&lt; cart.length;i++){       temp = cart[i].itemPrice(); //line 54       pos = i;       while (pos&gt;0 &amp;&amp; temp &lt; cart[pos-1].itemPrice()) {         cart[pos] = cart[pos-1];         pos--;       }       cart[pos] = cart[i];     }   }   Shopping: (line 32)   cart.sort();   And here is my method to get the price in the Item Class  public double itemPrice(){      return total; }   I'm not sure how to fix the Null Pointer Exception error.
What is a NullPointerException, and how do I fix it? 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?
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Here's the method provided:  unsigned int getbits(unsigned int x, int p, int n) {     return (x &gt;&gt; (p + 1 - n)) &amp; ~(~0 &lt;&lt; n); }   The idea is that, for the given number x, it will return the n bits starting at position p, counting from the right (with the farthest right bit being position 0). Given the following main() method:  int main(void) {     int x = 0xF994, p = 4, n = 3;     int z = getbits(x, p, n);     printf("getbits(%u (%x), %d, %d) = %u (%X)\n", x, x, p, n, z, z);      return 0; }   The output is:     getbits(63892 (f994), 4, 3) = 5 (5)   I get portions of this, but am having trouble with the "big picture," mostly because of the bits (no pun intended) that I don't understand.  The part I'm specifically having issues with is the complements piece: ~(~0 &lt;&lt; n). I think I get the first part, dealing with x; it's this part (and then the mask) that I'm struggling with -- and how it all comes together to actually retrieve those bits. (Which I've verified it is doing, both with code and checking my results using calc.exe -- thank God it has a binary view!)  Any help? Converting KML to shapefile without losing attributes using QGIS? Why does a bezier curve twist when rotated? If I create a bezier curve and rotate it in edit mode it does not accordingly rotate the tilt of the handles which creates an undesirable twisting along the curve.  Here is an example using a bezier circle with a square used for a bevel object:   Here it is after being rotated 90° about the y-axis:   How do I prevent/fix this? Is there a way to truly delete all deleted files? I know that on the windows operating system, when you delete a file it's still recoverable.  I'd like to avoid simply paving the harddrive with zeros as I would like to keep my OS installation as is, but is there a way to truly delete files that have been previously deleted? How do I clear command prompts in minecraft? 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It is also happening on the meta sites associated with the sites that have the problem.   For example, here is web apps meta site:    This a minor annoyance that has been around for at least a couple years. How to open nautilus without a desktop? I'm using xmonad, and I would like to open a nautilus window to a certain directory, because I like the convenience of browsing inside an encrypted zip file without unzipping it, which nautilus allows.   however, opening nautilus, even with a path argument starts a desktop on the monitor I'm using (There are 8 xmonad monitors) The desktop is inoperative and renders that monitor useless until nautilus is killed.  Is there any way to open just a nautilus window without any desktop starting? I currently have a 75% credit utilization, which I know is not favorable on about 35,000 revolving credit.  I am getting my year end bonus and plan on using that to completely pay off all of my credit cards leaving me with a 0% credit utilization.  Currently my credit score is 668, mostly due to my utilization, I pay everything on time, but just have too much debt, which is why i'm paying it all off.  My question is how much will paying off all my revolving credit and having a 0% utilization on 35,000 credit availability positively effect my credit score? Interpreting spline results I think that the question is contained in the title. Suppose we begin from something that is false for example $1=0$. Is it possible using only $\Rightarrow$ (and of course $\lnot ,\wedge,\lor$)  to prove any possible statement? It has been ages since i studied logic at the university so i would prefer a simple explanation (if possible) Is there a way of installing Ubuntu (Windows Subsystem for Linux) on Win10 (v1709) without using the Store? The Microsoft Store app is disabled by Group Policy by my university. I have administrator rights on my computer and I was wondering if there was a way of installing Windows Subsystem for Linux (WSL) directly? 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