All Questions
24,196,085
questions
4321
votes
35
answers
1.8m
views
What are the differences between a HashMap and a Hashtable in Java?
What are the differences between a HashMap and a Hashtable in Java?
Which is more efficient for non-threaded applications?
- 51.9k
4283
votes
40
answers
5.4m
views
How do I UPDATE from a SELECT in SQL Server?
In SQL Server, it is possible to insert rows into a table with an INSERT.. SELECT statement:
INSERT INTO Table (col1, col2, col3)
SELECT col1, col2, col3
FROM other_table
WHERE sql = 'cool'
Is it ...
- 45.1k
4274
votes
34
answers
3.5m
views
How to insert an item into an array at a specific index?
I am looking for a JavaScript array insert method, in the style of:
arr.insert(index, item)
Preferably in jQuery, but any JavaScript implementation will do at this point.
- 83.7k
4229
votes
1
answer
3.2m
views
The Definitive C++ Book Guide and List
This question attempts to collect the few pearls among the dozens of bad C++ books that are published every year.
Unlike many other programming languages, which are often picked up on the go from ...
4227
votes
33
answers
3.6m
views
Is there a CSS parent selector?
How do I select the <li> element that is a direct parent of the anchor element?
As an example, my CSS would be something like this:
li < a.active {
property: value;
}
Obviously there are ...
- 57.7k
4218
votes
94
answers
4.6m
views
How to round to at most 2 decimal places, if necessary
I'd like to round at most two decimal places, but only if necessary.
Input:
10
1.7777777
9.1
Output:
10
1.78
9.1
How can I do this in JavaScript?
- 45k
4199
votes
38
answers
440k
views
How can I pair socks from a pile efficiently?
Yesterday I was pairing the socks from the clean laundry and figured out the way I was doing it is not very efficient. I was doing a naive search — picking one sock and "iterating" the pile in ...
- 178k
4196
votes
78
answers
2.6m
views
How can I validate an email address using a regular expression?
Over the years I have slowly developed a regular expression that validates most email addresses correctly, assuming they don't use an IP address as the server part.
I use it in several PHP programs, ...
4191
votes
35
answers
1.7m
views
4169
votes
36
answers
946k
views
What is the !! (not not) operator in JavaScript?
I saw this code:
this.vertical = vertical !== undefined ? !!vertical : this.vertical;
It seems to be using !! as an operator, which I don't recognize. What does it do?
- 44.5k
4157
votes
61
answers
3.4m
views
Sort array of objects by string property value
I have an array of JavaScript objects:
var objs = [
{ first_nom: 'Laszlo', last_nom: 'Jamf' },
{ first_nom: 'Pig', last_nom: 'Bodine' },
{ first_nom: 'Pirate', last_nom: '...
- 41.9k
4148
votes
142
answers
4.7m
views
Message 'src refspec master does not match any' when pushing commits in Git
I clone my repository with:
git clone ssh://xxxxx/xx.git
But after I change some files and add and commit them, I want to push them to the server:
git add xxx.php
git commit -m "TEST"
git push ...
- 41.9k
4132
votes
13
answers
1.5m
views
grep: show lines surrounding each match [closed]
How do I grep and show the preceding and following 5 lines surrounding each matched line?
- 302k
4130
votes
54
answers
3.4m
views
How do I get the current branch name in Git?
How do I get the name of the current branch in Git?
- 48.5k
4119
votes
34
answers
7.5m
views
How can I iterate over rows in a Pandas DataFrame?
I have a pandas dataframe, df:
c1 c2
0 10 100
1 11 110
2 12 120
How do I iterate over the rows of this dataframe? For every row, I want to access its elements (values in cells) by the name ...
- 129k
4107
votes
42
answers
1.9m
views
Create ArrayList from array
Element[] array = {new Element(1), new Element(2), new Element(3)};
How do I convert the above variable of type Element[] into a variable of type ArrayList<Element>?
ArrayList<Element> ...
- 54.3k
4107
votes
59
answers
5.2m
views
How do I generate random integers within a specific range in Java?
How do I generate a random int value in a specific range?
The following methods have bugs related to integer overflow:
randomNum = minimum + (int)(Math.random() * maximum);
// Bug: `randomNum` can be ...
- 49.4k
4080
votes
33
answers
3.7m
views
Checking if a key exists in a JavaScript object?
How do I check if a particular key exists in a JavaScript object or array?
If a key doesn't exist, and I try to access it, will it return false? Or throw an error?
- 53.6k
4077
votes
7
answers
4.9m
views
How do I clone a specific Git branch? [duplicate]
Git clone will clone remote branch into local.
Is there any way to clone a specific branch by myself without switching branches on the remote repository?
- 43.6k
4058
votes
23
answers
1.8m
views
Make an existing Git branch track a remote branch?
I know how to make a new branch that tracks remote branches, but how do I make an existing branch track a remote branch?
I know I can just edit the .git/config file, but it seems there should be an ...
- 212k
4054
votes
55
answers
5.6m
views
How do I check for an empty/undefined/null string in JavaScript?
Is there a string.Empty in JavaScript, or is it just a case of checking for ""?
- 69.1k
4039
votes
46
answers
5.4m
views
Loop through an array in JavaScript
In Java, you can use a for loop to traverse objects in an array as follows:
String[] myStringArray = {"Hello", "World"};
for (String s : myStringArray) {
// Do something
}
Can ...
- 57.7k
4030
votes
12
answers
369k
views
Proper use cases for Android UserManager.isUserAGoat()?
I was looking at the new APIs introduced in Android 4.2.
While looking at the UserManager class I came across the following method:
public boolean isUserAGoat()
Used to determine whether the ...
- 72.2k
4027
votes
21
answers
3.1m
views
How do I tell if a file does not exist in Bash?
This checks if a file exists:
#!/bin/bash
FILE=$1
if [ -f $FILE ]; then
echo "File $FILE exists."
else
echo "File $FILE does not exist."
fi
How do I only check if the ...
- 403k
3989
votes
46
answers
3.4m
views
How do I efficiently iterate over each entry in a Java Map?
If I have an object implementing the Map interface in Java and I wish to iterate over every pair contained within it, what is the most efficient way of going through the map?
Will the ordering of ...
- 38.9k
3982
votes
27
answers
4.1m
views
How to use a global variable in a function?
How do I create or use a global variable inside a function?
How do I use a global variable that was defined in one function inside other functions?
Failing to use the global keyword where appropriate ...
- 157k
3967
votes
36
answers
587k
views
Is floating-point math broken?
Consider the following code:
0.1 + 0.2 == 0.3 -> false
0.1 + 0.2 -> 0.30000000000000004
Why do these inaccuracies happen?
- 45.2k
3950
votes
14
answers
1.1m
views
Move existing, uncommitted work to a new branch in Git
I started some work on a new feature and after coding for a bit, I decided this feature should be on its own branch.
How do I move the existing uncommitted changes to a new branch and reset my ...
- 76.7k
3924
votes
15
answers
1.2m
views
Remove a file from a Git repository without deleting it from the local filesystem
I want to remove a file from my repository.
git rm file_to_remove.txt
will remove the file from the repository, but it will also remove the file from the local file system. How do I remove this file ...
- 40.1k
3920
votes
44
answers
1.3m
views
What are the differences between a pointer variable and a reference variable?
What is the difference between a pointer variable and a reference variable?
- 59.5k
3910
votes
32
answers
2.1m
views
3902
votes
27
answers
2.5m
views
View the change history of a file using Git versioning
How do I view the history of an individual file with complete details of what has changed?
git log -- [filename] shows me the commit history of a file, but how do I see the file content that changed?
- 40.5k
3897
votes
54
answers
4.4m
views
3890
votes
41
answers
4.3m
views
How do I test for an empty JavaScript object?
After an AJAX request, sometimes my application may return an empty object, like:
var a = {};
How can I check whether that's the case?
- 39.3k
3858
votes
6
answers
1.5m
views
How to catch multiple exceptions in one line? (in the "except" block)
I know that I can do:
try:
# do something that may fail
except:
# do this if ANYTHING goes wrong
I can also do this:
try:
# do something that may fail
except IDontLikeYouException:
# ...
- 113k
3856
votes
11
answers
318k
views
Why don't Java's +=, -=, *=, /= compound assignment operators require casting?
Until today, I thought that for example:
i += j;
Was just a shortcut for:
i = i + j;
But if we try this:
int i = 5;
long j = 8;
Then i = i + j; will not compile but i += j; will compile fine.
...
- 37.6k
3850
votes
17
answers
519k
views
Why is char[] preferred over String for passwords?
In Swing, the password field has a getPassword() (returns char[]) method instead of the usual getText() (returns String) method. Similarly, I have come across a suggestion not to use String to handle ...
- 39.5k
3832
votes
21
answers
3.8m
views
3830
votes
31
answers
4.3m
views
How do I POST JSON data with cURL?
I use Ubuntu and installed cURL on it. I want to test my Spring REST application with cURL. I wrote my POST code at the Java side. However, I want to test it with cURL. I am trying to post a JSON data....
- 74.3k
3825
votes
96
answers
5.0m
views
What is the JavaScript version of sleep()?
Is there a better way to engineer a sleep in JavaScript than the following pausecomp function (taken from here)?
function pausecomp(millis)
{
var date = new Date();
var curDate = null;
do ...
3792
votes
14
answers
2.5m
views
3785
votes
23
answers
5.1m
views
Convert bytes to a string in Python 3
I captured the standard output of an external program into a bytes object:
>>> from subprocess import *
>>> stdout = Popen(['ls', '-l'], stdout=PIPE).communicate()[0]
>>> ...
- 43.8k
3783
votes
33
answers
1.3m
views
How do I stash only one file out of multiple files that have changed?
How do I stash only one of the multiple changed files on my branch?
- 102k
3778
votes
26
answers
3.8m
views
Get the current URL with JavaScript?
All I want is to get the website URL. Not the URL as taken from a link. On the page loading I need to be able to grab the full, current URL of the website and set it as a variable to do with as I ...
dougoftheabaci
3770
votes
7
answers
4.5m
views
Iterate through a HashMap [duplicate]
What's the best way to iterate over the items in a HashMap?
- 57.8k
3764
votes
82
answers
2.4m
views
How do I correctly clone a JavaScript object?
I have an object x. I'd like to copy it as object y, such that changes to y do not modify x. I realized that copying objects derived from built-in JavaScript objects will result in extra, unwanted ...
- 39.9k
3735
votes
61
answers
754k
views
How can I create a memory leak in Java?
I just had an interview where I was asked to create a memory leak with Java.
Needless to say, I felt pretty dumb, having no idea how to start creating one.
What would an example be?
3724
votes
28
answers
1.0m
views
What is the difference between __str__ and __repr__?
What is the difference between __str__ and __repr__ in Python?
- 117k
3720
votes
26
answers
3.0m
views
How do I create a remote Git branch?
I created a local branch. How do I push it to the remote server?
UPDATE: I have written a simpler answer for Git 2.0 here.
- 110k
3711
votes
32
answers
3.1m
views
Git refusing to merge unrelated histories on rebase
During git rebase origin/development the following error message is shown from Git:
fatal: refusing to merge unrelated histories
Error redoing merge 1234deadbeef1234deadbeef
My Git version is 2.9.0. ...
