How can I determine if a variable is ‘undefined’ or ‘null’?
You can use the qualities of the abstract equality operator to do this: Because null == undefined is true, the above code will catch both null and undefined.
variables
Java, “Variable name” cannot be resolved to a variable
If you look at the scope of the variable ‘hoursWorked’ you will see that it is a member of the class (declared as private int) The two variables you are having trouble with are passed as parameters to the constructor. The error message is because ‘hours’ is out of scope in the setter.
How to trim whitespace from a Bash variable?
A simple answer is: Xargs will do the trimming for you. It’s one command/program, no parameters, returns the trimmed string, easy as that! Note: this doesn’t remove all internal spaces so “foo bar” stays the same; it does NOT become “foobar”. However, multiple spaces will be condensed to single spaces, so “foo bar” will become “foo bar”. In addition it doesn’t remove … Read more
Error: “Cannot modify the return value” c#
This is because Point is a value type (struct). Because of this, when you access the Origin property you’re accessing a copy of the value held by the class, not the value itself as you would with a reference type (class), so if you set the X property on it then you’re setting the property on the copy and then discarding it, leaving … Read more
How to check if a variable is set in Bash?
(Usually) The right way where ${var+x} is a parameter expansion which evaluates to nothing if var is unset, and substitutes the string x otherwise. Quotes Digression Quotes can be omitted (so we can say ${var+x} instead of “${var+x}”) because this syntax & usage guarantees this will only expand to something that does not require quotes (since it either expands to x (which contains no word breaks so it … Read more
Append integer to beginning of list in Python
How it works: array.insert(index, value) Insert an item at a given position. The first argument is the index of the element before which to insert, so array.insert(0, x) inserts at the front of the list, and array.insert(len(array), x) is equivalent to array.append(x).Negative values are treated as being relative to the end of the array.
“No X11 DISPLAY variable” – what does it mean?
If you’re on the main display, then or if you’re using csh or tcsh before running your app. Actually, I’m surprised it isn’t set automatically. Are you trying to start this application from a non-graphic terminal? If not, have you modified the default .profile, .login, .bashrc or .cshrc? Note that setting the DISPLAY to :0.0 … Read more
How do you check if a variable is an array in JavaScript?
There are several ways of checking if an variable is an array or not. The best solution is the one you have chosen. This is the fastest method on Chrome, and most likely all other browsers. All arrays are objects, so checking the constructor property is a fast process for JavaScript engines. If you are … Read more
Non-static variable cannot be referenced from a static context
You must understand the difference between a class and an instance of that class. If you see a car on the street, you know immediately that it’s a car even if you can’t see which model or type. This is because you compare what you see with the class “car”. The class contains which is similar to … Read more
Non-static variable cannot be referenced from a static context
You must understand the difference between a class and an instance of that class. If you see a car on the street, you know immediately that it’s a car even if you can’t see which model or type. This is because you compare what you see with the class “car”. The class contains which is similar to … Read more