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What is polymorphism, what is it for, and how is it used?
...erate on different data types.
The classic example is the Shape class and all the classes that can inherit from it (square, circle, dodecahedron, irregular polygon, splat and so on).
With polymorphism, each of these classes will have different underlying data. A point shape needs only two co-ordin...
Maven error “Failure to transfer…”
...
Remove all your failed downloads:
find ~/.m2 -name "*.lastUpdated" -exec grep -q "Could not transfer" {} \; -print -exec rm {} \;
For windows:
cd %userprofile%\.m2\repository
for /r %i in (*.lastUpdated) do del %i
Then rightc...
When to use RSpec let()?
...sn't use any of the instance variables defined in the hook. This isn't usually a big deal, but if the setup of the instance variable takes a long time, then you're wasting cycles. For the method defined by let, the initialization code only runs if the example calls it.
You can refactor from a loca...
Checkstyle vs. PMD
...lso able to point out questionable coding practices and its output is generally more relevant and useful.
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How to permanently disable region-folding in Visual Studio 2008
... folding in visual studio 2008? Some of my colleagues love it, but I personally always want to see all the code, and never want code folded out of sight. I'd like a setting that means my copy of Visual Studio never folds #regions or function bodies.
...
How do I get SUM function in MySQL to return '0' if no values are found?
...iddle.com/#!2/d1542/3/0
More Information:
Given three tables (one with all numbers, one with all nulls, and one with a mixture):
SQL Fiddle
MySQL 5.5.32 Schema Setup:
CREATE TABLE foo
(
id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
val INT
);
INSERT INTO foo (val) VALUES
(null),(1),(n...
Execute command on all files in a directory
...rovide the code to do the following:
Assume there is a directory of files, all of which need to be run through a program. The program outputs the results to standard out. I need a script that will go into a directory, execute the command on each file, and concat the output into one big output file.
...
How to truncate a foreign key constrained table?
...ata integrity.
Option 1:
Remove constraints
Perform TRUNCATE
Delete manually the rows that now have references to nowhere
Create constraints
Option 2: suggested by user447951 in their answer
SET FOREIGN_KEY_CHECKS = 0;
TRUNCATE table $table_name;
SET FOREIGN_KEY_CHECKS = 1;
...
When should one use final for method parameters and local variables?
...e set by end of construction, making that field reference immutable. This allows safe publication of fields and can avoid the need for synchronization on later reads. (Note that for an object reference, only the field reference is immutable - things that object reference refers to can still change...
Rails ActiveRecord date between
...
I would personally created a scope to make it more readable and re-usable:
In you Comment.rb, you can define a scope:
scope :created_between, lambda {|start_date, end_date| where("created_at >= ? AND created_at <= ?", start_date, e...