Tutorial by Examples: g

Pitfall - Overloading instead of overriding

Consider the following example: public final class Person { private final String firstName; private final String lastName; public Person(String firstName, String lastName) { this.firstName = (firstName == null) ? "" : firstName; this.lastName = (lastN...

Java Language • Java Pitfalls - Language syntax

Using .PHONY for non-files targets

Use .PHONY to specify the targets that are not files, e.g., clean or mrproper. Good example .PHONY: clean clean: rm *.o temp Bad example clean: rm *.o temp In the good example make knows that clean is not a file, therefore it will not search if it is or not up to date and will ex...

makefile • .PHONY target

Reading and writing data frames

Data frames are R's tabular data structure. They can be written to or read from in a variety of ways. This example illustrates a couple common situations. See the links at the end for other resources. Writing Before making the example data below, make sure you're in a folder you want to write to....

R Language • Input and output

Type erasing type erasure with std::any

This example uses C++14 and boost::any. In C++17 you can swap in std::any instead. The syntax we end up with is: const auto print = make_any_method<void(std::ostream&)>([](auto&& p, std::ostream& t){ t << p << "\n"; }); super_any<decltype(print...

C++ • Type Erasure

Drawing two rectangles on a

<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8" /> <title>Draw two rectangles on the canvas</title> <style> canvas{ border:1px solid gray; } </style> <script async...

HTML • Canvas

Adding dependencies using task names

We can change the tasks execution order with the dependsOn method. task A << { println 'Hello from A' } task B(dependsOn: A) << { println "Hello from B" } Adding `dependsOn: causes: task B depends on task A Gradle to execute A task everytime before the B ta...

gradle • Task dependencies

Adding dependencies from another project

project('projectA') { task A(dependsOn: ':projectB:B') << { println 'Hello from A' } } project('projectB') { task B << { println 'Hello from B' } } To refer to a task in another project, you prefix the name of the task with the path of the pr...

gradle • Task dependencies

Adding dependency using task object

task A << { println 'Hello from A' } task B << { println 'Hello from B' } B.dependsOn A It is an alternative way to define the dependency instead of using the task name. And the output is the same: > gradle -q B Hello from A Hello from B

gradle • Task dependencies

Adding multiple dependencies

You can add multiple dependencies. task A << { println 'Hello from A' } task B << { println 'Hello from B' } task C << { println 'Hello from C' } task D << { println 'Hello from D' } Now you can define a set of dependencies: B.dependsOn A...

gradle • Task dependencies

Exporting .csv files

Exporting using base R Data can be written to a CSV file using write.csv(): write.csv(mtcars, "mtcars.csv") Commonly-specified parameters include row.names = FALSE and na = "". Exporting using packages readr::write_csv is significantly faster than write.csv and does not ...

R Language • Reading and writing tabular data in plain-text files (CSV, TSV, etc.)

Draw behind existing shapes with "destination-over"

context.globalCompositeOperation = "destination-over" "destination-over" compositing places new drawing under existing drawings. context.drawImage(rainy,0,0); context.globalCompositeOperation='destination-over'; // sunny UNDER rainy context.drawImage(sunny,0,0);

html5-canvas • Compositing

Erase existing shapes with "destination-out"

context.globalCompositeOperation = "destination-out" "destination-out" compositing uses new shapes to erase existing drawings. The new shape is not actually drawn -- it is just used as a "cookie-cutter" to erase existing pixels. context.drawImage(apple,0,0); conte...

html5-canvas • Compositing

Default compositing: New shapes are drawn over Existing shapes

context.globalCompositeOperation = "source-over" "source-over" compositing [default], places all new drawings over any existing drawings. context.globalCompositeOperation='source-over'; // the default context.drawImage(background,0,0); context.drawImage(parachuter,0,0); ...

html5-canvas • Compositing

Clip images inside shapes with "destination-in"

context.globalCompositeOperation = "destination-in" "destination-in" compositing clips existing drawings inside a new shape. Note: Any part of the existing drawing that falls outside the new drawing is erased. context.drawImage(picture,0,0); context.globalCompositeOperation...

html5-canvas • Compositing

Clip images inside shapes with "source-in"

context.globalCompositeOperation = "source-in"; source-in compositing clips new drawings inside an existing shape. Note: Any part of the new drawing that falls outside the existing drawing is erased. context.drawImage(oval,0,0); context.globalCompositeOperation='source-in'; // pictu...

html5-canvas • Compositing

Detect errors when writing a value on Android

There are many reasons a write operation may fail. A frequent one is because your security rules reject the operation, for example because you're not authenticated (by default a database can only be accessed by an authenticated user). You can see these security rule violations in the logcat output....

firebase • How do I listen for errors when accessing the database?

Ordering with the mustRunAfter method

task A << { println 'Hello from A' } task B << { println 'Hello from B' } B.mustRunAfter A The B.mustRunAfter A line tells Gradle to run task after task specified as an argument. And the output is: > gradle -q B A Hello from A Hello from B The ordering rule d...

gradle • Ordering tasks

Adding a ViewPager

Make sure the following dependency is added to your app's build.gradle file under dependencies: compile 'com.android.support:support-core-ui:25.3.0' Then add the ViewPager to your activity layout: <android.support.v4.view.ViewPager android:id="@+id/viewpager" android:layo...

Android • ViewPager

Using Resolvers and Guards

We're using a toplevel guard in our route config to catch the current user on first page load, and a resolver to store the value of the currentUser, which is our authenticated user from the backend. A simplified version of our implementation looks as follows: Here is our top level route: export c...

Angular 2 • Routing (3.0.0+)

Customizing the CardView

CardView provides a default elevation and corner radius so that cards have a consistent appearance across the platforms. You can customize these default values using these attributes in the xml file: card_view:cardElevation attribute add elevation in CardView. card_view:cardBackgroundColor attr...

Android • CardView