A higher order function is a function that takes a function as a parameter or it returns a function. It allows us to write shorter and more beautiful code. Let‘s look at some examples.
fun <T> tryAndCatch(block: () -> T) = try {
block()
} catch (e: Exception) {
println(e.message)
}
This function will run code passed inside block variable inside try catch block and return result and also print exception in case it is thrown. What does it all mean?
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You already know that you can make templates for code snippets in Android Studio. You can do same thing for whole files as well. And you probably use file templates even if you didn‘t yet created your own.
Everytime you create new file using New menu, you are creating files based on file templates.
The main purpose of many classes is to hold data. But to effectively manipulative with data, we need to override quite a lot data. Class holding 3 String values would typically look something like this in Java:
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Unlike Java, Kotlin is purely object-oriented language. There are no primitives, everything is an object. With this said, you might be surprised by results.
Let’s compare two objects with equality operator:
object1 == object2
You expected to get false, right? But answer is true. Why? This code is translated to
a?.equals(b) ?: (b === null)
Java is not purely object-oriented programming language. We can use both objects and primitives for our variables. We can check easily if two primitives are same by identity operator ==. It is not as easy for objects.
Comparing objects with == is one of the frequented beginner’s mistakes. A beginner will check if two Strings with value “apple” are same and the answer is false. Because it doesn’t really check if objects are same but whether they point to the same memory address. How can you then check real equality of objects? Equals is the method you have to use.
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One of best programming practices is DRY. Don’t repeat yourself. And yet we often write similar blocks of code over and over again. And sometimes it really cannot be avoided. You can save yourself lot of time when you meet Android live and file templates. In this post, I write about live templates but I am sure I will come back to file templates later.
So how can you use live templates? Simply type template abbreviation, press Tab and block of code defined in template comes up. There are many live templates already included in Android Studio, but you can also define your own. To see them go to Editor, Settings and Live Templates. There they are, by default sorted by a programming language of their use. Looking like this.
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Kotlin helps you make your code shorter and more readable in many areas. One of them is constructors. In Java you have to tediously assign all variables passed to the constructor in similar style
this.something = something
If more constructors are required, you have to overload them and repeat yourself over and over. Like in the following example.
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I presume most Java programmers write some helper static methods and most probably even have some helper class including just these. So sooner or later you will need to write static methods like this in Kotlin.
public static float getPxFromDp(Context context, float dp) {
Resources r = context.getResources();
return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, r.getDisplayMetrics());
}
But you will find out you there is not anything like a static method in Kotlin. Fortunately, there are ways around this.
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There is a lot of ways how to learn Kotlin. Language reference, tutorials, video tutorials, online courses and much more. And now also Kotlin Edu.
Kotlin Educational Tools is Android Studio Plugin that helps you learn Kotlin by giving you small tasks. Read task description, write code and check. And if you cannot find the solution, you can click on Fill answer placeholders to get a right answer. Task description usually includes a link to Kotlin reference page, so you get right at the page with all you need to study to finish a task. It first looks like this.
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This is the first post on this blog. I will write mostly about Android programming. About things, I encounter that I find tricky or interesting. I might write about things I am currently studying and trying to make sense of. Because, after first few posts I have prepared, I can say writing about a problem is the best way how to understand it. There will be posts about Kotlin, Android Studio tips and tricks, Google tools, good (bad) old Java and other. Let’s start.