Full Answer
What is the difference between init block and primary constructor?
The primary constructor cannot contain any code. init blocks allow adding code to the primary constructor. A class in Kotlin class a primary constructor (the one after a class name) which does not contain code, it is only able to initialize properties (e.g. class X (var prop: String) ).
What is a constructor in Kotlin?
Constructor is a block of code which get initialised when the object is created. In Java, the constructor has the same name as of the class. But in Kotlin we have something different for constructors i.e Primary and Secondary constructors. You can read more about them here.
How to add a value to a variable using init block?
Value "T" is assigned to s from the primary constructor of Sample class, and then immediately init block starts to execute it will add "B" to the variable. After init block secondary constructor block starts to execute and s will become "TBU". The primary constructor cannot contain any code. init blocks allow adding code to the primary constructor.
How to place initializer code in initializer blocks?
Initialization code can be placed in initializer blocks, which are prefixed with the init keyword. During an instance initialization, the initializer blocks are executed in the same order as they appear in the class body, interleaved with the property initializers:...
What does init block do in Kotlin?
Kotlin init The code inside the init block is the first to be executed when the class is instantiated. The init block is run every time the class is instantiated, with any kind of constructor as we shall see next. Multiple initializer blocks can be written in a class. They'll be executed sequentially as shown below.
What is the init block?
The initializer block contains the code that is always executed whenever an instance is created and it runs each time when an object of the class is created. There are 3 areas where we can use the initializer blocks: Constructors. Methods. Blocks.
What is init function in Android?
The init{.. } block in the place, where you can put more code that will run after properties are initialized: initializer blocks are executed in the same order as they appear in the class body, interleaved with the property initializers.
What is initialization in Kotlin?
Using Class Constructor The standard way to initialize an object in Kotlin is with the class constructor. It can accept a set of parameters to initialize its fields, or it can be parameterless. Kotlin has a concise syntax for declaring properties and initializing them: 1.
What is primary constructor in Kotlin?
The Kotlin primary constructor initializes the class, whereas the secondary constructor helps to include some extra logic while initializing the class.
What is init () method in Java?
Init method is a predefined method to initialize an object after its creation. Init method is a life cycle method for servlets for java. It is started by the browser when java program is loaded and run by the browser. Init method is a predefine method to initialize an object after its creation.
What is the purpose of the Init method?
The __init__ method is the Python equivalent of the C++ constructor in an object-oriented approach. The __init__ function is called every time an object is created from a class. The __init__ method lets the class initialize the object's attributes and serves no other purpose. It is only used within classes.
What is the difference between INIT and constructor?
difference work of between init() and constructor? The constructor is called by the container simply to create a POJO (plain old java object). init method is the method which is invoked when servlet in called and it adds values to the servlet context so its a very much difference between constructor and init method...
What is abstract class in Kotlin?
A Kotlin abstract class is similar to Java abstract class which can not be instantiated. This means we cannot create objects of an abstract class. However, we can inherit subclasses from a Kotlin abstract class. A Kotlin abstract class is declared using the abstract keyword in front of class name.
What is lazy keyword in Kotlin?
Lazy is mainly used when you want to access some read-only property because the same object is accessed throughout. That's it for this blog.
Is lazy thread safe in Kotlin?
It is lazy and thread-safe, it initializes upon first call, much as Java's static initializers. You can declare an object at top level or inside a class or another object.
How Kotlin is null safe?
Kotlin has a safe call operator (?.) to handle null references. This operator executes any action only when the reference has a non-null value. Otherwise, it returns a null value. The safe call operator combines a null check along with a method call in a single expression.
What is the block in Java?
A block in Java is a set of code enclosed within curly braces { } within any class, method, or constructor. It begins with an opening brace ( { ) and ends with an closing braces ( } ). Between the opening and closing braces, we can write codes which may be a group of one or more statements.
What is a instance block in Java?
Instance initializer block works are used to initialize the properties of an object. It is invoked before the constructor is invoked. It is invoked every time an object is created.
What are Initializers?
The initializer list is used to directly initialize data members of a class. An initializer list starts after the constructor name and its parameters.
When init block get executed in Perl?
BEGIN, UNITCHECK, CHECK, INIT and END. Five specially named code blocks are executed at the beginning and at the end of a running Perl program.
How Kotlin init Work?
The kotlin init is the block which can be placed for the initialization codes the prefixed with the init keyword. During the initialization of an instance, the initializer blocks are to be executed in the same order and they appear in the class body which is interleaved with the property initializers.
Conclusion
In kotlin language we used different concepts to implement the application like that init is one of the block types and it is mainly used to store and execute the datas. Every time the class is instantiated the init block is executed with any kind of constructors with sequential order.
Recommended Articles
This is a guide to Kotlin init. Here we discuss the introduction, how Kotlin init work? and examples for better understanding. You may also have a look at the following articles to learn more –
What is an init block?
init blocks allow adding code to the primary constructor. The primary constructor cannot contain any code. Initialization code can be placed in initializer blocks, which are prefixed with the init keyword.
What is a class in Kotlin?
A class in Kotlin class a primary constructor (the one after a class name) which does not contain code, it is only able to initialize properties (e.g. class X (var prop: String) ). The init {..} block in the place, where you can put more code that will run after properties are initialized:
What happens to the initializer block after the primary constructor?
The init block will execute immediately after the primary constructor. Initializer blocks effectively become part of the primary constructor. The constructor is the secondary constructor. Delegation to the primary constructor happens as the first statement of a secondary constructor, so the code in all initializer blocks is executed before the secondary constructor body.
Where is initialization code placed?
Initialization code can be placed in initializer blocks, which are prefixed with the init keyword. During an instance initialization, the initializer blocks are executed in the same order as they appear in the class body, interleaved with the property initializers: ...
Does init block contain code?
Thus the init {..} in invoked after primary constructor but before a secondary one. The primary constructor cannot contain any code. init blocks allow adding code to the primary constructor. The primary constructor cannot contain any code.
Is the initializer a primary constructor?
Initializer blocks effectively become part of the primary constructor. The constructor is the secondary constructor. Delegation to the primary constructor happens as the first statement of a secondary constructor, so the code in all initializer blocks is executed before the secondary constructor body.
Why is the bytecode truncated in Kotlin?
The remaining part of the bytecode is truncated for the sake of brevity. Anyway, it’s obvious that Kotlin compiles the primary constructor to hold all the logic.
What happens to init blocks and property initializers?
Put simply, the init blocks and property initializers will end up as part of the primary constructor. Obviously, we can verify this by taking a look at the generated bytecode:
What is the first part of bytecode?
This is a highly truncated and simplified version of the bytecode! As shown above, the first part of the bytecode is initializing the firstName and lastName constructor properties. After that, the bytecode is dedicated to the fullName property initializer and printing the static log. And finally, we have a set of opcodes responsible for the first init block.
Can a primary constructor contain code?
As opposed to secondary constructors, the primary constructor can’t contain any code. To overcome this limitation, we can put initialization logic inside init blocks and property initializers, as we did in the above example.
Can you put code in a constructor in Kotlin?
Even though we can’t put some code in primary constructors in Kotlin, the generated bytecode for the constructor will contain all the initialization logic. Basically, the Kotlin compiler will generate a big constructor containing the logic from all the property initializers and init block initializers.