Contents
- 1. What are the ways to initialize data in a class when creating a class object?
- 2. The general form of the initialization of the internal data of a class using the direct assignment of the desired value
- 3. An example of initializing a single base type variable in a class
- 4. An example of initializing an array of variables of the base type in a class
- 5. Using an object’s initializer to initialize a class object in another class
- 6. Using object initializer to initialize an array of objects in a class
- 7. Using object initializer to initialize a structure variable in a class
- 8. An example of using an object initializer to initialize an array of structural variables
- 9. An example of initializing a variable and an array of variables of type enumeration (enum)
- 10. What requirements are imposed on the declaration of a class variable in the case of initialization of this variable by an object initializer?
- Related topics
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1. What are the ways to initialize data in a class when creating a class object?
In C#, a class object is created using the new operator. During creation, the internal data (variables) of a class can be initialized in one of the following ways:
- by assigning a class variable the desired value when it is declared (immediate initialization). This method is used only for variables of base types. If it is necessary to initialize a class object, then an object initializer is used;
- with the help of a class constructor;
- with the help of object initializer. This method is used for class objects or structure variables. In this case, the class data must be declared as public.
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2. The general form of the initialization of the internal data of a class using the direct assignment of the desired value
The internal data of a class can be initialized immediately upon their declaration with the help of a the following form:
type variable = value;
In this construct, a variable named variable of type type is initialized with value.
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3. An example of initializing a single base type variable in a class
The class Month is given, which implements the month of the year. The class declares one hidden variable ‘month’, which is initialized to 5 immediately upon declaration.
// class that implements the month of the yearclass Month{ // initialization of an internal variable when it is declared int month = 5; public int GetMonth() { return month; } public void SetMontgh(int _month) { month = _month; }}Using the object of class Month in other program code
Month mn = new Month();int t = mn.GetMonth(); // t = 5
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4. An example of initializing an array of variables of the base type in a class
Is demonstrated the initialization of an array of 5 double values, which is declared in the ArrayDouble5 class.
// class implements an array of 5 numbers of type doubleclass ArrayDouble5{ // array initialization when it is declared double[] A = { 3.5, 8.2, 1.6, 2.8, -0.0025 }; // access methods // get an array element public double GetAi(int index) { if ((index >= 0) && (index < 5)) return A[index]; return 0.0; } // write new value to array item public void SetAi(int index, double value) { if ((index >= 0) && (index < 5)) A[index] = value; }}Class usage may be as follows
// initialization the array in classArrayDouble5 ad = new ArrayDouble5();double val = ad.GetAi(3); // val = 2.8val = ad.GetAi(4); // val = -0.0025
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5. Using an object’s initializer to initialize a class object in another class
The initialization of class objects using object initializers is demonstrated. Three classes are given: Line, Triangle, Figures. In the Line class, public variables are declared that describe the coordinates of a segment on a plane. In the Triangle class, public variables are declared that define the coordinates of the points of the triangle.
In the Figures class, two objects (instances) of the Line and Triangle classes are declared. In the Figures class, objects of the Line and Triangle classes are initialized using object initializers.
// class that implements the line on the coordinate planeclass Line{ public int x1, y1, x2, y2;}// class that implements a triangle on the coordinate planeclass Triangle{ public int x1, y1, x2, y2, x3, y3;}// class that implements a figureclass Figures{ // class object initialization Line ln = new Line { x1 = 0, y1 = 3, x2 = 2, y2 = 5 }; Triangle tr = new Triangle { x1 = 1, y1 = 1, x2 = 4, y2 = 0, x3 = 2, y3 = 1 }; // access methods public Line GetLine() { return ln; } public Triangle GetTriangle() { return tr; }}The use of class Figures
Figures fg = new Figures();Line ln;Triangle tr;int t;ln = fg.GetLine();t = ln.x2; // t = 2t = ln.y1; // t = 3tr = fg.GetTriangle();t = tr.y2; // t = 0t = tr.x3; // t = 2
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6. Using object initializer to initialize an array of objects in a class
The example demonstrates initialization of an array of Worker objects in the Workers class. Initialization is done using an object initializer.
// class describing a workerclass Worker{ // It is required with public access modifier public string name; // the name of worker public int age; // age public double salary; // a salary of worker}// class in which an array of 3 Worker objects is declaredclass Workers{ public Worker[] wr = { new Worker { name = "Filippov F.F.", age = 35, salary = 70320.55 }, new Worker { name = "Johansonn S.", age = 37, salary = 66670.57 }, new Worker { name = "Gustaffson G.G.", age = 69, salary = 129380.55 } };}Important: in order to be able to initialize the Worker[] array in the Workers class, it is necessary that the data of the Worker class be declared with the public access modifier.
Using an array of wr objects can be as follows:
Workers W = new Workers();string name;int age;double salary;name = W.wr[1].name; // name = Johansonn S.age = W.wr[1].age; // age = 37salary = W.wr[1].salary; // salary = 66670.57
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7. Using object initializer to initialize a structure variable in a class
A Book structure that implements the book is declared. The CBook class demonstrates initialization of a structural variable of type Book. Initialization is possible only when a structural variable in a class is represented as a type-reference. This means that for a structured variable, memory is allocated by the operator new.
// structure that implements a bookstruct Book{ public string title; // title of book public string author; // name of author public int year; // year of issue public float price; // book cost}class CBook{ // initialization of a structure variable in a class as a reference type public Book b = new Book { title = "Tell the time 5+", author = "H. Cather", year = 2017, price = 110.00f };}Using a CBook object can be as follows:
// the object of class CBookCBook cb = new CBook();string ttl = cb.b.title; // ttl = "Tell the time 5+"
Important: in order to be able to initialize the object b of type Book in the CBook class, the structure fields (title, author, year, price) must be declared as public.
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8. An example of using an object initializer to initialize an array of structural variables
This example demonstrates how to declare and initialize an array of structures of type Book in the CBook class.
// structure implementing the bookstruct Book{ public string title; // title of book public string author; // name of author public int year; // year of issue public float price; // book cost}class Books{ // initialization of an array of structural variables in a class public Book[] B = { new Book { title = "Computer coding for kids", author = "Carol Vorderman", year = 2015, price = 320.00f }, new Book { title = "Math and English", author = "Paul Broadbent", year = 2015, price = 310.00f }, new Book { title = "Spelling 5+", author = "Hannah Catner", year = 2017, price = 0.00f } };}Using the object of the class Books in other program code
// object of class BooksBooks bk = new Books();string author = bk.B[2].author; // author = "Hannah Catner"
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9. An example of initializing a variable and an array of variables of type enumeration (enum)
A Months enumeration is specified that defines the months of the year. The example demonstrates:
- initialization of a variable of type enumeration Months in the class CMonths. Three variables (class data members) are initialized with the names mn1, mn2, mn3;
- initialization of an array of variables of type enumeration Months in the CMonths class.
// month of the yearenum Months{ Jan = 1, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec}// class in which internal variables of type 'enumeration' are initializedclass CMonths{ public Months mn1 = Months.Feb; public Months mn2 = Months.Jun; public Months mn3 = Months.Nov; // array of enumeration type variables Months[] array = { Months.Sep, Months.Jun, Months.Jan };}⇑
10. What requirements are imposed on the declaration of a class variable in the case of initialization of this variable by an object initializer?
To initialize a class variable using the object’s initializer, this variable must be declared as public with the ‘public’ access modifier. Otherwise, the compiler will generate the error message:
Variable is inaccessible due to its protection level
where variable – the name of the variable in the class to be initialized.
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Related topics
- Initializationof class data.Constructor.Constructor by default
- Dynamicmemory allocation. Operator‘new’. Memory allocation for value types, structures, enumerations, objects of classes.Memory allocation for arrays
- Classes.Class definition. Object of class. Keywordthis
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FAQs
In C#, a class object is created using the new operator. During creation, the internal data (variables) of a class can be initialized in one of the following ways: by assigning a class variable the desired value when it is declared (immediate initialization). This method is used only for variables of base types.
How to initialize object data type in C#? ›
C# Object Initializer
- using System;
- namespace CSharpFeatures.
- {
- class Student.
- {
- public int ID { get; set; }
- public string Name { get; set; }
- public string Email { get; set; }
To initialize a class member variable, put the initialization code in a static initialization block, as the following section shows. To initialize an instance member variable, put the initialization code in a constructor.
How do you initialize a class in a class? ›
There are two ways to initialize a class object:
- Using a parenthesized expression list. The compiler calls the constructor of the class using this list as the constructor's argument list.
- Using a single initialization value and the = operator.
Declaring (Creating) Variables
type variableName = value; Where type is a C# type (such as int or string ), and variableName is the name of the variable (such as x or name). The equal sign is used to assign values to the variable.
What is __ init __ method in class? ›
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.
Can we initialize variable in class in C#? ›
Class and Static Variables in C#
You can also initialize static variables inside the class definition.
How do you initialize a data type? ›
When you declare a variable, you should also initialize it. Two types of variable initialization exist: explicit and implicit. Variables are explicitly initialized if they are assigned a value in the declaration statement. Implicit initialization occurs when variables are assigned a value during processing.
How to initialize an array of objects in C#? ›
Initialize Arrays in C# with Known Number of Elements
We can initialize an array with its type and size: var students = new string[2]; var students = new string[2]; Here, we initialize and specify the size of the string array.
How many ways we can initialize the values to class variables? ›
You can initialize the instance variables of a class using final methods, constructors or, Instance initialization blocks.
You should always initialize native variables, especially if they are class member variables. Class variables, on the other hand, should have a constructor defined that will initialize its state properly, so you do not always have to initialize them.
Are class variables automatically initialized? ›
There is only one copy of a static variable, and initialization of that variable is executed just once, when the class is first loaded. If you don't provide any initial value for an instance variable, a default initial value is provided automatically.
How to initialize a class without constructor? ›
You need to construct an object and assign it to that space (eg. MyClass myclass = new MyClass(); ). The only way you can make an object is to construct it - so you can never initialize a class without a constructor.
How do you create an initialized object for this class? ›
Creating an Object
- Declaration − A variable declaration with a variable name with an object type.
- Instantiation − The 'new' keyword is used to create the object.
- Initialization − The 'new' keyword is followed by a call to a constructor. This call initializes the new object.
Show activity on this post. Object Initializers were something added to C# 3, in order to simplify construction of objects when you're using an object. Constructors run, given 0 or more parameters, and are used to create and initialize an object before the calling method gets the handle to the created object.
How to initialize multiple variables in C#? ›
In c#, we can declare and initialize multiple variables of the same data type in a single line by separating with a comma. Following is the example of defining the multiple variables of the same data type in a single line by separating with a comma in the c# programming language.
Does C# automatically initialize variables? ›
In C# for instance, fields, i.e. "variables" at the class level, are always automatically initialized to the default value for that variable type default(T) .
What is the proper way to declare and initialize a variable? ›
Rules to Declare and Initialize Variables
- Variable names must begin with a letter, underscore, non-number character. ...
- Few programming languages like PHP, Python, Perl, etc. ...
- Always use the '=' sign to initialize a value to the Variable.
- Do not use a comma with numbers.
__class__ is an attribute on the object that refers to the class from which the object was created. The above code creates an instance human_obj of the Human class.
Is __ init __ a constructor? ›
In Python, __init__ is a special method known as the constructor. It is automatically called when a new instance (object) of a class is created.
Differences between __new__ and __init__
__new__ is a static method, while __init__ is an instance method. __new__ is responsible for creating and returning a new instance, while __init__ is responsible for initializing the attributes of the newly created object.
What are the different types of variables in C#? ›
C# defines eight categories of variables: static variables, instance variables, array elements, value parameters, input parameters, reference parameters, output parameters, and local variables.
How to initialize a static class in C#? ›
Static classes cannot be instantiated. All the members of a static class must be static; otherwise the compiler will give an error. A static class can contain static variables, static methods, static properties, static operators, static events, and static constructors.
How to initialize a variable only once in C#? ›
How to initialize a Variable in C#? The Syntax for initializing a variable in C# is as follows: Syntax: data_type variable_name = value; Here, data_type is the type of data to be stored in the variable, variable_name is the name given to the variable and value is the initial value stored in the variable.
What are the 4 main data types? ›
4 Types of Data: Nominal, Ordinal, Discrete, Continuous.
Which method is used to initialize objects? ›
A constructor is a special method that has the same name as the class and is used to initialize attributes of a new object.
What are the ways to initialize set? ›
You can initialize a set by placing elements in between curly braces. Like other sequences, one set can have elements of multiple data-types. Moreover, you can also create a set from a list by using set() function.
Do you have to initialize an array in C#? ›
When you create an array, C# compiler implicitly initializes each array element to a default value depending on the array type. For example, for an int array all elements are initialized to 0.
How to create string array and initialize in C#? ›
String arrays can be created by using the following code: string[] firstString = new String[5]; Now, we declare and initialize a C# string array by adding values to it: string[] dessert = new string[] {"Cupcake","Cake","Candy"};
How to create array using array class in C#? ›
C# Arrays: Arrays of Class Types. To create a new application, on the main menu, click File -> New Project... To create a new class, in the Solution Explorer, right-click RenatlProperties1 -> Add -> Class...
There are three different types of variables a class can have in Java are local variables, instance variables, and class/static variables.
How many ways we can initialize an array? ›
There are two ways to specify initializers for arrays: With C89-style initializers, array elements must be initialized in subscript order. Using designated initializers, which allow you to specify the values of the subscript elements to be initialized, array elements can be initialized in any order.
In what all ways can we initialize instance variables of a class? ›
There are two alternatives to using a constructor to initialize instance variables: initializer blocks and final methods. The Java compiler copies initializer blocks into every constructor. Therefore, this approach can be used to share a block of code between multiple constructors.
Which type of variable Cannot be initialized inside class? ›
Note again that we cannot initialize a static member variable inside the class declaration.
Which method of a class is called to initialize an object of that class? ›
The constructor method is a special method of a class for creating and initializing an object instance of that class.
Which variables are automatically initialized? ›
There are three distinct types of variables that are automatically initialized with a default value based on their type.
- Static variables.
- Instance variables of class instances.
- Array elements.
- Reference type (a.k.a. pointer)
This refers to the process wherein a variable is assigned an initial value before it is used in the program. Without initialization, a variable would have an unknown value, which can lead to unpredictable outputs when used in computations or other operations.
Which class Cannot be initialized? ›
Abstract classes cannot be instantiated, but they can be subclassed.
Does every class need a constructor C#? ›
Unless the class is static, classes without constructors are given a public parameterless constructor by the C# compiler in order to enable class instantiation.
What happens if I create a class that doesn t contain a constructor? ›
You don't have to provide any constructors for your class, but you must be careful when doing this. The compiler automatically provides a no-argument, default constructor for any class without constructors. This default constructor will call the no-argument constructor of the superclass.
Is it possible to have a class without Constructor? If a class contains no instance constructor declarations, a default instance constructor is automatically provided. The only classes in C# which don't have any instance constructors are static classes, and they can't have constructors.
What is the order of initialization of constructors in C#? ›
While initialization starts with derived objects and moves down to the base object, the constructors initialize in reverse order, with the base constructor executing first, then the derived constructor.
What is initialization in C#? ›
init (C# Reference)
In C# 9 and later, the init keyword defines an accessor method in a property or indexer. An init-only setter assigns a value to the property or the indexer element only during object construction. This enforces immutability, so that once the object is initialized, it can't be changed again.
How to initialize a class property in C#? ›
C# Example with auto-initialize property
- using System;
- namespace CSharpFeatures.
- {
- public class PropertyInitializer.
- {
- public string Name { get; set; } = "Rahul Kumar";
- public static void Main(string[] args)
- {
__construct is a php magic method. It always exists and is called on object creation. init() is just a reguar method usually used in ZF..
What is the difference between private constructor and singleton in C#? ›
Private Constructors and Singleton Classes in C#
A singleton class has normal methods and you can call it using an instance. To prevent multiple instances of the class, the private constructor is used.
What is initialize method? ›
The initialize method is part of the object-creation process in Ruby & it allows you to set the initial values for an object. In other programming languages they call this a “constructor”.
What is method initialization? ›
The main purpose of the initialization method is to set up the initial hierarchy of the RODM data cache. Some functions can be used only by the initialization method. The RODM load function can be used as the RODM initialization method.
Which method is used to for initialization? ›
1 Answer. Best explanation: init-method is used to specify the initialization method.
What does it mean to initialize a class? ›
Initialization is the process of preparing an instance of a class, structure, or enumeration for use. This process involves setting an initial value for each stored property on that instance and performing any other setup or initialization that's required before the new instance is ready for use.
Two types of variable initialization exist: explicit and implicit. Variables are explicitly initialized if they are assigned a value in the declaration statement. Implicit initialization occurs when variables are assigned a value during processing.
What is initialization and examples? ›
In computer programming, initialization (or initialisation) is the assignment of an initial value for a data object or variable. The manner in which initialization is performed depends on the programming language, as well as the type, storage class, etc., of an object to be initialized.
How to initialize an object? ›
To create an object of a named class by using an object initializer
- Begin the declaration as if you planned to use a constructor. ...
- Type the keyword With , followed by an initialization list in braces. ...
- In the initialization list, include each property that you want to initialize and assign an initial value to it.
The way of initializing a variable is very similar to the use of PARAMETER attribute. More precisely, do the following to initial a variable with the value of an expression: add an equal sign (=) to the right of a variable name. to the right of the equal sign, write an expression.
What is the order of initialization? ›
Order of Initialization
In Java, the order for initialization statements is as follows: static variables and static initializers in order. instance variables and instance initializers in order. constructors.
Which method creates and initializes an object? ›
Instantiating an Object
The constructor method is responsible for initializing the new object.
Which command is used for initialize the variables? ›
Answer 4f1e8e4f0ae28d0001003eea
var is used to declare or initialize a variable.
What function is required for classes to initialize objects? ›
Constructor. The constructor method is a special method for creating and initializing an object created with a class.
Do you need to initialize a class? ›
Classes and objects in Java must be initialized before they are used.
How do you initialize an array of objects in a class? ›
One way to initialize the array of objects is by using the constructors. When you create actual objects, you can assign initial values to each of the objects by passing values to the constructor. You can also have a separate member method in a class that will assign data to the objects.
