Dart – Classes And Objects
Dart is an object-oriented programming language, so it supports the concept of class, object … etc. In Dart, we can define classes and objects of our own. We use the class keyword to do so. Dart supports object-oriented programming features like classes and interfaces.
Let us learn about Dart Classes and Objects in this article.
Classes in Dart
Class is the blueprint of objects and class is the collection of data members and data function means which include these fields, getter and setter, and constructor and functions.
Declaring class in Dart
class class_name {
// Body of class
}
In the above syntax:
- Class is the keyword used to initialize the class.
- class_name is the name of the class.
- The body of the class consists of fields, constructors, getter and setter methods, etc.
The body of Constructor includes three things: Class Fields, Class Methods, and Constructors.
1. Class Fields in Dart
Classes Fields are the variables which data for the objects. Let us check with an Example:
class Student{
// Fields defining the
// Properties of Class
int? roll_no;
String? name;
}
2. Class Methods in Dart
Class Methods are the functions that provide behavior for an object. Let us check with a Example:
class Student{
// Fields defining the
// Properties of Class
int? roll_no;
String? name;
void print_name(){
print("Student Name: $name");
}
}
A Constructor is a block of code that initializes the state and values during object creation. Constructor is name same as the class name and doesn’t return any value.
Syntax:
class_name( [ parameters ] ){
// Constructor Body
}
Objects in Dart
Objects are the instance of the class and they are declared by using a new keyword followed by the class name.
Syntax:
var object_name = new class_name([ arguments ]);
In the above syntax:
- new is the keyword use to declare the instance of the class
- object_name is the name of the object and its naming is similar to the variable name in dart.
- class_name is the name of the class whose instance variable is been created.
- arguments are the input which are needed to be pass if we are willing to call a constructor.
After the object is created, there will be the need to access the fields which we will create. We use the dot(.) operator for that purpose.
Syntax:
// For accessing the property
object_name.property_name;
// For accessing the method
object_name.method_name();
Creating a Class and Accessing its Fields
Example 1: Simple Example
// Creating Class named Gfg
class Gfg {
// Creating Field inside the class
String geek1 = '';
// Creating Function inside class
void geek()
{
print("Welcome to $geek1");
}
}
void main()
{
// Creating Instance of class
Gfg geek = new Gfg();
// Calling field name geek1 and assigning value
// to it using object of the class Gfg
geek.geek1 = 'w3wiki';
// Calling function name geek using object of the class Gfg
geek.geek();
}
Output:
Welcome to w3wiki
Explanation of the above Program:
Here we have first created the class named Gfg with a field geek1 and a function geek. Now in the main function, we have created an object of the class Gfg of name geek. Using this object we have assigned the value ‘w3wiki‘ to the string variable of the class and then we have called the geek function which has printed the output.
Example 2 :
class GFG {
String name = " ";
String get gfg1 {
return name;
}
void set gfg1(String name) {
this.name = name;
}
void result(){
print(name);
}
}
void main() {
GFG gfg2 = new GFG();
gfg2.name="Beginner for Beginner employee no 1 : avinash ,aakanksha";
gfg2.result();
}
Output:
Beginner for Beginner employee no 1 : avinash ,aakanksha