Classes and Methods
Class
A class is an abstract blueprint used to create more specific, concrete objects.
Object
Objects are instances of classes created with specific data.
1
2
3
4
5
6
7
8
9
10
class Person {
void sayHi() {
print('Hi');
}
}
void call() {
final person = Person();
person.sayHi();
}
Conditional Property Access
In order to guard access to a property or method of an object that might be null.
?. Add a question mark before the dot.
1
2
3
4
5
List<String>? names = ['Jeremy'];
List<String>? nulls = null;
print(names?.length ?? 0); // prints 1
print(nulls?.length ?? 0); // prints 0
Constructors
Constructor is a member function of a class that has the same name as the class name. It helps to initialize the object of a class.
Factory Constructors can return instances that are not of the same class.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
class Person {
final String name;
// constructor
Person(this.name);
// factory constructor
factory Person.createHuman() {
return Person('Default');
}
void printName() {
print(name);
}
}
void call() {
final person = Person.createHuman();
person.printName();
}
Operators
Custom Operators
We can define custom operators on your own classes.
Overriding the == operator
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
class Person {
final String name;
// constructor
Person(this.name);
@override
// covariant force class to ignore type of parameters defined in super class
bool operator ==(covariant Person other) => other.name == name;
@override
// hashCode is the identifier for instances of the class
int get hashCode => name.hashCode;
}
void call() {
final person1 = Person('John');
final person2 = Person('John');
print(person1 == person2); // prints true
}
Null Aware Operators
Null aware operators are used to add null aware objects. They are listed below:
? Add a question mark after the data type to make it nullable.
1
String? name = null;
?? is used to find the first non-null value.
1
2
3
4
5
6
String? value1 = null;
String? value2 = 'A';
String? value3 = 'B';
print(value1 ?? value3 ?? value2); // prints B
print(value2 ?? value1 ?? value3); // prints A
??= is used to assign value to a variable only if the variable is currently null.
1
2
3
4
5
6
int? number = null;
number ??= 5;
print(number); // prints 5
number ??= 10;
print(number); // still prints 5
References
- https://dart.dev/guides