Dart Basic- Libraries

What is a programming library?

A programming library is a collection of prewritten code that programmers can use to optimize tasks. Dart has a set of built-in libraries that are useful to store routines that are frequently used. A Dart library comprises of a set of classes, constants, functions, typedefs, properties, and exceptions.

Importing a Library

Importing a library means the library is available to the calling code. Multiple import statements are continued in a dart file.

The syntax for importing a library in Dart is given below −

import 'URI'

Some commonly used libraries are given below −

Example : Importing and using a Library

import 'dart:math'; 
void main() { 
   print("Square root of 25 is: ${sqrt(25)}"); 
}

Output

Square root of 36 is: 5.0

Example:

import 'dart:io';
import 'dart:math';
import 'dart:convert';
import 'dart:typed_data';

void main() {
  // Read a file and print its contents
  final file = File('example.txt');
  final contents = file.readAsStringSync();
  print(contents);
  
  // Generate a random number between 0 and 99
  final random = Random();
  final number = random.nextInt(100);
  print('Random number: $number');
  
  // Convert a map to JSON and back
  final map = {'name': 'John', 'age': 30};
  final json = jsonEncode(map);
  print(json);
  final decoded = jsonDecode(json);
  print(decoded);
  
  // Create a typed list of integers and sum its values
  final list = Int32List.fromList([1, 2, 3]);
  final sum = list.fold(0, (a, b) => a + b);
  print('Sum: $sum');
}

In this example, we use the dart:io library to read a file from the filesystem and print its contents. We also use the dart:math library to generate a random number between 0 and 99.

We use the dart:convert library to convert a map to JSON format and back again. This is a common task when working with web APIs that send and receive JSON data.

Finally, we use the dart:typed_data library to create a typed list of integers and sum its values. The typed list is more memory-efficient than a regular list because it can store fixed-size values without any overhead.

Encapsulation in Libraries

Encapsulation in Dart happens at the library level instead of the class level, unlike other object-oriented programming languages. Dart provides the facility to encapsulate or restrict access to the content of the Dart library. It can be done by using the _(underscore), followed by the identifier. The underscore (_)) symbol makes the library’s content completely private.

Creating Custom Libraries

Dart also allows you to use your own code as a library. An example of a Custom Library is given below:

library calculator_lib;  
import 'dart:math'; 

//import statement after the libaray statement  
int add(int firstNumber,int secondNumber){ 
   print("inside add method of Calculator Library ") ; 
   return firstNumber+secondNumber; 
}  
int modulus(int firstNumber,int secondNumber){ 
   print("inside modulus method of Calculator Library ") ; 
   return firstNumber%secondNumber; 
}  
int random(int no){ 
   return new Random().nextInt(no); 
}

Next, we will import the library −

import 'calculator.dart';  
void main() {
   var num1 = 10; 
   var num2 = 20; 
   var sum = add(num1,num2); 
   var mod = modulus(num1,num2); 
   var r = random(10);  
   
   print("$num1 + $num2 = $sum"); 
   print("$num1 % $num2= $mod"); 
   print("random no $r"); 
} 

The output of the program will be-

inside add method of Calculator Library  
inside modulus method of Calculator Library  
10 + 20 = 30 
10 % 20= 10 
random no 0