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Tutorial 6

Dart Language

Dart - Overview

The Dart programming language is a general purpose programming language developed by Google. It is widely used at Google and the programming language Flutter development.

The syntax of Dart is very close to Java and C++. Therefore, the object oriented language is very approachable for developers with knowledge in other programming languages.

Dart is an object-oriented language with C-style syntax which can optionally trans compile into JavaScript. It supports a varied range of programming aids like interfaces, classes, collections, generics, and optional typing.

Dart - Syntax

Syntax defines a set of rules for writing programs. Every language specification defines its own syntax. A Dart program is composed of −

Variables and Operators
Classes
Functions
Expressions and Programming Constructs
Decision Making and Looping Constructs
Comments
Libraries and Packages
Typedefs
Data structures represented as Collections / Generics

First Dart Code:

main() {
    print("Hello World!");
}

The main() function is a predefined method in Dart. This method acts as the entry point to the application.

print() is a predefined function that prints the specified string or value to the standard output i.e. the terminal.

Semicolon in Dart

The semicolon is used to terminate the statement that means, it indicates the statement is ended here. It is mandatory that each statement should be terminated with a semicolon(;).

Whitespace and Line Breaks

The Dart compiler ignores whitespaces. It is used to specify space, tabs, and newline characters in our program. It separates one part of any statement from another part of the statement.

Block in Dart

The block is the collection of the statement enclosed in the curly braces. In Dart, we use curly braces to group all of the statements in the block. Consider the following syntax.

{ //start of the block
    //block of statement(s)
}// end of the block

Dart - Identifiers

Identifiers are names given to elements in a program like variables, functions etc. The rules for identifiers are −

Identifiers can include both, characters and digits. However, the identifier cannot begin with a digit. Invalid - 1number
Identifiers cannot include special symbols except for underscore (_) or a dollar sign ($). Example : Valid - $result, first_name, Invalid - first-name
Identifiers cannot be keywords.
They must be unique.
Identifiers are case-sensitive. Example : firstName and FirstName are different.
Identifiers cannot contain spaces. Example : first name

Dart - Comments

Comments are the set of statements that are ignored by the Dart compiler during the program execution.
Comments are a way to improve the readability of a program.
Comments can be used to include additional information about a program like author of the code, hints about a function/ construct etc.

Types of Comments

Dart supports the following types of comments −

Single-line Comments
Multi-line Comments
Documentation Comments

Example :

//Single-line comments
    
/* Multi-line comments */

Dart Documentation Comment

The document comments are used to generate documentation or reference for a project/software package. It can be a single-line or multi-line comment that starts with /// or /*.

We can use /// on consecutive lines, which is the same as the multiline comment

///This  
///is   
///a example of  
///multiline comment

Dart - Keywords

Dart Keywords are the reserve words that have special meaning for the compiler. It cannot be used as the variable name, class name, or function name. Keywords are case sensitive; they must be written as they are defined.

The following table lists some keywords in Dart.

else	super	enum	in
switch	assert	extends	is
this	throw	break	true
case	factory	new	try
catch	false	null	class
final	on1	var	const
finally	void	continue	for
while	rethrow	with	default
return	do	if

contextual keywords.

They have special meaning and used in particular places.

async

sync

hide

show

asynchrony

These are newly added keyword

await

yield

built-in identifiers.

These types of keywords are used to porting of JavaScript code for Dart, these keywords are treated as a valid identifier, but they cannot be used in the class name function name, or import prefixes.

abstract	as	import	export
interface	extension	library	external
mixin	typedef	operator	part
covarient	Function	get	deffered
set	dynamic	implements	static

Dart - Data Types

The data types are the most important fundamental features of programing language.

In Dart, the data type of the variable is defined by its value.

The variables are used to store values and reserve the memory location.

The data-type specifies what type of value will be stored by the variable. Each variable has its data-type.

The Dart is a static type of language, which means that the variables cannot modify.

The Dart language supports the following types−

Number
Strings
Boolean
Lists
Maps
Runes
Symbols

Number

The Darts Number is used to store the numeric values. The number can be two types - integer and double.

Integer − Integer values represent non-fractional values, i.e., numeric values without a decimal point. For example, the value "10" is an integer. Integer literals are represented using the int keyword.
Double − Dart also supports fractional numeric values i.e. values with decimal points. The Double data type in Dart represents a 64-bit (double-precision) floating-point number. For example, the value "10.10". The keyword double is used to represent floating point literals.

int marks = 80;
double pi = 3.14;

Strings

Strings represent a sequence of characters. We store the data like - name, address, special character, etc. It is signified by using either single quotes or double quotes. A Dart string is a sequence of UTF-16 code units.

var lang = "Dart";

Boolean

The Boolean type represents the two values - true and false. The bool keyword uses to denote Boolean Type. The numeric values 1 and 0 cannot be used to represent the true or false value.

bool isValid = true;

Lists

A List is an ordered group of objects. The List data type in Dart is synonymous to the concept of an array in other programming languages.

var list = [1,2,3];

Maps

The maps type is used to store values in key-value pairs. Each key is associated with its value. The key and value can be any type.

In Map, the key must be unique, but a value can occur multiple times.

var student = {'name': 'AJ',  'age':32, 'Language': 'Dart'}

Runes

Strings are a sequence of characters. Dart represents strings as a sequence of Unicode UTF-16 code units. Unicode is a format that defines a unique numeric value for each letter, digit, and symbol.

A rune is an integer representing a Unicode code point.

The String class in the dart:core library provides mechanisms to access runes

Symbols

Symbols in Dart are opaque, dynamic string name used in reflecting out metadata from a library.

It usually refers to identifiers by name, because identifier names can vary but not identifier symbols.

Dart symbols are dynamic string name that is used to derive the metadata from a library. It mainly accumulates the connection between human-readable strings that are enhanced to be used by computers.

Dart - Variable

Variable is used to store the value and refer the memory location in computer memory. Variable names are called identifiers. We have already learnt about identifiers.

var lang = "Dart";

How to Declare Variable?

We need to declare a variable before using it in a program. In Dart, The var keyword is used to declare a variable.

The Dart compiler automatically knows the type of data based on the assigned to the variable because Dart is an infer type language.

Syntax -

var <variable_name>  = <value>;

Type Annotations

Dart supports type-checking by prefixing the variable name with the data type. Type-checking ensures that a variable holds only data specific to a data type.

Syntax -

<type> <variable_name>;

Example -

int age;

The dynamic keyword

Variables declared without a static type are implicitly declared as dynamic. Variables can be also declared using the dynamic keyword in place of the var keyword.

Example -

dynamic name = "AJ";

Final and Const

The final and const keyword are used to declare constants.

Dart prevents modifying the values of a variable declared using the final or const keyword. These keywords can be used in conjunction with the variable’s data type or instead of the var keyword.

Example -

final name = "AJ";
const pi = 3.14;

Dart - Operators

An operator is a symbol that is used to manipulating the values or performs operations on its operand.

Dart provides an extensive set of built-in operators to accomplish various types of operations.

There are several types of operators.

Arithmetic Operators
Assignment Operators
Relational Operators
Type test Operators
Logical Operators
Bitwise Operator
Conditional Operators
Casecade notation(..) Operators

Arithmetic Operators

Arithmetic Operators are the most common operators that are used to perform addition, subtraction, multiplication, divide, etc.

Operator Name	Description
Addition(+)	It adds the left operand to the right operand.
Subtraction(-)	It subtracts the right operand from the left operand.
Divide(/)	It divides the first operand by the second operand and returns quotient.
Multiplication(*)	It multiplies the one operand to another operand.
Modulus(%)	It returns a reminder after dividing one operand to another.
Division(~/)	It divides the first operand by the second operand and returns integer quotient.
Unary Minus(-expr)	It is used with a single operand changes the sign of it.

Assignment Operator

Assignment operators are used to assigning value to the variables.

Operator Name	Description
= (Assignment Operator)	It assigns the right expression to the left operand.
+= (Add and Assign)	It adds right operand value to the left operand and resultant assign back to the left operand.
-= (Subtract and Assign)	It subtracts right operand value from left operand and resultant assign back to the left operand.
= (Multiply and Assign)*	It multiplies the operands and resultant assign back to the left operand.
/= (Divide and Assign)	It divides the left operand value by the right operand and resultant assign back to the left operand.
~/= (Divide and Assign)	It divides the left operand value by the right operand and integer remainder quotient back to the left operand.
%= (Mod and Assign)	It divides the left operand value by the right operand and remainder assign back to the left operand.
<<= (Left shift AND assign)	The expression a <<= 3 is equal to a = a << 3
>>= (Right shift AND assign)	The expression a >>= 3 is equal to a = a >> 3
&= (Bitwise AND assign)	The expression a &= 3 is equal to a = a & 3
^= (Bitwise exclusive OR and assign)	The expression a ^= 3 is equal to a = a^3
\|= (Bitwise inclusive OR and assign)	The expression a \|= 3 is equal to a = a\|3

Equality and Relational Operators

Relational operators or Comparison operators are used to making a comparison between two expressions and operands. The comparison of two expressions returns the Boolean true and false.

Operator Name	Description
>	Greater than
<	Lesser than
>=	Greater than or equal to
<=	Lesser than or equal to
==	Equality
!=	Not equal

Type test Operators

The Type Test Operators are used to testing the types of expressions at runtime.

Operator Name	Description
as	It is used for typecast.
is	True if the object has the specified type
is!	False if the object has the specified type

Logical Operators

The Logical Operators are used to evaluate the expressions and make the decision.

Operator Name	Description
&& (AND)	The operator returns true only if all the expressions specified return true
\|\| (OR)	The operator returns true if at least one of the expressions specified return true
! (NOT)	The operator returns the inverse of the expression’s result.

Bitwise Operators

The Bitwise operators perform operation bit by bit on the value of the two operands.

Operator Name	Description
& (Binary AND)	It returns 1 if both bits are 1.
\| (Binary OR)	It returns 1 if any of bit is 1.
^ (Binary XOR)	It returns 1 if both bits are different.
~ (Ones Compliment)	It returns the reverse of the bit. If bit is 0 then the compliment will be 1.
<< (Shift left)	The value of left operand moves left by the number of bits present in the right operand.
>> (Shift right)	The value of right operand moves left by the number of bits present in the left operand.

Conditional Operators (?:)

The Conditional Operator is same as if-else statement and provides similar functionality as conditional statement. It is the second form of if-else statement. It is also identified as "Ternary Operator".

Syntax 1:

condition ? exp1 : exp2

If the given condition is TRUE then it returns exp1 otherwise exp2.

Syntax 2:

exp1 ?? expr2

If the exp1 is not-null, returns its value, otherwise returns the exp2's value.

Cascade notation Operators

The Cascade notation Operators (..) is used to evaluate a series of operation on the same object. It is an identical as the method chaining that avoids several of steps, and we don't need store results in temporary variables.

Dart - Constants

Dart Constant is defined as an immutable object, which means it can't be changed or modified during the execution of the program. Once we initialize the value to the constant variable, it cannot be reassigned later.

Defining/Initializing Constant

The Dart constant can be defined in the following two ways.

Using the final keyword
Using the const keyword

The keywords final and const are used to create a constant variable. Dart will throw an exception if we try to modify the constant variable.

Syntax:

final const_name;  
or
final data_type const_name

const const_name  
Or  
const data_type const_name

Dart - Number

The Number is the data type that is used to hold the numeric value. In Dart, It can be two types -

Integer
Double

Integer

Integer numbers are the whole numbers means that can be written without a fractional component.
An integer number can be signed or unsigned.
The representation of the integer value is in between -263 to 263 non-decimal numbers.
The int keyword is used to declare integer value

Syntax:

int var_name

Double

The Double number are the numbers that can be written with floating-point numbers or number with larger decimal points.
The double keyword is used to declare Double value

Syntax:

double var_name

Example :

void main() { 
    // declare an integer
    int num1 = 10;             
     
    // declare a double value
    double num2 = 10.50;  

    // print the values
    print(num1);
    print(num2);
}

Number Properties

Properties	Description
isFinite	If the given number is finite, then it returns true.
isInfinite	If the number infinite it returns true.
isNan	If the number is non-negative then it returns true.
isNegative	If the number is negative then it returns true.
sign	It returns -1, 0, or 1 depending upon the sign of the given number.
isEven	If the given number is an even then it returns true.
isOdd	If the given number is odd then it returns true.

Number Methods

Method	Description
abs()	It gives the absolute value of the given number.
ceil()	It gives the ceiling value of the given number.
floor()	It gives the floor value of the given number.
compareTo()	It compares the value with other number.
remainder()	It gives the truncated remainder after dividing the two numbers.
round()	It returns the round of the number.
toDouble()	It gives the double equivalent representation of the number.
toInt()	Returns the integer equivalent representation of the number.
toString()	Returns the String equivalent representation of the number.
truncate()	Returns the integer after discarding fraction digits.

Parsing

The parse() static function allows parsing a string containing numeric literal into a number.

The parse function throws a FormatException if it is passed any value other than numerals.

Example :

void main() { 
    print(num.parse('12')); //print 12
    print(num.parse('12.10')); //print 12.10
    
    //this will give exception
    print(num.parse('AAAA'));
}

To be continue for more...

Tutorial 6 - Dart Language