Dart

Intro to Dart

When you create a dart file and start writing a program, there is no need to use any access specifiers. Everything is public by default. Dart does not support any access specifiers.

The main function is really simple. In java:

public static void main(String[]args)

In Dart:

void main()

Or if you need command line arguments:

void main(List<String> args)

It is pretty clear from these examples that the syntax of Dart is way more simple and compact than in Java. In Dart, code can be defined inside, as well as outside the classes.

Another difference in Dart and Java is indentation. Dart uses 2-character indentation, instead of 4.

Constructors in Dart

In Dart, declaration of constructors takes just a line. For example a constructor for a Bicycle class is:

Bicycle(this.var1, this.var2, this.var3 );

Keep in mind:

Constructors without bodies are valid in Dart.
A semicolon(;) at the end of the constructor is really important.
Using this in the constructor is a shortcut. The constructor mentioned above is equivalent to:

Bicycle(int var1, int var2, int var3) {
this.var1 = var1;
this.var2 = var2;
this.var3 = var3;
}

In the main function, you can directly assign the values to a variable as well as call the constructor at the same time. Following are two examples which show how to print the data stored in a variable:

Example 1:

var bike = new Bicycle(3,10,7)
print(bike);

Output:

Instance of 'Bicycle'

Example 2:

Now we will use toString() function to give us the value stored in bike. In the class, override toString() to get the output.

@override
String toString() => 'Bicycle: $var2 kmph'

Then write the same main method as above.

Output:

10 kmph

If you do $var1 instead of $var2, you will get 3 kmph as output.

If you want to print more than one variable:

@override
String toString() => 'Bicycle: $var2 kmph $var1 $var3'

You can find the entire program which demonstrates these concepts here

Variables in Dart

In dart, variables can be declared simply using the keyword var. If you have to declare a variable which is not restricted to a single type, it can be declared as dynamic. For example:

var name = 'cnfb';
var name2 = "doho"; // in dart strings can be declared within single as well as double quotes.
dynamic name3 = 'efr';
String name4 = 'djjf';
int num = 5;

A simple program to explain the variables above can be found here.

Uninitialized variables have null value stored in them by default. This so as in dart, everything including numbers is an object.

Variables can also be declared as final or const(constant). If a variable is declared as final, it's value cannot be changed throughout the execution of the program. A variable declared as const, it is a compile time constant. const variables are implicitly final. Both of these types have to be initialized while they are being declared.

Difference between final and const:

The value of a non-final, non-const variable can be changed even if it has a constant value.

var y = const [];//value of y = [a,b,c...] can be updated later on
const z = [];//cannot be updated

A program to demonstrate this is here.

Data types in dart

There are the following data types in dart:

Numbers

There are two types of numbers in dart, int and double. The range of int is -2^63 to 2^63 - 1. double is used to store floating point decimal numbers of upto 64 bit precision. Some other are properties are storing numbers as hexadecimal format, or exponents etc.

var num = 0xABCD45;
var exp = 34e2;

Numbers and strings can be inter-converted whenever needed. For this parse and toString() methods are used. For converting string to integer:

var number = int.parse(`34`);

For converting string to double:

var floating = double.parse(`23.4`);

For converting numbers to string:

String one = 1.toString();
String decimal = 45.676.toString();
String fixedPoints = 2.3463476.toStringAsFixed(3);

View this program to see how numbers can be used in dart.

Basic operations such as +,-,*,/ all can be performed on numbers. Bitwise operators can also be used. For more features, the dart math library has several built in functions.

Strings

A string is a collection of UTF-16 code units which can be declared either inside single or double quotes.

To use a single quote inside a sttring in ''. you need to do \'.

var s1 = 'I\`m human'`;

You can put the value of an expression inside a string by using ${expression}. If the expression is an identifier, you can skip the {}.

var s1 = 'Dart';
print("$s1 rocks!!");//Dart rocks!!

A raw string can be created using r'. A raw string is one in which everything is printed as it was entered. Even escape characters are not recognized in it.

var s = r'In a raw string, not even \n gets special treatment.';//In a raw string, not even \n gets special treatment.

Here is program to check out these things.

Using const with strings:

// These work in a const string.
const aConstNum = 0;
const aConstBool = true;
const aConstString = 'a constant string';

// These do NOT work in a const string.
var aNum = 0;
var aBool = true;
var aString = 'a string';
const aConstList = [1, 2, 3];

const validConstString = '$aConstNum $aConstBool $aConstString';
// const invalidConstString = '$aNum $aBool $aString $aConstList';

Boolean

To represent boolean values, bool is used. A bool type can store only true or false.

var t = true;
print(t);//true
bool r = false;
print(r);//false

Lists

Lists are the equivalent of arrays in Dart. Lists can be simply declared by :

var list = [1, 2, 3];

Lists can contain multiple data types. But if a list contains multiple data types, only printing can be done, no operations can be done.

var f = ["a", 5, 6];
print(f[0]);
var tmp = f[1] + f[2];//error
print(f[2]);//will print 6

To find the length of a list, simply do list.length. Compile time constatnt lists can be declared by doing:

var list = const [1, 2, 3];

A list can also be declared insdie a list.

var sublist = [[1, 2, 3], [4, 5], [5, 6, 7, 8]];

A program to demonstrate the lists concepts is here.

Maps

A map is a collection of key-value pairs. The key and value can be any type of objects. The key can occur only once, but the value can be repeated multiple number of times.

var map = {
//key:  value
  1:      'first',
  2:      'second'  
};

var mapdiff = {
  'one':   'first',
  'two':   'second'
};

These values and keys in a map can also be created using a map constructor.

var map = Map();//using new is optional in Dart2
map[1] = ['one'];

Values from a map can be accessed by:

var map = {
  'laugh':  'hahaha'
};
var tmp = map['laugh'];

map.length gives the number of key value pairs in a map.

Run this program to see the properties of maps.

Runes

Runes are the UTF-32 code points of a string. To define runes using a 4 digit hexdecimal number , do \uXXXX, where XXXX is the 4 digi thexadecimal number. In order to represent runes using less than or more than a 4 dgit hexadecimal number, do \u{......}.

The String class has several properties you can use to extract rune information. The codeUnitAt and codeUnit properties return 16-bit code units. Use the runes property to get the runes of a string.

Check out this program to see runes in action. The output of the above program will be :

👏
[55357, 56399]
[128079]
♥  😅  😎  👻  🖖  👍

Symbols

Symbols are rarely used objects in Dart which represent an operator or identifier. they’re invaluable for APIs that refer to identifiers by name, because minification changes identifier names but not identifier symbols. Symbols are compile time constamts..

To get the symbol for an identifier, use a symbol literal, which is just # followed by the identifier:

#radix
#bar

Read only Variables, Getters and Setters in dart

You can make a variable read only in Dart by adding an underscore before a variable. Here is a basic program which will explain getters and demonstrates read only variables in Dart.

yashk2000 / Dart