Support Data Types

There are five types in dart:

• numbers
• Strings
• Booleans
• Lists
• Maps

Before we talk about data types,we would see how to define the variable in dart.To define a variable ,there are many ways to do it.The keywords are var and dynamic

String nickName ="Nie Bin" ;//define a variable named nickName and the type is String
var age = 18 ; // define a variable named age and the type is dynamic with int ,if you assign the age ="nie bin" ;,there will be an error.
dynamic address = "ShangHai";  // the variable name is address and have a dynamic type that you can assign any to it, if you assign address =1 ; there will not be an error.

The code above is about how define a variable that can assign a value again, you want to define a constant that do not change in the compile time, you should use the keywords of const and final

const NIE_BIN = "Nie Bin"; //as you see   the value is 'Nie Bin',but you can not assign again.
final AGE = 18; // you can only set once,if you assign again it will say error.

If you define a variable that is not final or const, but not assign its value ,it will assign a value of null, whatever its type is.

Numbers

There are only two types numbers in dart,which are int and double. The int represents the integers and the double represents fractional numbers. So it is very ease to use and remember.example below :

var a = 1 ; //auto convert to int.
var f = 1.1 ; //dynamic type to double.
print(a);
print(f);

As you know, the dart is an object-oriented language,so the variables of a,f are common object. These have some properties and functions. such as isEven , sign and so on. int is a class that extends num class.if you want to know more about its properties or functions , you can look at the source in an IDE.The other data types if you want to know are same as this way.

Strings

String is very common in developing,there are two ways to represent a single line of a String. The one is single quotes and the another one is double quotes. If you want to use the multi line of a String use the triple quotes.

var single_quote = 'this is single quote that is used to represent a single line string.' ;
var double_quote = "this is double quote that describe a single line string as well." ;
var triple_quote = """
  this is a triple quotes that are used to describe a multi lines strings. it is very similar to the python.
""" ;

We have a basic way of using string, let’s go far more deep with its operator of concatenation and interpolation. concatenation is just plus a string to another one with sign of +. interpolation makes the string as a variable in the quotes ,just use the characters $ or ${}. Examples are in the following:

  var single_quote = 'single quote';
  var double_quote = "double quote";
  var triple_quote = """triple quote""";

  var concatenation = 'this ' + single_quote;
  var inter1 = 'that ' + 'is interpolation example1:$double_quote';
  var inter2 = 'that ' + 'is interpolation example2:${triple_quote}';
  print(concatenation);
  print(inter1);
  print(inter2);

String is a class that implements Comparable<String> and Pattern and have some properties,functions too.if you want to know more about them ,just look its source code.

Booleans

The keyword is bool.its values have just two options of true and false. If a type is not a boolean and you use as a boolean ,it will compare with true value,the all of them are false,because the others are not equal true. Basic Example:

 var isCat = false;
 bool isT = true;
 print(isCat);
 print(isT);

List

List is an array in dart and have is order that start with zero and end in n-1,the n is its length.the list is same as the language of the java.There are two types of list,the one have a fixed length that you can not changed except at the initial time and the another one is a growable list that can grow or decrease its length.Examples below:

var names =new List(10);//this is a fixed length list, you can not change its length at the runtime.
var ages = new List();//this is a growable list.
var addresses = ["Shanghai", "BeiJing"]; // this is a growable list.

There are also some properties and functions in the List class, you can find in your source files.

Maps

A Map is data type of key-value.There are type ways for using a map that are {} and keyword of Map.Examples are in the following:

 var peopleMap = {'name1': "niebin", 'age': 12};// The a map literal `{}` is used in there.      
 for (var m in peopleMap.keys) {
   print(peopleMap[m]); //will print niebin and 12
 }

We use the map literal {} above.But we have the other way that use the constructor of Map as below:

 var anyMap = Map();// the constructor of `Map`
 anyMap['a'] = 1;
 anyMap['name'] = "xiao bai";
 anyMap['isDog'] = true;
 for (var k in anyMap.keys) {
   print(anyMap[k]);
 }

It is very easy to define or initialize the Map. There are some properties and functions in the Map,you can find them in the dart with its code sources files.

The End.