Google Dart programming syntax and basic type Learning tutorial

1. Variable Declaration

How to define variables

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Var name = 'bob ';

Initial Value of a Variable

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Int lineCount;
Assert (lineCount = null); // Variables (even numbers) are initially null.

You can use var or directly specify the type.
Final: a variable defined as final. The value cannot be changed.

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Final name = 'bob'; // Or: final String name = 'bob ';
Name = 'Alice '; // ERROR

2. Basic Types

String

Single or double quotation marks can be used for strings.
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Var s1 = 'single quotes work well for string literals .';
Var s2 = "Double quotes work just as well .";


You can directly apply the value $ {expression} in the string. If it is only a variable, you can remove {}
Copy codeThe Code is as follows:
Var s = 'string interpolation ';
Assert ('dart has $ s, which is very handy. '=
'Dart has string interpolation, which is very handy .');
Assert ('That deserves all caps. $ {s. toUpperCase ()} is very handy! '=
'That deserves all caps. string interpolation is very handy! ');


Multi-line strings are considered to be concatenated by default.
Copy codeThe Code is as follows:
Var s = 'string' 'concatenation'
"Works even over line breaks .";
Assert (s = 'string concatenation works even over line breaks .');

If you want to use a multi-line string, you can use '''
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Var s1 = '''
You can create
Multi-line strings like this one.
''';


Create a character string without escaping
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Var s = @ "In a raw string, even \ n isn' t special .";

StringBuffer, very similar to. net.
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Var sb = new StringBuffer ();

Sb. add ("Use a StringBuffer ");
Sb. addAll (["for", "efficient", "string", "creation"]);
Sb. add ("if you are"). add ("building lots of strings .");

Var fullString = sb. toString ();

Number

There are two types: int and double. Both of them inherit the num type.

Conversion between numbers and strings

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// String-> int
Var one = Math. parseInt ("1 ");
Assert (one = 1 );

// String-> double
Varonepointone = Math. parseDouble ("1.1 ");
Assert (onePointOne = 1.1 );

// Int-> String
Var oneAsString = 1. toString ();
Assert (oneAsString = "1 ");

// Double-> String
Var piAsString = 3.14159.toStringAsFixed (2 );
Assert (piAsString = "3.14 ");


Boolean Type

Bool, unlike js, is false if it is not true.

Lists (can be used as an array)

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Var list = [1, 2, 3]; // instantiate a list
List. add (4); // add an element 4

You can use for, for... in, foreach () to traverse a list.
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Var list = [1, 2, 3];
For (final x in list ){
Print (x );
}


Or

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Var list = [1, 2, 3];
List. forEach (element) => print (element ));

Maps (Dictionary type)

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Var gifts = {// A map literal
// Keys Values
"First": "partridge ",
"Second": "turtledoves ",
"Th": "golden rings "};

Gifts ["third"] = "apple"; // Add

Use foreach to traverse
Copy codeThe Code is as follows:
Var gifts = {
"First": "partridge ",
"Second": "turtledoves ",
"Th": "golden rings "};
Gifts. forEach (k, v) => print ('$ k: $ V '));

GetKeys () and getValues () Methods
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Var gifts = {"first": "partridge", "second": "turtledoves "};
Var values = gifts. getValues ();

// Print partridge and turtledoves, but not necessarily in that order.
Values. forEach (v) => print (v ));