Google Dart programming syntax and basic types learning tutorial_Basic knowledge

1. Variable declaration

How to define variables

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var name = 'Bob';

Initial value of variable

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int lineCount;
assert(lineCount == null ); // Variables (even numbers) are initially null.

You can use var or specify the type directly.
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 type

String

Strings can use single quotes or double quotes.

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var s1 = 'Single quotes work well for string literals. ';
var s2 = "Double quotes work just as well.";

In a string, you can apply the value directly, ${expression}, if it's just a variable , you can remove {}

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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 string, will Considered the default splice.

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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 do this, use '''

to copy the code The code is as follows:

var s1 = '''
You can create
multi-line strings like this one.
''';

Create one Do not consider escaped strings

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var s = @" In a raw string, even n isn't special.";

StringBuffer, very similar to that in .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();

Numbers

There are mainly two types, int and double, they both 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
var onePointOne = 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, different from js, as long as it is not true, it is false.

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 = {                                                                                              // Keys Values
"first" : "partridge",
"second" : "turtledoves",
"fifth" : "golden rings"};
gifts["third"] = "apple"; //Add a

Use foreach to traverse

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var gifts = {
"first" : "partridge",
"second": "turtledoves",
"fifth" : "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));