dart 语言 https://www.dartlang.org

Dart 入门基础 基础类型

变量 Variables

 var name = 'Bob';
//  dynamic name = 'Bob';
//  Object name = 'Bob';

//    name = new Object();

常量 Final and const

final name = 'Bob'; // Without a type annotation
final String nickname = 'Bobby';



const bar = 1000000; // Unit of pressure (dynes/cm2)
const double atm = 1.01325 * bar; // Standard atmosphere



  var foo = const [1];
  final bar = const [1,2,3];
  const baz =  const [5]; // Equivalent to `const []`

Built-in types

• numbers
• strings
• booleans
• lists (also known as arrays)
• maps
• runes (for expressing Unicode characters in a string)
• symbols

Numbers

• int
• double

int x = 1;
int hex = 0xDEADBEEF;

double y = 1.1;
double exponents = 1.42e5;

数字与布尔值

部分属性

int figureA = -93;

// figureA是否为负数
print(figureA.isNegative);

// figureA是否是有限的
print(figureA.isFinite);

// figureA是否正无穷大或负无穷大
print(figureA.isInfinite);


double figureB = 64.742;


// 返回figureB的符号，-1.0:值小于0、+1.0:值大于0、-0.0/0.0/NaN:值是其本身
print(figureB.sign);


// 返回figureB运行时的类型
print(figureB.runtimeType);

// 返回figureB的哈希码
print(figureB.hashCode);


int figureC = 13;

// figureC是否为奇数
print(figureC.isOdd);

// figureC是否为偶数
print(figureC.isEven);


// 返回figureC所占存储位
print(figureC.bitLength);

常用方法

int figureA = -93;

// 返回figureA的绝对值
print(figureA.abs());

// 返回figureA的字符串
print(figureA.toString());

double figureB = 64.742;
// 返回figureB的整数值
print(figureB.toInt());

// 返回figureB的双精度值
print(figureB.toDouble());

// 返回大于figureB的双精度值
print(figureB.ceilToDouble());

// 返回小于figureB的双精度值
print(figureB.floorToDouble());

// 返回figureB四舍五入的双精度值
print(figureB.roundToDouble());

// 返回figureB保留几位小数的字符串
print(figureB.toStringAsFixed(2));

// 返回figureB保留几位小数后精确结果的字符串
print(figureB.toStringAsPrecision(3));

int figureC = 31;
// figureC对比其他整数，0:相同、1:大于、-1:小于
print(figureC.compareTo(20));

// 将figureC控制在指定区间的整数
print(figureC.clamp(20, 25));

// 返回figureC转换成指定基数(进制)的字符串
print(figureC.toRadixString(16));

int figureD = 12;
// 返回figureD与其他整数的最大公约数
print(figureD.gcd(18));

// 返回figureDg与其他整数的截取余数
print(figureD.remainder(18));

// 返回figureD几次幂值的字符串
print(figureD.toStringAsExponential(2));

字符串常量与变量

字符串常量

String是一成不变的，一旦定义就不能改变

String name = "XiaoMing say : \n";
String say = """
Keep on going ...
never give up ...
never say die ...
""";
print(name + say);

部分属性

String str = "Hello world!";
// 返回字符串的UTF-16代码单元列表
print(str.codeUnits);
// 返回根据代码单元生成的哈希码
print(str.hashCode);
// 字符串是否为空
print(str.isEmpty);
// 字符串是否不为空
print(str.isNotEmpty);
// 字符串的长度
print(str.length);
// 返回字符串Unicode代码的可迭代对象
print(str.runes);
// 返回对象运行时的类型
print(str.runtimeType);

常用方法

返回对象的字符串表示

String str = "Hello world!";
print(str.toString());

截取字符串

String str = 'Dart is fun';
String newStr = str.substring(0, 4);
print(newStr);

在字符串中插入字符串

String name = "XiaoMing";
print("My name is ${name}");

输出字符串的Unicode编码

String str = "Dart";
print(str.codeUnitAt(0));
print(str.codeUnits);

去掉字符串前后空格

String str = "\tDart is fun\n";
print(str.trimLeft());
print(str.trimRight());
print(str.trim());

字符串的大小写转换

String str = "ABCdef";
print(str.toLowerCase());
print(str.toUpperCase());

拆分字符串

String strA = "Hello world!";
print(strA.split(" "));

String strB = "abba";
print(strB.split(new RegExp(r"b*")));

是否包含其他字符串

String str = 'Dart strings';
print(str.contains('D'));
print(str.contains(new RegExp(r'[A-Z]')));
print(str.contains('D', 0));
print(str.contains(new RegExp(r'[A-Z]'), 0));

在字符串前后补占位符

String str = "86";
print(str.padLeft(4, '0'));
print(str.padRight(4, '0'));

获取指定字符出现的位置

String str = 'Dartisans';

print(str.indexOf('art'));
print(str.indexOf(new RegExp(r'[A-Z][a-z]')));

print(str.lastIndexOf('a'));
print(str.lastIndexOf(new RegExp(r'a(r|n)')));

替换字符串中所有匹配字符

String str = "resume";
print(str.replaceAll(new RegExp(r'e'), 'é'));

字符串变量

StringBuffer是可改变的，定义后还可以再修改

StringBuffer xiaomingSaid = new StringBuffer();
xiaomingSaid.write("All the world's a stage ... ");
xiaomingSaid.write("And all the men and women merely players ...");
print(xiaomingSaid);

部分属性

StringBuffer strBuf = new StringBuffer();
strBuf.write("Sow nothing, reap nothing.");
// 返回字符串缓冲区的哈希码
print(strBuf.hashCode);
// 字符串缓冲区是否为空
print(strBuf.isEmpty);
// 字符串缓冲区是否不为空
print(strBuf.isNotEmpty);
// 返回字符串缓冲区累积内容的长度
print(strBuf.length);
// 返回对象运行时的类型
print(runtimeType);

常用方法

StringBuffer strBuf = new StringBuffer();
// 添加字符串到字符串缓冲区内
strBuf.write("Do one thing at a time, and do well.");
// 返回字符串缓冲区的所有内容
print(strBuf.toString());
// 清除字符串缓冲区
strBuf.clear();