Summary of Dart basic functions, classes, objects, static members, operators, inheritance and abstract class knowledge points

Functions in Dart

Classes and objects in Dart

1. Object oriented programming( OOP)The three basic characteristics are encapsulation, inheritance and polymorphism //Encapsulation: encapsulation is the main feature of object and class concepts. Encapsulate, encapsulate objective things into abstract classes, and provide some of their own attributes and methods to others //Inheritance: it can use the functions of existing classes, //Polymorphism: it is allowed to assign the pointer of subclass type to the pointer of parent type. The same function call will have different execution effects 2. Dart All things are objects, all objects are inherited from Object class 3. Dart Is an object-oriented language using classes and single inheritance. All objects are instances of classes, and all classes are Object Subclasses 4. A class is usually composed of properties and methods //An example of defining a base class: class Person{ String name = 'Zhang San'; int age = 23; void getInfo(){ print("$ --- $"); } } void main() { var p = new Person(); print(p.name); // Zhang San p.getInfo(); // Zhang San 23 } //Define classes with construction methods: class Person{ String name = 'Zhang San'; int age = 23; // Constructor Person(String name,int age){ this.name = name; this.age = age; this.getInfo(); // Wool --- 25 } // Another constructor shorthand for assignment // Person(this.name,this.age); void getInfo(){ print("$ --- $"); } } void main() { var p = new Person('Mao Mao',25); print(p.name); // Mao Mao } //Define a named constructor: class Person{ String name = 'Zhang San'; int age = 23; // Constructor Person(String name,int age){ this.name = name; this.age = age; this.getInfo(); // Wool --- 25 } // Named constructor Person.now(){ print('I'm a named constructor'); } // Get user information void getInfo(){ print("$ --- $"); } } void main() { var p = new Person.now(); // I'm a named constructor print(p.name); // Zhang San }

Inheritance of class static member operator class in Dart

Dart Static members in 1. Use static Key to implement class level variables and functions 2. Static methods can only access static members, non static methods can access static members //Code example: class Person{ int age = 20; String nameP = 'Zhang San'; // Static attribute static String name = 'Zhang San'; // Static method static void printInfo(){ print('This\'s a static function named printInfo.' ); } // Get user information static void getInfo(){ // this is not accessible in static static methods // print("$name --- $age"); // error Getter not found: 'age'. print(name); // Zhang San printInfo(); // This's a static function named printInfo. } } void main() { Person.getInfo(); }

Object operators in Dart

? Conditional operator // Person p; P as Type converter // If (P is person) p is Object is Type judgement // Judgement type .. Cascade operation (concatenation, similar to chain call operation) p1..name = "Zhang San 222" ..age = 30 ..printInfo();

Inheritance of classes in Dart:

class Person { int age = 20; String nameP = 'Zhang San'; Person(this.nameP, this.age); //... } class Child extends Person{ Child(String name, num age) : super(name, age){ } } void main() { Child c = new Child('Li Si', 23); c.getInfo(); }

class Child extends Person{ Child(String name, num age) : super(name, age); @override void printInfo(){ print("xxx xxx xxx xxx."); } }

super.funcName();

Abstract class, polymorphism and interface in Dart

// Define abstract class Animal abstract class Animal { eat(); // Abstract method } // Define Dog class to inherit abstract class Animal class Dog extends Animal{ @override eat(){ // TODO: implement eat print('dog eat something.'); return null; } run(){ print('run'); } } void main() { Animal dog = new Dog(); dog.eat(); // ok dog.run(); // error Dog d = new Dog(); d.eat(); // ok d.run(); // ok }

1. First, dart No interface for interface Keyword defines an interface, but ordinary or abstract classes can be implemented as interfaces. 2. Equally applicable implements Keyword implementation 3. however dart The interface of is a little strange. If the implemented class is a normal class, it will copy all the methods of the properties in the normal class and the abstract 4. Because abstract classes can define abstract methods, ordinary classes can't, so in general, if the implementation is like Java In the way of interface, abstract classes are usually used 5. It is recommended to use abstract classes to define interfaces code: abstract class Db { // As an interface: Convention and specification String uri; add(); save(); delete(); } class Mysql implements Db{ @overrive String uri; @overrive add() { //... } @overrive save() { //... } @overrive delete() { //... } } class Mongo implements Db{ @overrive String uri; @overrive add() { //... } @overrive save() { //... } @overrive delete() { //... } } //...

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6 February 2020, 01:57 | Views: 9575