Detailed explanation of dart class in java

dart is an object-oriented language; Object-oriented

Inheritance Encapsulation Polymorphism

Everything in dart is an object, and all objects are inherited from the object class

1 class is usually composed of properties and methods

In dart, if you want to customize a class, put this class outside the main function

Class name uses big hump method name uses small hump

1. Define the properties and methods of this class

// Definition 1 Properties and Methods of Classes 
class Person {
 String name = ' Zhang 3';
 int age = 19;
 void getInfo() {
  // print(' My name is $name, This year $age'); No. 1 1 Species 
  // It is recommended to write like this through this To visit 
  print("${this.name}====${this.age}");
 }
}

// Using properties and methods in a class 
void main() {
 //  Call Perso This class   You first need to instantiate this class 
 // Person p = new Person(); //  Equivalence  var p=new Person
 var p = new Person();
 print(p.age);
 p.getInfo();
}

2. Changing properties and methods in a class

class Person {
 String name = ' Zhang 3';
 int age = 19;
 void getInfo() {
  // It is recommended to use this writing 
  print("${this.name}====${this.age}");
 }
 // Restrict types and change properties and methods in classes 
 SetUserinfo(int age) {
  this.age = age;
 }
}

void main() {
 //  Call Perso This class   You first need to instantiate this class 
 Person p = new Person(); //  Equivalence  var p=new Person
 print(p.age);//19
 p.getInfo();// Zhang 3====19
 p.SetUserinfo(100);
 p.getInfo();// Zhang 3====100
}

3. Default constructor

class Person {
  // This is 1 Default constructors 
 Person() {
  print(' The contents of the default constructor, this method will automatically start when instantiating, ha ');
 }
}

void main() {
 //  When instantiated, the default constructor is automatically triggered 
 Person p = new Person(); //  Equivalence  var p=new Person
}

4. Dynamic passing, multiple instantiation of classes, printing different values

class Person {
 String name;
 int age;
 Person(String name, int age) {
  this.name = name;
  this.age = age;
 }
 void getuserInfo() {
  print(this.name);
  print(this.age);
 }
}

void main() {
 //  When instantiated, it will automatically trigger 
 Person p = new Person(' Zhang 3', 10); //  Equivalence  var p=new Person
 p.getuserInfo();

 // This class can be instantiated several times 
 Person v = new Person(' Zhang 31', 100); //  Equivalence  var p=new Person
 v.getuserInfo();
}

5. Abbreviation of default constructor

class Person {
 String name;
 int age;
 
 // Person(String name, int age) {
 //  this.name = name;
 //  this.age = age;
 // }
 // The code annotated above is equivalent to  Person(this.name, this.age);
 Person(this.name, this.age);
 void getuserInfo() {
  print(this.name);
  print(this.age);
 }
}

6. Named constructor, named constructor can be written multiple; But the default constructor can only write 1

class Person {
 // I am the default constructor 
 Person() {
  print(' I am the default constructor ');
 }
 //  Named constructor 
 Person.mynow() {
  print(' I am a named constructor ');
 }
}

void main() {
 //  When instantiated, the construction automatically triggers by default 
 Person p = new Person(); //  Equivalence  var p=new Person
 Person v = new Person.mynow(); //  Triggering a named constructor 
}

7. Pull out the class and put it in a separate folder

 Create in the root directory of the project 1 Folders  lib
 In lib Folder to create 1 Files  xxx.dart The contents are as follows 

class Person {
 // I am the default constructor 
 Person() {
  print(' I am the default constructor ');
 }
 //  Named constructor 
 Person.mynow() {
  print(' I am a named constructor ');
 }
}


 Introduce in a file that is required 
import 'lib/xxx.dart';
void main() {
 //  When instantiated, the construction automatically triggers by default 
 Person p = new Person(); //  Equivalence  var p=new Person
 Person v = new Person.mynow(); //  Triggering a named constructor 
}

8. dart modifier

dart is different from other object-oriented languages. There is no access modifier to public private

However, we can use _ to define a property or method as private (that is, add _ before the variable or method; And to separate him out into a file in the lib directory, so that the outside can not be accessed);

But I think this has no real meaning. If you want to access this private method, add a common method to the class; To access this private method; Access back at return; You can access this private method private method, only in the current class to access the animal. dart file in the lib directory;

The contents are as follows

class Animal {
 String _name = 'dog';// This is a private method, which can only be accessed by the current class; Other classes are inaccessible, ha ~ ; 
 //  If you have to access this class, you can access it through a common method 
 
 //  Access this class through public methods; Indirect access 
 getName(){
  print(this._name);
 }

 int age = 19;
 void getInfo() {
  // It is recommended to use this writing 
  print("${this._name}====${this.age}");
 }

 // Restrict types and change properties and methods in classes 
 SetUserinfo(int age) {
  this.age = age;
 }
}

9. Calculate the area of rectangle instead of get method

class Rect {
 num width;
 num height;
 Rect(this.width, this.height);
 getUserINfo() {
  return (this.width * this.height);
 }
}

void main() {
 //  When instantiated, the construction automatically triggers by default 
 Rect p = new Rect(10, 4); //  Equivalence  var p=new Person
 print(p.getUserINfo());
}

 Change the above code to read get Method 

class Rect {
 num width;
 num height;
 Rect(this.width, this.height);
 // getUserINfo() {
 //  return (this.width * this.height);
 // }

 //  Change the above code to get
 get getUserINfo {
  return (this.width * this.height);
 }
}

void main() {
 //  When instantiated, the construction automatically triggers by default 
 Rect p = new Rect(10, 4);
 // print(p.getUserINfo());
 //  Change the above code to read get Method call 
 print(p.getUserINfo);// When calling, the method is accessed directly by accessing the property 
}

10. set method in dart

class Rect {
 num width;
 num height;
 Rect(this.width, this.height);
 //  When setting the value. We used set Method 
 set areaHeight(value) {
  this.height = value;
 }
 get area {
  return this.height;
 }
}
void main() {
 //  When instantiated, the construction automatically triggers by default 
 Rect p = new Rect(10, 4);
 p.areaHeight = 6; // When 1 The interior of the class uses the set Method. We use assignment directly; 
 print(p.area); // Internally used get  We get the value directly through the attribute 
}

11. Before instantiating, initialize values inside the class

class Person {
 String name = ' Zhang 3';
 int age = 19;
 void getInfo() {
  // It is recommended to use this writing 
  print("${this.name}====${this.age}");
 }
 // Restrict types and change properties and methods in classes 
 SetUserinfo(int age) {
  this.age = age;
 }
}

void main() {
 //  Call Perso This class   You first need to instantiate this class 
 Person p = new Person(); //  Equivalence  var p=new Person
 print(p.age);//19
 p.getInfo();// Zhang 3====19
 p.SetUserinfo(100);
 p.getInfo();// Zhang 3====100
}

0