Dart - this关键字

class Mobile {  
    String modelname;  
    int man_year;  
      
     // 创建构造函数 
    Mobile(modelname, man_year){  
             modelname = modelname;  
             man_year = 2020;  
             print("Mobile's model name is: ${modelname}, and the manufacture year is: ${man_year}");  
    }  
                                                              }  
    void main(){  
	Mobile mob = new Mobile("iPhone 11 ",2020);  
    }
}       

class Mobile {
    String modelname;
    int man_year;
    
    //Creating constructor
    Mobile(modelname, man_year){
       this.modelname = modelname;
       this.man_year = 2020;
       print("Mobile's model name is: ${modelname}, and the manufacture year is: ${man_year}");
    }
                                                              }
    void main(){
        Mobile mob = new Mobile("IPhone 11",2020);}
     }

this.modelname = modelname;
this.man_year = 2020;