I am trying to print the 3 variables 2 from the superclass and one from the subclass but the variable of the subclass always printed out null when I use the mentioned method

import java.util.Scanner;    
public class Main {  
  public static void main(String[] args) {
      
        Scanner info=new Scanner(System.in);
        
        
        System.out.println("Enter the father name ");
        String firstname=info.next();
        
        System.out.println("Enter the grandfather name ");
        String lastname=info.next();
        
        System.out.println("Enter the child name ");
        String name=info.next();
        
        child one = new child(firstname,lastname,name);
        
        
       
       one.print_names();
        
        
        


    
  }  
}  

the classes

class dad{
  String firstname;
  String lastname;
    
dad (String firstname,String lastname){
    this.firstname=firstname;
    this.lastname=lastname;
}
    
}

class child extends dad{
  String name;
    
child(String firstname,String lastname,String name){
    super(firstname,lastname);
    name=name;
}

String childprint(){
    System.out.println(name);
    return name;
    
}
String print_names(){
    
    System.out.println( "your name is= "  name  " " firstname " " lastname);
    return name;
}
}

The output

Enter the father name

k

Enter the grandfather name

g

Enter the child name

f

your name is= null k g

CodePudding user response：

In your child constructor you wrote name = name.

You need to write this.name instead of just name.

When you write name, it refers to the parameter. When you write this.name, it refers to the object member named name.

CodePudding user response：

There are two things I'd like to address here:

1. In java we capitalize class names like so: Data or Child
2. When using a constructor, use this. to assign the value to the class instance rather than the constructor arg

CodePudding user response：

I think you only need to initialize your "name" parameter in the child constructor. I mean: where you declare "name=name" you should state "this.name = name" . That will tell the constructor that the value of the value of the variable name is the one provided inside the parenthesis. I hope it helps!