I am unable to print the null value programmatically of the following statement.

Under discussion

If a variable of a reference (composite) type isn't storing a reference to an object, then it stores what is known as a 'null reference'. IF String s; & String s=null; are same than why i am not getting null as output. Tried 2 Ex as follows but didn`t get null as output. 1.

class Person{
    public static void main(String[]args){

     String s;

    System.out.println(s);
    }

}

class Person{
    public static void main(String[]args){
        Person pr = new Person();

        System.out.println(pr);
    }

}

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Gellert Varga

Level 23 , Szekesfehervar, Hungary

6 January 2021, 14:29

public class CodeGym {
    static String str;
    public static void main(String[]args){
        System.out.println(str);
    }
}

Try it. Output: null

Guadalupe Gagnon

Level 37 , Tampa, United States

6 January 2021, 04:19

Class variables get set to a default when the object of that class is being constructed, and will remain the default value until changed. All objects get set to null as the default value, while primitives get set to 0. In the above code you are using local variables and they must be set before being used (even if it is to null). A class variable (also called field) is a variable declared in a class but outside any other blocks of code. A local variable is any variable declared in a block of code that is in a class.

Dinesh

Level 7 , Delhi, India

6 January 2021, 06:21

Thank You so much. Please check my implementation .Guide if any thing else required

class Codegym{
        Codegym person;
        static int i;
    public static void main(String[]args){

        Codegym cg = new Codegym();

        System.out.println(i);
        System.out.println(cg.person);
        System.out.println(cg);
    }

}

Guadalupe Gagnon

Level 37 , Tampa, United States

6 January 2021, 14:20

That should output: 0 null (address in memory for the object since no toString() method is defined Would be something like Codegym@6acbcfc0)

Dinesh

Level 7 , Delhi, India

7 January 2021, 05:43

Yes. Thanks I was going through the following Example from Level2 but not getting it. Here some object reference is being talked about I am not getting this. The Print command in bold (refer code) is giving output as you said earlier If possible please help me understanding this concept.

public class Codegym {
    public static void main(String[] args) {
        //write your code here
        Man man = new Man();
        Woman woman = new Woman();
        man.wife = woman;
        woman.husband = man;

        System.out.println(man.wife);
        System.out.println(woman.husband);

    }

    public static class Man {
        public int age;
        public int height;
        public Woman wife;
    }

    public static class Woman {
        public int age;
        public int height;
        public Man husband;
    }
}