can any one explain how this.age= age+20 is giving 20 as output

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Completed the task just by hit and trial after reading all the comments of respected members Is there any difference between instance and local variable ? if I am correct this keyword is used to access the instance variable that is the local variable

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Anonymous #11263139

Level 7 , Mexico

9 February 2023, 19:58

I finished the task but: System.out.println("The age in adjustAge() is " + age); I think there is an error in codegym's solution, because it says this way, but in the conditions it says that it has to show age+20 in adjustAge: Shouldn't the - this- also be added there? System.out.println("The age in adjustAge() is " + this.age);

Gellert Varga

Level 23 , Szekesfehervar, Hungary

24 May 2020, 19:20

"Is there any difference between instance and local variable" : Yes, they are totally different. The "this" keyword is used to access a variable of the passed object. (In other words: to access an instance-variable.) Local variable: this is just a simple variable what you use in that method. Please send me exactly that program, which shows the '20' output. Then i can explain it in more details.

Seferi

Level 22 , United Federation of Planets

2 June 2020, 17:51

Thanks mate. This cleared it for me.

Dinesh

Level 7 , Delhi, India

17 January 2021, 14:31

/*  Comments are numbered as per flow of the program*/
public class AdjustAge{
    public static void main(String[] args) {

 //1 Person  object created & assigned to ref var person

        Person person = new Person();

  /*2 Print  Age by calling instance var(age)
    by obj ref (person) in print()*/

        System.out.println("Age: " + person.age);

  /*3. calling instance method adjustAge() of Person class
       by obj ref (person) and passing instance variable
       (age)  obj ref person */

        person.adjustAge(person.age);
        System.out.println("Adjusted age: " + person.age);
    }

    public static class Person {
        public int age = 20;

    /*4  method arg 20 get passed */

        public void adjustAge(int age) {

    /*5 Why not like age = this.age+20*/

            this.age = age + 20;
            System.out.println("The age in adjustAge() is " + age);

        }
    }
}
</

Gellert Varga

Level 23 , Szekesfehervar, Hungary

18 January 2021, 19:39

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

/*1) Person obj created & assigned to ref var person
This code calls the default constructor by Java, and it creates the obj.
The Person class has an instance-field in line 26, and this instance-field
(the age variable of the newly created object) will set to starter value 20 immediately.*/
     Person person = new Person();

/*3) Print age by calling the instance variable "age" of the "person" obj. So, it will print: 20 */
     System.out.println("Age: " + person.age);

/*4) calling instance method adjustAge() of Person class
by obj ref (person) and passing instance variable
(age)  obj ref person. - So, it will pass a primitiv variable (age),
so it passes just an int value not the object itself!!
Jump to the line 28. */
     person.adjustAge(person.age);

/*9) It prints 40. The person.age was set to 40, in line 35*/
     System.out.println("Adjusted age: " + person.age);
  }

//2) This constructor will created the obj, and sets its age variable to 20
   public static class Person {
     public int age = 20;

/*5) this instance method receives the value 20.
Here, this value is called “age”. It is a local variable here!*/
     public void adjustAge(int age) {

/*6) Why not like age = this.age+20 */
/* this.age means the age variable of "this"object; and the age variable on the right side
means the local variable (=20). They are two different age variables!*/
       this.age = age + 20; // 7.)The age variable of "this"object is 40 now!!!

/*8) The age variable in the print command means the local variable. =20*/
       System.out.println("The age in adjustAge() is " + age);
     }
   }
}

/*Plus extra:
Below is the same AdjustAge() meth., but with other variable names.
Maybe it's easier to understand this*/

/*public void adjustAge(int x) {
     this.age = x + 20;
     System.out.println("The age in adjustAge() is " + x);
  } */