access non static data in static method in java

Question

i am a new java learner and i am making a program where i want to access the value of a not static data member in a static method but rule says that i cant not do this but we can access it after creating a object my question is that if i make a object of that class that old value of that data member is erase why ? how can i use it old value of a not static data member in a static method

import java.util.Scanner;
class emp
{
     String name;
     int rate;
     static String c_name="TCS";


     void setdata(String n,int s)

     {
       name=n;
       rate=s;  

     }
     static void employee_salary_cal(int t)
      {
        int day,rate1,Total;
        day=t;
        emp e2=new emp();
        rate1=e2.rate;
        Total=rate1*day;

        System.out.println("Total salary " +Total);
      }  

     void showData()
     {
       System.out.println("Employee name = " +name);
       System.out.println("Employee pay rate per day = " +rate);
     }


}

class emp_main
{
  public static void main(String args[])
     { 
        int da;
        emp e1=new emp();
        e1.setdata("alex",100);
        System.out.println("Company name = " +emp.c_name);
        e1.showData();
        System.out.println("Enter Work days in months ");
        Scanner sc=new Scanner(System.in);
        da=sc.nextInt();
        emp.employee_salary_cal(da);



     }
}

program output :

Company name = TCS
Employee name = alex
Employee pay rate per day = 100
Enter Work days in months
25
Total salary 0

Assuming you have to use a static method for this, pass an emp object to your employee_salary_cal method instead of just passing an int. — Luiggi Mendoza
– Luiggi Mendoza, Commented Sep 9, 2013 at 20:41
possible duplicate of how to access a non static member from a static method in java? — Simon
– Simon, Commented Sep 9, 2013 at 20:43
@Simon this is not the same, note that the answer with most upvotes propose the usage of a Singleton which is not the right solution in this case. — Luiggi Mendoza
– Luiggi Mendoza, Commented Sep 9, 2013 at 20:45
no answer to you question, but please use the java code conventions: oracle.com/technetwork/java/javase/documentation/… — Christian Kuetbach
– Christian Kuetbach, Commented Sep 9, 2013 at 20:46

Georgian · Accepted Answer · 2013-09-09 20:42:41Z

5

Just pass your emp object to the static method, instead of creating a new instance of it. The "rule" is that you can't access instance variables and methods, but a static method can receive external objects and fiddle with them.

static void employee_salary_cal(emp e, int t)
{
    System.out.println("Total salary " + e.rate * t);
}

On another note, you are lacking serious programming fundamentals. I recommend you follow some really basic tutorials, again.

answered Sep 9, 2013 at 20:42

Georgian

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3 Comments

Luiggi Mendoza Over a year ago

Or easier, have a non-static employee_salary_cal(int t) method that handles this.

Georgian Over a year ago

@LuiggiMendoze Well duh, but I'm willing to bet that this is a homework assignment, and he's required to make use of the static keyword.

Luiggi Mendoza Over a year ago

Yes this appears to be the case, still the advice you explain in your answer doesn't explains that, duh

Logan Murphy · Accepted Answer · 2013-09-09 20:46:37Z

2

why would you use static at all for the function? Use the this context.

 void employee_salary_cal(int day)
  {
    System.out.println("Total salary " + (this.rate * day));
  }

Then you can just call it as an instance function like so

emp e = new emp();
e.employee_salary_cal(5);

answered Sep 9, 2013 at 20:46

Logan Murphy

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Comments

user2209008 · Accepted Answer · 2013-09-09 20:42:55Z

0

Pass the object you want to work with into the static function as an argument.

static void employee_salary_cal(emp employee, int t)

answered Sep 9, 2013 at 20:42

user2209008

Comments

Cruncher · Accepted Answer · 2013-09-09 20:46:58Z

0

It wouldn't make sense to be able to access an instance variable from a static context.

For each class there is exactly 1 set of static fields. However, each class could have any number of copies of each of its instance variables. The JVM would have no idea which copy of the instance variable you were talking about.

Like other have stated, if you want to access an instance from static, you have to tell the static method which instance, by passing the instance into it.

answered Sep 9, 2013 at 20:46

Cruncher

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Comments

Christian Kuetbach · Accepted Answer · 2013-09-09 20:54:56Z

0

The difference between static and non-static:

class MyClass {
    public int nonStatic=1;
    public static int isStatic = 2;
}

MyClass a=new MyClass();  
a.nonStatic = 3          // nonStatic =3; isStatic=2
MyClass b=new MyClass(); // nonStatic =1; isStatic=2
MyClass.isStatic = 3;    // nonStatic =1; isStatic=3
MyClass c=new MyClass(); // nonStatic =1; isStatic=3

What I want to explain is, If you create N instances of MyClass, you also create N values (or more precise int-pointer in memory) for nonStatic, but only one for isStatic;

answered Sep 9, 2013 at 20:54

Christian Kuetbach

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