Thread: related to static! need help

Hello,
Below is my code for Stack implementation.

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package doubt1;
 
/**
 *
 * @author Rohan <Rohan at Home Workstation>
 */
import java.io.*;
 
class Stack3 {
 
    int stack[];
    int tos;
 
    void push(int ele1) {
        stack[++tos] = ele1;
    }
 
    int pop() {
 
        int ele2 = stack[tos];
        tos--;
        return ele2;
    }
 
    void contents() {
        if (tos == -1) {
            System.out.println("Stack empty");
        } else {
            System.out.println("Contents of stack are");
            for (int i = tos; i >= 0; i--) {
 
                System.out.println(stack[i]);
            }
        }
    }
 
    Stack3() {
        stack = new int[10];
        tos = -1;
    }
}
 
public class Doubt1 {
 
    public static void main(String args[]) throws java.io.IOException {
        Stack3 stackcopy = new Stack3();
 
 
 
        String choice = null;
        int getchoice;
        char menucontinue = 't';
        do {
            System.out.println("---Stack Menu---");
            System.out.println("");
            System.out.println("1:Push");
            System.out.println("2:Pop");
            System.out.println("3:Contents of Stack");
            System.out.println("4:Exit");
            System.out.println("");
            BufferedReader is = new BufferedReader(
                    new InputStreamReader(System.in));
            System.out.println("Enter your choice");
            choice = is.readLine();
            getchoice = Integer.parseInt(choice);
 
            switch (getchoice) {
                case 1:
                    if (stackcopy.tos == 9) {
                        System.out.println("Stack full");
                    } else {
                        String pushele = null;
                        int ele;
                        BufferedReader is1 = new BufferedReader(
                                new InputStreamReader(System.in));
                        System.out.println("Enter element to be inserted");
                        pushele = is1.readLine();
                        ele = Integer.parseInt(pushele);
                        stackcopy.push(ele);                   }
                    break;
                case 2:
                    if (stackcopy.tos == -1) {
                        System.out.println("Stack Empty");
                    } else {
                        int popele;
                        popele = stackcopy.pop();
                        System.out.println("Element poped is " + popele);
                    }
                    break;
 
                case 3:
                    stackcopy.contents();
                    break;
 
                case 4:
                    menucontinue = 'f';
                    break;
 
                default:
                    System.out.println("Enter valid choice");
                    break;
            }
 
 
        } while (menucontinue == 't');
 
    }
}

Its working fine without errors and exception.

I have created an instance of class Stack3.But how is my static main() method able to access non static variables,and pass it topush(int ele1) method of Stack3 class. By definition and Java Language specification "a static method cannot access
non-static data

But again if i try to pass non static variable to a class method in main() in another program

package doubt2;
import java.io.*;
/**
 *
 * @author Rohan <Rohan at Home Workstation>
 */
class D{
void call(){}
void fill(int g){}
}
public class Doubt2 {
int k=9;
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) throws java.io.IOException {
        // TODO code application logic here
        D d = new D();        
        d.call();
        d.fill(k);
 
    }
}

Its giving the required error...
i.e non static variable cannot be referenced from a static context.

What is the problem or where am i going wrong in understanding the concepts of static? Kindly help me.Getting too confused

Its giving the required error...

Please post the full text of the error message. It contains useful information in fixing the problem.
Like the line number and the text of the source.

The problem is passing an nonstatic variable to a non static method
from static method main().

Static blocks or methods are executed before everything else in your program and non static variables take memory when they are called, so does the static. Well, let's have an example;
Let's say we have a method X which is static and one more method Y that is non static.
There are four variables, a,b,c,d of some primitive data type.
According to the rules, X will take memory very first while a,b,c,d didn't even called yet so when you will try to access a,b,c,d (any of them) how do you think that it will let you access them. As they have no space in the memory yet.


Moreover, as said by Norm, post your error message so that we could have a look into that and could help you more appropriately.

Originally Posted by rohan22

I think i am very close to solving it.Just tell me one thing.Now(below i have written a short code about
the scenario) suppose if i have a static method X(). And in that if i declare a variable called int i.Now
is int i implicitly static even though i have not declared it as static int i.If "Yes" then it solves
my problem.
Here is a code snippet.

static void X(){
int i;                // is int i implicitly static if declared in a static method?
}

Or in the above code if int i is not static implicitly......... is it that static methods can actually have nonstatic
variables along with static variables?

NO!!!!
And did you try it?

Originally Posted by rohan22

Yes I have tried and its working Fine.Try the below code:

class D {
int k;
 
 void fill(int g) {
        k = g;
        System.out.println("k is " + k);
    }
}
 
public class Temp {
 
    public static void main(String[] args) {
        int m = 9;
        D d = new D();
 
 
        System.out.println("m is " +m);
        d.fill(m);
    }
}

Do you think m is static? NO!!!
m is being passed as argument to fill() of Class D and class D doesn't even know m. Your concept about static is wrong. This method you have tried is called value passing to the methods. Nothing else. m is not static.

suppose if i have a static method X(). And in that if i declare a variable called int i.Now
is int i implicitly static even though i have not declared it as static int i

This was your question, so i replied NO and i can never be implicitly static.

Originally Posted by Mr.777

Do you think m is static? NO!!!
m is being passed as argument to fill() of Class D and class D doesn't even know m. Your concept about static is wrong. This method you have tried is called value passing to the methods. Nothing else. m is not static.

This was your question, so i replied NO and i can never be implicitly static.

Yes i got to know that m is int and not static int in netbeans debugger when i review the contents of m.

Or in the above code if int i is not static implicitly......... is it that static methods can actually have nonstatic
variables along with static variables?

But my question was can static methods have non static variables also.And yes i can conclude that it can have.
Am i right?

Yes. They can have non static variables.

Originally Posted by Mr.777

Yes. They can have non static variables.

Cool............ thanks.....

Is there confusion here between local variables which all methods can have (m is local)
and static class variables?
Method can not define local static variables.