global variable

[Andrew Lit]

Hi,
I thought if variable is global than it can be changed everywhere. But when i try this:

 
public class A(){
   public int y = 0;
   public void change(int ch){
     if(ch>0){
        ch *= (-1);
        y = ch;
     }
   }
   public void mmain(){
     y = 1
     cahnge(i);
     System.out.println(y);   //i get 1
   }
}

could you explain me why? and what should i do to get the result i want.
thank you

[bharat nagpal]

There are many mistakes in your code ,you have written here ....
this one serves your purpose.
yes you are right you can change global variable from anywhere in the class... because its has the class scope
____________________________

class CheckA {
public int y = 0;
CheckA() {
y = 1 ;
System.out.println("before:"+y);
change('i');
System.out.println("after:"+y);
}
public void change(int ch){
if(ch>0){
ch *= (-1);
y = ch;
}
}

public static void main(String args[]) {
new CheckA();
}
}

[Andrew Lit]

actually what i have is:

  
public class Launcher(){
  G main = new G();
  main.result();
}

  
public class G(){
int count = 0;
int size;       //defined elsewhere
  public G(){
  //....
  }
  public void insert(int start){
    //
  }
  public boolean test(int count){
   if(ccount>=size){
          ccount = size-1;
          count = ccount;
//count here is 4
       }
  } 
//let's say size was 5
  public void result(){
    boolean tf;
//...............
//count was 6
    tf = test(count);
//but count here is 6  :confused: 
// ..............
// why is it so?
  }
}

[Ron Newman]

Some of your methods have a parameter named "count". This parameter hides the instance variable of the same name.
While this is legal, it is poor style,and likely to cause exactly the kind of confusion you are encountering here.
[ October 26, 2002: Message edited by: Ron Newman ]

[bharat nagpal]

in the method test
test(int count)...
The variable count will be local to the method "test", and hide the
instance variable . if you want to change the value of instance variable here, either
dont name this local variable as "count", or use "this.count" for global variable.

[Dirk Schreckmann]

bhart1,
Welcome to JavaRanch!
We ain't got many rules 'round these parts, but we do got one. Please change your display name to comply with The JavaRanch Naming Policy.
Thanks Pardner! Hope to see you 'round the Ranch!

[bharat nagpal]

sorry ! It was my mistake , I'll take care in future. My another mistake is I've joined you people very late...

[Thomas Markl]

Check out this:
In this case x is a local variable which cannot be changed by „change(int ch)“ because
change() only changes a copy of the passed parameter. Change is only visible inside
chang(int ch) method and not outside.
If x would be an instance or class variable (static) then change(int ch) would change
The value of x and this change would be visible outside of method change because
There is a REFERENCE to an instance or to a class!!!

class CheckA20a { 
  public int y = 3; 
  public static void change(int ch){ 
    ch = 99; 
    System.out.println("x in change = "+ch);
  } 
  
  public static void main(String args[]) {
   int x=3; 
   System.out.println("Before change: x in main() = "+x);
   change(x);
   System.out.println("After change: x in main() = "+x);
  }
}

C:\Java\EigeneJavaProgramme>java CheckA20a
Before change: x in main() = 3
x in change = 99
After change: x in main() = 3

[Cindy Li]

Hi,
I think you might need to review these concepts.
1. member variable (or instance variable)
These are the variables your declare without 'static'. They can only be referred after you create a new instance.
In your main() code, you need to new A(), then call A.y=1; Otherwise, compiler throws error.
2. global variable (or class variable)
If you want to define global variable, you need to use 'static',
public class A{
public static int y;
...
Now you can call y from anywhere. y cab be referred with or without any instance of A. There is only one copy of y for all instances (if any).
Cindy