Is it possible to link integers from a method to a class?

Question

I have a quick question out of curiosity...if I declare an integer in one method, for example: i = 1, is it possible for me to take that i and use its value in my main class (or another method)? The following code may be helpful in understanding what I'm asking...of course, the code might not be correct depending on what the answer is.

public class main {
  public main() {
    int n = 1;
    System.out.print(n + i);
  }

  public number(){
    i = 1;
  }
}

Answer 1

You may use a class-scope field to store you variable in a class object or you can return it from one method or pass it as a parameter to the other. Mind that you will need to call your methods in the right order, which is not the best design possible.

public class main {

  int n;
  int i;
  public main() {
    n = 1;
    System.out.print(n + i);
  }

  public number(){
    i = 1;
  }
}

Answer 2

No you cannot! Not unless you make it an instance variable!

Or actually send it to the function as an argument!

Answer 3

First, let's start simple. All methods that are not constructors require a return type. In other words,

 public void number(){
     i = 1;
 }

would be more proper.

Second: the main method traditionally has a signature of public static void main(String[] args).

Now, on to your question at hand. Let's consider a few cases. I will be breaking a few common coding conventions to get my point across.

Case 1

 public void number(){
    i = 1;
 }

As your code stands now, you will have a compile-time error because i is not ever declared. You could solve this by declaring this somewhere in the class. To access this variable, you will need an object of type Main, which would make your class look like this:

public class Main {
    int i;

    public static void main(String[] args) {
        Main myMain = new Main();
        myMain.number();
        System.out.print(myMain.i);
    }

    public void number(){
        i = 1;
    }
}

Case 2

Let's say you don't want to make i a class variable. You just want it to be a value returned by the function. Your code would then look like this:

public class Main {

    public static void main(String[] args) {
        Main myMain = new Main();
        System.out.print(myMain.number());
    }

    public int number(){  //the int here means we are returning an int
        i = 1;
        return i;
    }
}

Case 3

Both of the previous cases will print out 1 as their output. But let's try something different.

public class Main {
    int i = 0;

    public static void main(String[] args) {
        Main myMain = new Main();
        myMain.number();
        System.out.print(myMain.i);
    }

    public void number(){
        int i = 1;
    }
}

What do you think the output would be in this case? It's not 1! In this case, our output is 0. Why?

The statement int i = 1; in number(), it creates a new variable, also referred to as i, in the scope of number(). As soon as number() finishes, that variable is wiped out. The original i, declared right under public class Main has not changed. Thus, when we print out myMain.i, its value is 0.

Case 4

One more case, just for fun:

public class Main {
    int i = 0;

    public static void main(String[] args) {
        Main myMain = new Main();
        System.out.print(myMain.number());
        System.out.print(myMain.i);
    }

    public int number(){
        int i = 1;
        return i;
    }
}

What will the output of this be? It's 10. Why you ask? Because the i returned by number() is the i in the scope of number() and has a value of 1. myMain's i, however, remains unchanged as in Case 3.

Answer 4

Yes, create a classmember:

public class Main
{
  private int i;

  public main() {
    int n = 1;
    System.out.print(n + i);
    number();
    System.out.print(n + i);
  }

  public number(){
    i = 1;
  }
}

Answer 5

void method(){
   int i = 0; //has only method scope and cannot be used outside it
}

void method1(){
   i = 1; //cannot do this
}

This is because the scope of i is limited to the method it is declared in.