/**
 * Scope.java -- Illustrate Java variables and scope rules
 *
 * @author  J. Jacky
 * @version 6-Apr-2001 Written
 */

import java.io.*;  // needed for println

// Each file must contain one public class, with the same name as the file
public class Scope {
    
    // Class variables are like global variables.  
    // They are declared with the static modifier
    public static int x = 1;  // you can initialize variables in declarations
    public static int y = 2;

    // Class methods are like functions, also must be declared static
    public static int sum(int a, int b, int c) {
	return a + b + c;
    }

    // We can define our own println method for this class
    public static void println(int x, int y, int z, int s) {
	// Java automatically converts variables to strings in this context
	// Between strings + is concatentation, between numbers + is addition
	System.out.println(" x " + x + "  y " + y + "  z " + z + "   s " + s);
    }	

    // The main method in the class runs when you execute "java <classname>"
    public static void main(String args[]) {
	// Local variables are declared within methods
	int y = 3;
	int z = 4;
	int s;

	System.out.print("Scope.main, global x, local y, local z : ");
	s = sum(x,y,z); println(x,y,z,s);

	System.out.print("Scope.main, global x, global y, local z: ");
	s = sum(x,Scope.y,z); println(x,Scope.y,z,s);
	
	// Call the aux method and pass the local y, then again with global y
	// \n is newline, forces linebreak
	System.out.println("\nmain passes local y to aux: "); aux(y);
	System.out.println("\nmain passes global y to aux: "); aux(Scope.y);

	// Call the aux method in the Other class
	System.out.println("\nmain passes local y to Other.aux: "); 
	Other.aux(y);
	System.out.println("\nmain passes global y to Other.aux: ");
	Other.aux(Scope.y);
	System.out.println("\nmain passes Other.y to Other.aux: ");
	Other.aux(Other.y);
    }

    public static void aux(int y) {
	int z = 5;
	System.out.print("Scope.aux, global x, passed y, local z : ");
	int s = sum(x,y,z); println(x,y,z,s);
    }
}

// You can put several classes in a file, but only one can be public
class Other {
    public static int x = 6; 
    public static int y = 7;
    
    public static void aux(int y) {
	int z = 8;
	System.out.print("Other.aux, global x, passed y, local z : ");
	
	// call methods in another class
	int s = Scope.sum(x,y,z); Scope.println(x,y,z,s);
    }	
}

---------------------------------------------------------------------------

$ java Scope
Scope.main, global x, local y, local z :  x 1  y 3  z 4   s 8
Scope.main, global x, global y, local z:  x 1  y 2  z 4   s 7
 
main passes local y to aux:
Scope.aux, global x, passed y, local z :  x 1  y 3  z 5   s 9
 
main passes global y to aux:
Scope.aux, global x, passed y, local z :  x 1  y 2  z 5   s 8
 
main passes local y to Other.aux:
Other.aux, global x, passed y, local z :  x 6  y 3  z 8   s 17
 
main passes global y to Other.aux:
Other.aux, global x, passed y, local z :  x 6  y 2  z 8   s 16
 
main passes Other.y to Other.aux:
Other.aux, global x, passed y, local z :  x 6  y 7  z 8   s 21