CSC300: Extras: Scope [12/12]

def declareX():
    global x
    x = 0

def useX():
    x 

useX() # runtime error
declareX()
useX() # no problems  

package algs11;
import stdlib.*;
public class Hello {
  public static void declareX () {
    int x;
  }
  public static void useX () {
    x;  // compiler error
  }    
  public static void main (String[] args) {
    useX ();
    declareX ();
    useX ();
  }
}

Java compiler removes names for variables. Only the values are stored at runtime. The variable names are replaced with numbers (offsets in memory). This is one characteristic of static languages.

Python keeps names for variables at runtime. It stores a map (aka, a dictionary) from variable names to values. This is characteristic of dynamic languages.

Java's approach is more efficient. Python's is more flexible.

Scripting languages, such as perl and javascript, use the python approach. Most other languages, including C, C++, C#, objective-C, swift and FORTRAN, use the java approach.