Try to access static private attribute via ABAP RTTI and Java Reflection

In ABAP we can define a static attribute for a class via keyword CLASS-DATA, whose validity is not associated with instances of a class but with the class itself. In order to prove this fact I use the following simple Pointer class for demonstration:

class ZCL_POINT definition
  public
  final
  create public .
public section.

  data X type I .
  methods CONSTRUCTOR
    importing
      !IV_X type I
      !IV_Y type I .
private section.
  data Y type I .
  class-data COUNT type I .
ENDCLASS.
CLASS ZCL_POINT IMPLEMENTATION.
  method CONSTRUCTOR.
    me->x = iv_x.
    me->y = iv_y.
    count = count + 1.
  endmethod.
ENDCLASS.

In this class, static attribute count is responsible to maintain the number of created Point instances.
Then create four point instances:

data(a) = new zcl_point( iv_x = 1 iv_y = 1 ).
data(b) = new zcl_point( iv_x = 1 iv_y = 2 ).
data(c) = new zcl_point( iv_x = 1 iv_y = 3 ).
data(d) = new zcl_point( iv_x = 1 iv_y = 4 ).

Via any variable of a, b, c or d, we can monitor the value of count in debugger.

Can we access the static attribute of a class without object instance in debugger?

Since in theory the static attribute belongs to class instead of any dedicated object instance, so question comes: is there approach to monitor the static attribute value in ABAP debugger directly from class instead? Yes it is possible.

1. type text “{C:ZCL_POINT} in debugger and press enter key

2. double click, and you can see the attribute value is directly maintained in class ZCL_POINT, without any object instance created on top of it.

And I try to change its visibility dynamically via class descriptor via the following code and actually it is not possible:

data(lo) = CAST cl_abap_objectdescr( cl_abap_classdescr=>describe_by_name( 'ZCL_POINT' ) ).

read TABLE lo->attributes ASSIGNING FIELD-SYMBOL(<count>) WITH KEY name = 'COUNT'.

CHECK SY-SUBRC = 0.

<count>-visibility = 'U'.

Since the structure is read-only and not editable outside cl_abap_objectdescr.

This makes sense otherwise the encapsulation will be violated. Just check many other attribute marked as read-only in Class/Object descriptor class.

Reflection in Java

Check the following code which demonstrates how to access private static attribute value in code via Reflection.

import java.lang.reflect.Field;

public class Point {

private int x;

private int y;

static private int count = 0;

public Point(int x, int y){

this.x = x;

this.y = y;

count++;

}

private static void accessStaticPrivate(Point point){

Class classObject = point.getClass();

try {

Field countField = classObject.getDeclaredField("count");

System.out.println("count: " + countField.get(point));

} catch (NoSuchFieldException | SecurityException | IllegalArgumentException

| IllegalAccessException e1 ) {

e1.printStackTrace();

} 

}

public static void main(String[] arg){

Point a = new Point(1,2);

accessStaticPrivate(a);

Point b = new Point(1,3);

accessStaticPrivate(b);

Point c = new Point(1,4);

accessStaticPrivate(c);

Point d = new Point(1,5);

accessStaticPrivate(d);

}

}

For ABAPer it is easy to understand the usage of Class object in Java by just comparing it with CL_ABAP_CLASSDESCR in ABAP.

When running this small program locally, you will get output in console:

count: 1

count: 2

count: 3

count: 4