Parametrize the usage of static variables in an abstract class

Question

I am generating a report for a customer of our company.

I have a abstract class with lots of static final int members:

public abstract class Customer_ItemIDs {
   public static final int item_001 = 34535;
   public static final int item_002 = 23455;
   public static final int item_003 = 74565;
   public static final int item_004 = 83480;
   ...
   public static final int item_122 = 65487;

}

In my class where I generate my report I use them like this (simplified a bit):

int itemID_004;
itemID_004 = Customer_ItemIDs.item_004;

Now there is a change in the requirement.

I need to support another Customer with totally different ItemIDs which i want to put in another static class. The name of the items stay the same, just the values are different.

public abstract class CustomerB_ItemIDs {
   public static final int item_001 = 17538;
   public static final int item_002 = 56756;
   public static final int item_003 = 94445;
   public static final int item_004 = 93757;
   ...
   public static final int item_122 = 69483;

}

How do I properly parametrize this, without changing every line of code where I initialize my itemIDs? I don't want to initialize the itemIDs like this:

int itemID_004;
if (customer == customerA) {
   itemID_004 = CustomerA_itemIDs.item_004;
}
else if (customer == customerB) {
   itemID_004 = CustomerB_itemIDs.item_004;
}

I would like to change as little as possible.

Answer 1

I think you should try Java Reflections: java.lang.reflect

To not to interrupt the existing classes source code, I would create a method which will return HashMap with all field's name as a key and its int values as value, using provided class name as a parameter:

public static Map<String, Integer> getStaticVariablesValue(Class givenClass) {
    
    Field[] fields = givenClass.getDeclaredFields();
    Map<String, Integer> resultValues = new HashMap<>();
    
    for (int i = 0; i < fields.length; i++)
        if (fields[i].getType() == int.class)
            try {
                resultValues.put(fields[i].getName(), fields[i].getInt(null));
            } catch (IllegalAccessException e) {
                e.printStackTrace(System.out);
            }
            
    return resultValues;
    
}

Here is simple example, which will print you all fields with values for provided Class:

import java.util.*;
import java.lang.reflect.*;

class Main {
    public static void main(String args[]) {
        
        Map<String, Integer> customer_ItemIDsValues = new HashMap<>();
        Map<String, Integer> customerB_ItemIDsValues = new HashMap<>();

        customer_ItemIDsValues = getStaticVariablesValue(Customer_ItemIDs.class);
        customerB_ItemIDsValues = getStaticVariablesValue(CustomerB_ItemIDs.class);
        
        //Output values to console
        for (Map.Entry<String, Integer> entry : customer_ItemIDsValues.entrySet()) {
            System.out.println(entry.getKey() + " = " + entry.getValue());
        }
            
        for (Map.Entry<String, Integer> entry : customerB_ItemIDsValues.entrySet()) {
            System.out.println(entry.getKey() + " = " + entry.getValue());
        }
    }
    
    public static Map<String, Integer> getStaticVariablesValue(Class givenClass) {
        
        Field[] fields = givenClass.getDeclaredFields();
        Map<String, Integer> resultValues = new HashMap<>();
        
        for (int i = 0; i < fields.length; i++)
            if (fields[i].getType() == int.class)
                try {
                    resultValues.put(fields[i].getName(), fields[i].getInt(null));
                } catch (IllegalAccessException e) {
                    e.printStackTrace(System.out);
                }
                
        return resultValues;
    }

    abstract class CustomerB_ItemIDs {
       public static final int item_001 = 17538;
       public static final int item_002 = 56756;
       public static final int item_003 = 94445;
       public static final int item_004 = 93757;
       public static final int item_122 = 69483;
    }

    class Customer_ItemIDs {
       public static final int item_001 = 34535;
       public static final int item_002 = 23455;
       public static final int item_003 = 74565;
       public static final int item_004 = 83480;
       public static final int item_122 = 65487;
    }
}