public with sharing class ClassFactory
{
    // Class Factory template
    public interface IClassFactory
    {
        void processWork();
    }

    // Class Factory base class
    public virtual class ClassFactoryBase
    {
        // ... Shared methods go here
    }


    // Process work
    public static void processAllWork()
    {
        ClassFactoryManager cfm = new ClassFactoryManager();
        cfm.newClassInstance('ClassFactory.Class1').processWork();
        cfm.newClassInstance('ClassFactory.Class2').processWork();
        cfm.newClassInstance('ClassFactory.Class3').processWork();
        cfm.newClassInstance('ClassFactory.Class4').processWork();
    }

    // Class1
    public class Class1 extends ClassFactoryBase implements IClassFactory
    {
        public void processWork()
        {
            // ... Class-specific work goes here
        }
    }

    // Class2
    public class Class2 extends ClassFactoryBase implements IClassFactory
    {
        public void processWork()
        {
            // ... Class-specific work goes here
        }
    }

    // Class3
    public class Class3 extends ClassFactoryBase implements IClassFactory
    {
        public void processWork()
        {
            // ... Class-specific work goes here
        }
    }

    // Class4
    public class Class4 extends ClassFactoryBase implements IClassFactory
    {
        public void processWork()
        {
            // ... Class-specific work goes here
        }
    }
}

public with sharing class ClassFactoryManager
{
    public ClassFactoryManager(){}

    // Return the appropriate class instance based on className
    public ClassFactory.IClassFactory newClassInstance(String className)
    {
        Type t = Type.forName(className);
        return (ClassFactory.IClassFactory) t.newInstance();
    }
}

> ToolingAPI x = new ToolingAPI(); ToolingAPI.ExecuteAnonymousResult
> toolingResult = x.executeAnonymousUnencoded("Your apex code as a
> string here");

public class Extension implements Callable {

   // Actual method
   String concatStrings(String stringValue) {
     return stringValue + stringValue;
   }

   // Actual method
   Decimal multiplyNumbers(Decimal decimalValue) {
     return decimalValue * decimalValue;
   }

   // Dispatch actual methods
   public Object call(String action, Map<String, Object> args) {
     switch on action {
       when 'concatStrings' {
         return this.concatStrings((String)args.get('stringValue'));
       }
       when 'multiplyNumbers' {
         return this.multiplyNumbers((Decimal)args.get('decimalValue'));
       }
       when else {
        throw new ExtensionMalformedCallException('Method not implemented');
       }
     }
   }

   public class ExtensionMalformedCallException extends Exception {}
}

@IsTest
private with sharing class ExtensionCaller {

   @IsTest
   private static void givenConfiguredExtensionWhenCalledThenValidResult() {

      // Given
      String className = 'Extension'; // Variable to demonstrate setting class name
      String methodName = 'multiplyNumbers'; // Variable to demonstrate setting method name
      Decimal decimalTestValue = 10;

      // When
      Callable extension = (Callable) Type.forName(className).newInstance();
      Decimal result = (Decimal) extension.call(methodName, new Map<String, Object> { 'decimalValue' => decimalTestValue });

      // Then
      System.assertEquals(100, result);
   }
}