Question

is it possible to change the value of an attribute of a class using reflection.

below is my class :-

public class LoggerManager {

    private static LoggerManager _instance = new LoggerManager();

    private LoggerManager() {
    }

    public static LoggerManager getInstance() {
            return _instance; 
    }

    public Logger getLogger(String FQCN) {
        Logger logger =  Logger.getLogger(FQCN);
        logger.setLevel(Level.INFO);
        return logger;
    }
}

i want to change the value of _instance variable using reflection..

basically i want to change the value of the same to _instance = new NewLoggerManager();,

provided that NewLoggerManager extends LoggerManager

is it possible to do so, as i know how to invoke methods, but how to do this one.. ???

Answer 1

Field field = LoggerManager.class.getDeclaredField("_instance");
field.setAccessible(true);
field.set(null, new NewLoggerManager());

• the first line obtains the Field definition for the _instance field. Using the “declared” method, because it is able to obtain private fields as well
• setting the field to be accessible for reflective operations even if this would not be possible due to its visibility.
• setting a new object. Passing null as target object, because the field is static