Java toString() using reflection?

Question

I was writing a toString() for a class in Java the other day by manually writing out each element of the class to a String and it occurred to me that using reflection it might be possible to create a generic toString() method that could work on ALL classes. I.E. it would figure out the field names and values and send them out to a String.

Getting the field names is fairly simple, here is what a co-worker came up with:

public static List initFieldArray(String className) throws ClassNotFoundException {

    Class c = Class.forName(className);
    Field field[] = c.getFields();
    List<String> classFields = new ArrayList(field.length);

    for (int i = 0; i < field.length; i++) {
        String cf = field[i].toString();
        classFields.add(cf.substring(cf.lastIndexOf(".") + 1));
    }

    return classFields;
}

Using a factory I could reduce the performance overhead by storing the fields once, the first time the toString() is called. However finding the values could be a lot more expensive.

Due to the performance of reflection this may be more hypothetical then practical. But I am interested in the idea of reflection and how I can use it to improve my everyday programming.

Answer 1

Apache commons-lang ReflectionToStringBuilder does this for you.

import org.apache.commons.lang3.builder.ReflectionToStringBuilder

// your code goes here

public String toString() {
   return ReflectionToStringBuilder.toString(this);
}