What is reflection, and why is it useful?
I\'m particularly interested in Java, but I assume the principles are the same in any language.
I just want to add some point to all that was listed.
With Reflection API you can write universal toString() method for any object.
toString()
It is useful at debugging.
Here is some example:
class ObjectAnalyzer { private ArrayList visited = new ArrayList(); /** * Converts an object to a string representation that lists all fields. * @param obj an object * @return a string with the object's class name and all field names and * values */ public String toString(Object obj) { if (obj == null) return "null"; if (visited.contains(obj)) return "..."; visited.add(obj); Class cl = obj.getClass(); if (cl == String.class) return (String) obj; if (cl.isArray()) { String r = cl.getComponentType() + "[]{"; for (int i = 0; i < Array.getLength(obj); i++) { if (i > 0) r += ","; Object val = Array.get(obj, i); if (cl.getComponentType().isPrimitive()) r += val; else r += toString(val); } return r + "}"; } String r = cl.getName(); // inspect the fields of this class and all superclasses do { r += "["; Field[] fields = cl.getDeclaredFields(); AccessibleObject.setAccessible(fields, true); // get the names and values of all fields for (Field f : fields) { if (!Modifier.isStatic(f.getModifiers())) { if (!r.endsWith("[")) r += ","; r += f.getName() + "="; try { Class t = f.getType(); Object val = f.get(obj); if (t.isPrimitive()) r += val; else r += toString(val); } catch (Exception e) { e.printStackTrace(); } } } r += "]"; cl = cl.getSuperclass(); } while (cl != null); return r; } }
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