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Reflection generic get field value

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How do you find the value of field using reflection?

Field. get(Object obj) method returns the value of the field represented by this Field, on the specified object. The value is automatically wrapped in an object if it has a primitive type.

How do you set the value of a field of an object?

The set() method of java. lang. reflect. Field is used to set the value of the field represented by this Field object on the specified object argument to the specified new value passed as parameter.

What is Java Lang reflect field?

The java. lang. reflect. Field class provides information about, and dynamic access to, a single field of a class or an interface. The reflected field may be a class (static) field or an instance field.


Like answered before, you should use:

Object value = field.get(objectInstance);

Another way, which is sometimes prefered, is calling the getter dynamically. example code:

public static Object runGetter(Field field, BaseValidationObject o)
{
    // MZ: Find the correct method
    for (Method method : o.getMethods())
    {
        if ((method.getName().startsWith("get")) && (method.getName().length() == (field.getName().length() + 3)))
        {
            if (method.getName().toLowerCase().endsWith(field.getName().toLowerCase()))
            {
                // MZ: Method found, run it
                try
                {
                    return method.invoke(o);
                }
                catch (IllegalAccessException e)
                {
                    Logger.fatal("Could not determine method: " + method.getName());
                }
                catch (InvocationTargetException e)
                {
                    Logger.fatal("Could not determine method: " + method.getName());
                }

            }
        }
    }


    return null;
}

Also be aware that when your class inherits from another class, you need to recursively determine the Field. for instance, to fetch all Fields of a given class;

    for (Class<?> c = someClass; c != null; c = c.getSuperclass())
    {
        Field[] fields = c.getDeclaredFields();
        for (Field classField : fields)
        {
            result.add(classField);
        }
    }

You should pass the object to get method of the field, so

  Field field = object.getClass().getDeclaredField(fieldName);    
  field.setAccessible(true);
  Object value = field.get(object);

I use the reflections in the toString() implementation of my preference class to see the class members and values (simple and quick debugging).

The simplified code I'm using:

@Override
public String toString() {
    StringBuilder sb = new StringBuilder();

    Class<?> thisClass = null;
    try {
        thisClass = Class.forName(this.getClass().getName());

        Field[] aClassFields = thisClass.getDeclaredFields();
        sb.append(this.getClass().getSimpleName() + " [ ");
        for(Field f : aClassFields){
            String fName = f.getName();
            sb.append("(" + f.getType() + ") " + fName + " = " + f.get(this) + ", ");
        }
        sb.append("]");
    } catch (Exception e) {
        e.printStackTrace();
    }

    return sb.toString();
}

I hope that it will help someone, because I also have searched.


Although it's not really clear to me what you're trying to achieve, I spotted an obvious error in your code: Field.get() expects the object which contains the field as argument, not some (possible) value of that field. So you should have field.get(object).

Since you appear to be looking for the field value, you can obtain that as:

Object objectValue = field.get(object);

No need to instantiate the field type and create some empty/default value; or maybe there's something I missed.