Question

Suppose you have a text file like:

my_setting = ON
some_method = METHOD_A
verbosity = DEBUG
...

That you wish to to update a corresponding object accordingly:

Setting my_setting = ON;
Method some_method = METHOD_A;
Verbosity verbosity = DEBUG;
...

Where all are different kind of enums.

I would like to have a generic way to instantiate the enum values. That is, at runtime using reflection, and without knowing the enum types of the object in advance.

I would have imagined something like this:

for (ConfigLine line : lines)
{
   String[] tokens = line.string.split("=", 2);
   String name = tokens[0].trim();
   String value = tokens[1].trim();

   try
   {
      Field field = this.getClass().getDeclaredField(name);   
      if(field.getType().isEnum())
      {
         // doesn't work (cannot convert String to enum)
         field.set(this, value);
         // invalid code (some strange generics issue)
         field.set(this, Enum.valueOf(field.getType().getClass(), value));
      }
      else
      { /*...*/ }
   }
   catch //...
}

The question is: what should there be instead? Is it even possible to instantiate an unknown enum given its String representation?

Answer 1

field.set(this, Enum.valueOf((Class<Enum>) field.getType(), value));

• getClass() after getType() should not be called – it returns the class of a Class instance
• You can cast Class<Enum>, to avoid generic problems, because you already know that the Class is an enum