Java String value as part of statement?

Question

I have a class declared to hold information. Let's say it has these fields

class data {
   int a;
   int b;
   int c;
}

And I want to access these fields like this:

String [] fields = {"a", "b", "c"};
data da = new data();
for (int i = 0; i < 3; i++) 
   if (da.fields[i] < 10)
      dosomething();

Is there any way in Java to do this? Googling, I got some results about something called "reflection, " but I've never really heard of that, and I don't think it's quite what I want. Is there any way to do this in Java? If not, are there any languages that support this kind of thing (just out of curiosity)?

Answer 1

Reflection is probably what you need. But what you need more is a hard look at your design. You should avoid reflection where possible.

If you are still interested in doing this, take a look at Java Reflection: Fields.

Field field = aClass.getField("someField");

Is what you would do to get the field by that name. A more detailed example of what you want.

Class  aClass = MyObject.class
Field field = aClass.getField("someField");

MyObject objectInstance = new MyObject();

Object value = field.get(objectInstance);

field.set(objetInstance, value);

Answer 2

You could add a suitable API to your class:

class data {
   int a;
   int b;
   int c;

   int get(String field) {
       if (field.equals("a")) return a;
       if (field.equals("b")) return b;
       if (field.equals("c")) return c;
       throw new IllegalArgumentException();
   }
}

Then you could:

String [] fields = {"a", "b", "c"};
data da = new data();
for (int i = 0; i < 3; i++) 
   if (da.get(fields[i]) < 10)
      dosomething();