If you have 30 fields named test1 through test30, you might want to consider using an array, and naming your fields test[1]-test[30] (or test[0]-test[29]). If you really want dynamic naming, you could use reflection as follows (I am using doubles in this example):

import java.lang.reflect.Field;

public class YourClass {
 double test1;
 double test2;
 ...
 public void yourMethod () {
  ...
  for (int i=1; i<=30; i++}
   Field f = this.getClass().getDeclaredField("test"+i);
   field.setDouble(this,someValue);
  }
 }
}

Note that the reflection methods throw various exceptions that I am not bothering to catch here, and that there is considerable flexibility in the Field class to manipulate values of other than double fields.