import java.util.ArrayList;
import java.util.List;


public class GenericsTest {

    public static void main(String args) {
        Field<String> f1 = new Field<String>("test");
        Field<Integer> f2 = new Field<Integer>(1);
        Field<Long> f3 = new Field<Long>(1l);
        
        List<Field<?>> fields = new ArrayList<Field<?>>();
        fields.add(f1);
        fields.add(f2);
        fields.add(f3);

        for (Field<?> field : fields) {
            Object value = field.getValue();
            // Compilation error! Expects specific type.
            field.doSomething(value);
        }
    }
    
    private static class Field<T> {
        private final T value;

        public Field(T value) {
            super();
            this.value = value;
        }
        
        public T getValue() {
            return value;
        }
   
        public void doSomething(T val) {
            System.out.println("Value: " + val);
        }
    }
}

    ...
    for (Field field : fields) {
    ...

public class A<T>{
}