Java generics confusion

GenericsTest.java

import org.junit.Test;

import java.util.Arrays;
import java.util.List;


public class GenericsTest {

  @Test
  public void should_convert___well_huh() throws Exception {
    List<Double> list = Arrays.asList(12.0, 3.0);

    List<String> result = convert(list);

    for (Object s : result) {
      final Double value = (Double) s;
      System.out.println(value);
      // no compilation error, print 12.0 3.0
    }
  }

  <T> List<T> convert(List l) {
    return l;
  }

}

in the inner loop if you use String instead of Object and then remove the cast to Double,
you'll get a ClassCastException