guava/src/com/google/common/reflect/TypeCapture.java
final Type capture() {
    Type superclass = getClass().getGenericSuperclass();
    checkArgument(superclass instanceof ParameterizedType, "%s isn't parameterized", superclass);
    return ((ParameterizedType) superclass).getActualTypeArguments()[0];
  }
final Type capture() {
    Type superclass = getClass().getGenericSuperclass();
    checkArgument(superclass instanceof ParameterizedType, "%s isn't parameterized", superclass);
    return ((ParameterizedType) superclass).getActualTypeArguments()[0];
  }
Returns the captured type.