Enthuware

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Given that Book is a valid class with appropriate constructor and getPrice and getTitle methods that returns a double and a String respectively, consider the following code:  
List<List<Book>> bs = Arrays.asList(
         Arrays.asList(
                 new Book("Windmills of the Gods", 7.0),
                 new Book("Tell me your dreams",9.0) ),
         Arrays.asList(
                 new Book("There is a hippy on the highway", 5.0),
                 new Book("Easy come easy go", 5.0)) );
  double d = allbooks.stream()
         INSERT CODE HERE //1
         INSERT CODE HERE //2
         .sum(); System.out.println(d);
  What can be inserted in the above code so that it will print 26.0?

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List<List<Book>> bs = Arrays.asList( ...
double d = bs.stream().flatMap(bs -> bs.stream()).mapToDouble(book -> book.getPrice());

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double d = bs.stream().flatMap(ss -> ss.stream()).mapToDouble(book -> book.getPrice());