Java OCA OCP Practice Question 2773

Question

Which of the following is true? 

4:    Stream<Integer> s = Stream.of(1); 
5:    IntStream is = s.mapToInt(x -> x); 
6:    DoubleStream ds = s.mapToDouble(x -> x); 
7:    Stream<Integer> s2 = ds.mapToInt(x -> x); 
8:    s2.forEach(System.out::print);
  • A. Line 4 does not compile.
  • B. Line 5 does not compile.
  • C. Line 6 does not compile.
  • D. Line 7 does not compile.
  • E. Line 8 does not compile.
  • F. The code throws an exception.
  • G. The code compiles and prints 1.


D.

Note

Line 4 should obviously look OK.

It creates a Stream and uses autoboxing to put the Integer 1 inside.

Line 5 converts to a primitive, again using autoboxing.

Line 6 converts to a double primitive, which works since double d = 1; would work.

Line 7 is where it all falls apart.

Converting from a double to an int would require a cast inside the lambda.




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