OCPJP Simulation Test 89

89

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Question: What is the output of the following code?

  1 import java.util.function.*;

  2 import java.util.*;

  3 public class Printing {

  4   public static void main(String...args) {

  5     Supplier<Set<String>> s1 = HashSet<>::new;

  6     System.out.print(s1.get());

  7     s1 = () -> new HashSet<String>();

  8     System.out.print(s1.get());

  9     Supplier<Map<Integer, String>> s2 = TreeMap::new;

 10     System.out.print(s2.get());}}

Choice:
A. program print nothing
B. HashSetHashSetHashMap
C. SetSetMap
D. [][]{}
E. two space followed by {}
F. three empty space
G. code does not compile
H. code compiles but throw runtime exceptions.



Next Question

Answer: G

Explain: Supplier functional interface takes no parameter, returns an object of the defined type. Line 5 declared a Supplier returns an object of type Set<String>. HashSet<String>::new and () -> new HashSet<String>() are method reference and corresponding lambda function. However HashSet<>::new is wrong syntax, the error is: Printing.java:5: error: illegal start of type . Line 9 defined a Supplier returns an object of type Map<Integer, String>. Supplier functional interface defined the method get(), which is used to get the object supplied by the supplier. An empty HashSet<String> print a [], an empty HashMap<Integer, String> print a {}.

Study:  Use  the built-in interfaces included in the java.util.function package such as Predicate, Consumer, Function, and Supplier   

Create and use ArrayList, TreeSet, TreeMap, and ArrayDeque objects

Use method references with Streams