OCPJP Simulation Test 102

102

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Question: What is the output of the following code?

  1 import java.util.function.*;

  2 public class Printing {

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

  4     Supplier<String> s1 = String::new;

  5     System.out.print(s1.get());

  6     Supplier<Integer> s2 = Integer::new;

  7     System.out.print(s2.get());}}

Choice:
A. no output
B. empty space followed by 0
C. 0
D. null0
E. nullnull
F. s1s2
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 4 declared a Supplier returns an object of type String. String::new is the function reference. Line 6 tries to defined a Supplier returns an object of type Integer. However, the error message is:

Printing.java:6: error: incompatible types: invalid constructor reference

    Supplier<Integer> s2 = Integer::new;

                           ^

    no suitable constructor found for Integer(no arguments)

        constructor Integer.Integer(int) is not applicable

          (actual and formal argument lists differ in length)

        constructor Integer.Integer(String) is not applicable

          (actual and formal argument lists differ in length)

Supplier functional interface defined the method get(), which is used to get the object supplied by the supplier.

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