Oracle Certified Professional Java Se 11 Developer · Free Practice Question Medium
Question 89
Question ID: UKOCP35818
Consider below codes of 3 java files:
- //Buyable.java
- package com.udayankhattry.ocp;
- public interface Buyable {
- int salePercentage = 85;
- public static String salePercentage() {
- return salePercentage + "%";
- }
- }
- //Book.java
- package com.udayankhattry.ocp;
- public class Book implements Buyable {}
- //Test.java
- package com.udayankhattry.ocp;
- public class Test {
- public static void main(String[] args) {
- Buyable [] arr = new Buyable[2];
- for(Buyable b : arr) {
- System.out.println(b.salePercentage); //Line n1
- System.out.println(b.salePercentage()); //Line n2
- }
- Book [] books = new Book[2];
- for(Book b : books) {
- System.out.println(b.salePercentage); //Line n3
- System.out.println(b.salePercentage()); //Line n4
- }
- }
- }
Which of the following statements are correct?
Select 2 options.
- A There is a compilation error in Buyable.java file
- B There is a compilation error in Book.java file
- C There is a compilation error at Line n1
- D There is a compilation error at Line n2
- E There is a compilation error at Line n3
- F There is a compilation error at Line n4
Reveal correct answers
Correct answers: D, F
Explanation
UKOCP35818:
Variable 'salePercentage' declared inside interface Buyable is implicitly public, static and final. As per Java 8, default and static methods were added in the interface and as per Java 9, private methods were added in the interface. There is no compilation error in Buyable.java file.
class Book implements Buyable interface but as there is no abstract method in Buyable interface, hence Book class is not needed to implement any method. Book.java file compiles successfully.
Buyable [] arr = new Buyable[2]; creates one dimensional array of 2 elements of Buyable type and both the elements are initialized to null.
There are some difference in which static variables and static methods of the interface are accessed.
Correct and only way to access static method of an Interface is by using the name of the interface, such as Buyable.salePercentage(). Line n2 and Line n4 cause compilation error.
As far as public static final variable of interface is concerned, even through the correct way to access static variable is by using the name of the interface, such as Buyable.salePercentage but it can also be accessed by using following:
Reference variable of the interface: Buyable obj1 = null; System.out.println(obj1.salePercentage);
Name of the implementer class: System.out.println(Book.salePercentage);
Reference variable of the implementer class: Book obj2 = null; System.out.println(obj2.salePercentage);
Hence, Line n1 and Line n3 compile successfully.
Discussion
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