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Accepted
D. Albarracín
Asked: 2020-07-20 12:07:20 +0800 CST 2020-07-20 12:07:20 +0800 CST

Problem with Abstract Class on OCA certification

  • 772

!Good!

I am studying, and preparing for the OCA Java 8 certification. There is a sample question that I don't quite understand... Which gives me this piece of code:

abstract class Writer {
 public static void write() {
 System.out.println("Writing...");
 }
}
class Author extends Writer {
 public static void write() {
 System.out.println("Writing book");
 }
}
public class Programmer extends Writer {
 public static void write() {
 System.out.println("Writing code");
 }
 public static void main(String[] args) {
 Writer w = new Programmer();
 w.write();
 }
}

And I have to choose the correct answer among these, to know what the result of the program would be:

A) Writing... B) Writing book C) Writing code D) Compilation fails.

According to the results provided by Oracle, the correct one would be A .

But why?

I thought it was C , but apparently not...

EDIT

I answer C , because maineven though a class object is being created in Writerit, a type is being stored Programmer, and therefore it should take the Writing code. Although it is true that the methods do not lead @override, but I did not know to what extent it can influence.

java

3 Answers

  1. Best Answer

    By creating an instance of Programmerand calling the method write(),

     Writer w = new Programmer();
 w.write();

    The class Programmerextends the class Writerwhich contains a static method, which in this case cannot be overloaded, so this will be the message to print.

    abstract class Writer {
    public static void write() {
        System.out.println("Writing...");
    }
}

    Departure:

    Writing...

    Therefore, the answer is A)

    In the case in which the methods write()were not static, the output would be

    Writing code

    the Author class is not used:

    class Author extends Writer {

    public static void write() {
        System.out.println("Writing book");
    }
}
    • 5

  2. The answer is A because if you look at the method writeit is static and when you call it with the type object you Writercall the static method of the class which would be the equivalent of writing

    Writer.write();
    • 4

  3. A) Because static methods cannot be overloaded.

    In Java, the binding is the association between the call of a method with the code of said method. There are two types of binding:

    • Static or Early, which is done at compile time. Static, private, and final methods are bound here.

    • Dynamic or Late, which occurs at runtime. The instance methods including the overrides are bound here.

    It cannot be C, because the compilation will not fail, however it would issue a Warning saying that the static methods must be called statically, that is, from the class and not from a class instance.

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