JAVA Interfaces and Abstract Classes
Determine output of the following code.interface A { }class C { }class D extends C { }class B extends D implements A { }public class Test extends Thread{ public static void main(String[] args){ B b = new B(); if (b instanceof A) System.out.println("b is an instance of A"); if (b instanceof C) System.out.println("b is an instance of C"); }}

b is an instance of
b is an instance of
b is an instance of A followed by b is an instance of
Nothing.

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JAVA Interfaces and Abstract Classes
Given the following piece of code:public interface Guard{ void doYourJob();}abstract public class Dog implements Guard{ }which of the following statements is correct?

This code will compile without any errors.
This code will not compile, because in the declaration of class Dog we must use the keyword extends instead of implements.
This code will not compile, because method doYourJob() in interface Guard must be defined abstract.
This code will not compile, because class Dog must implement method doYourJob() from interface Guard.

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JAVA Interfaces and Abstract Classes
In Java, declaring a class abstract is useful

When default implementations of some methods are not desirable.
To prevent developers from further extending the class.
When it makes sense to have objects of that class.
When it doesn't make sense to have objects of that class.
To force developers to extend the class not to use its capabilities.

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JAVA Interfaces and Abstract Classes
What will be the output?interface A{public void method();}class One{public void method(){System.out.println("Class One method");}}class Two extends One implements A{public void method(){System.out.println("Class Two method");}}public class Test extends Two{public static void main(String[] args){A a = new Two();a.method();}}

compiles fine but print nothing
Compilation Error
will print Class One method
None of these
will print Class Two method

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