JAVA Interfaces and Abstract Classes
Which of the following is a correct interface?

abstract interface A { print(); }
abstract interface A { abstract void print(); { }}
interface A { void print() { } }
interface A { void print(); }

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JAVA Interfaces and Abstract Classes
Which of the following statements regarding abstract classes are true?

A subclass of a non-abstract superclass can be abstract.
An abstract class can be used as a data type.
An abstract class can be extended.
A subclass can override a concrete method in a superclass to declare it abstract.
All of these

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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();}}

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

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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"); }}

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

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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 method doYourJob() in interface Guard must be defined abstract.
This code will not compile, because class Dog must implement method doYourJob() from interface Guard.
This code will not compile, because in the declaration of class Dog we must use the keyword extends instead of implements.

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