JAVA Interfaces and Abstract Classes
What will be the output when the following program is compiled and executed?abstract class TestAbstract{ String my_name; String myName(){ my_name = "Examveda"; return my_name; } abstract void display();}public class Test extends TestAbstract{ void display(){ String n = myName(); System.out.print("My name is "+ n); } public static void main(String args[]){ Test t = new Test(); t.display(); }}

None of these
Program will compile and execute successfully and prints
Program compiles but leads to runtime exception.
Compilation error as class can not be declared as abstract.
Compilation error occurs as the abstract class TestAbstract contains a non-abstract method.

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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 not compile, because method doYourJob() in interface Guard must be defined abstract.
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 class Dog must implement method doYourJob() from interface Guard.
This code will compile without any errors.

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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"); }}

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
In Java, declaring a class abstract is useful

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

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