JAVA Interfaces and Abstract Classes
Which of the following class definitions defines a legal abstract class?

class A { abstract void unfinished() { } }
abstract class A { abstract void unfinished(); }
class A { abstract void unfinished(); }
public class abstract A { abstract void unfinished(); }

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JAVA Interfaces and Abstract Classes
What is the output for the below code ?interface A{ public void printValue();}1. public class Test{2. public static void main (String[] args){3. A a1 = new A(){4. public void printValue(){5. System.out.println("A");6. }7. };8. a1.printValue();9. }10. }

A
Compilation fails due to an error on line 8
null
Compilation fails due to an error on line 3
None of these

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JAVA Interfaces and Abstract Classes
What will be the output?1. public interface InfA{2. protected String getName();3. }public class Test implements InfA{ public String getName(){ return "test-name"; } public static void main (String[] args){ Test t = new Test(); System.out.println(t.getName()); }}

Compilation succeed but Runtime Exception
Compilation fails due to an error on lines 1
None of these
test-name
Compilation fails due to an error on lines 2

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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();}}

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

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

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