JAVA Interfaces and Abstract Classes
What will be the output for the below code ?public interface TestInf{ int i =10;}public class Test{ public static void main(String... args){ TestInf.i=12; System.out.println(TestInf.i); }}

None of these
12
10
Compile with error
Runtime Exception

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JAVA Interfaces and Abstract Classes
What will happen after compiling this program code?abstract class MyClass{ //line 1 private int a, b; public void call(int a, int b){ this.a = a; this.b = b; System.out.print(a+b); }}public class Test{ public static void main(String args[]){ MyClass m = new MyClass(); //line 2 m.call(12,25); }}

Runtime error
None of these
Compilation error due to line 1
Compilation error due to line 2
Successful run and print 37

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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.
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.
To prevent developers from further extending the class.

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

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JAVA Interfaces and Abstract Classes
Given the following piece of code:public class School{ public abstract double numberOfStudent();}which of the following statements is true?

The method numberOfStudent() in class School must have a body.
You must add a return statement in method numberOfStudent().
Class School must be defined abstract.
The keywords public and abstract cannot be used together.

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

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

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