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); }}

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

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

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

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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(); }}

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

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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.
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.

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

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