JAVA Interfaces and Abstract Classes
In Java, declaring a class abstract is useful

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

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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
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
Compilation error as class can not be declared as abstract.
Program will compile and execute successfully and prints
Program compiles but leads to runtime exception.
Compilation error occurs as the abstract class TestAbstract contains a non-abstract method.

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

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

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