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

To prevent developers from further extending the 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.
When it makes sense to have objects of that class.
When default implementations of some methods are not desirable.

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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()); }}

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

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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); }}

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

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

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JAVA Interfaces and Abstract Classes
interface Base{ boolean m1 (); byte m2(short s);}which two code fragments will compile?1. interface Base2 implements Base {}2. abstract class Class2 extends Base { public boolean m1(){ return true; }}3. abstract class Class2 implements Base {}4. abstract class Class2 implements Base { public boolean m1(){ return (7 > 4); }}5. abstract class Class2 implements Base { protected boolean m1(){ return (5 > 7) }}

4 and 5
2 and 3
1 and 2
3 and 4
1 and 3

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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?

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

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