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

When it makes sense to have objects of that class.
To prevent developers from further extending the class.
To force developers to extend the class not to use its capabilities.
When default implementations of some methods are not desirable.
When it doesn't make sense to have objects of that 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 keywords public and abstract cannot be used together.
Class School must be defined abstract.
The method numberOfStudent() in class School must have a body.
You must add a return statement in method numberOfStudent().

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JAVA Interfaces and Abstract Classes
Given the following piece of code:public interface Guard{ void doYourJob();}abstract public class Dog implements Guard{ }which of the following statements is correct?

This code will not compile, because method doYourJob() in interface Guard must be defined abstract.
This code will not compile, because class Dog must implement method doYourJob() from interface Guard.
This code will compile without any errors.
This code will not compile, because in the declaration of class Dog we must use the keyword extends instead of implements.

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

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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); }}

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

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