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

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

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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) }}

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

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JAVA Interfaces and Abstract Classes
What will be the output?interface A{public void method();}class One{public void method(){System.out.println("Class One method");}}class Two extends One implements A{public void method(){System.out.println("Class Two method");}}public class Test extends Two{public static void main(String[] args){A a = new Two();a.method();}}

None of these
Compilation Error
will print Class Two method
will print Class One method
compiles fine but print nothing

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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
A subclass can override a concrete method in a superclass to declare it abstract.
An abstract class can be extended.
A subclass of a non-abstract superclass can be abstract.

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