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) }}

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

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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(); }}

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

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

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

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

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.
To prevent developers from further extending the class.
When it makes sense to have objects of that class.

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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 class Dog must implement method doYourJob() from interface Guard.
This code will compile without any errors.
This code will not compile, because method doYourJob() in interface Guard must be defined abstract.
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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