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Q:

What is the use of overriding?

Answer

- By using method overriding a sub class can change the definition of super class method.


- By using overriding a sub class can modify the functionality of the super class.

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Subject: Java

Q:

If sub class data member is hiding super class data member then how to access super class data member inside sub class methods?

Answer

use super keyword.


super keyword points immediate super class.


Class Sample {


int a =23;


 }


Class Sub extends Sample { 


 String a = "bablu";


 void show() {


 System.out.println(a); //bablu


 System. out. println(this.a); //bablu


 System. out.println(super.a); //23


}


}


Class Demo {


Public static void main(string[] args) {


sub s = new Sub();


s.show();


}


}


 

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Subject: Java

Q:

If super class ref is pointing sub class object then by using super class ref is it possible to call sub class newly defined method?

Answer

yes if the method is ovreriding method


no if the method is not overriding method

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Subject: Java

Q:

What is the use of super call?

Answer

By using super call we can call super class constructors  from sub class constructors and we can initialize super class private data.

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Subject: Java

Q:

What is JAR file? what are the main uses of JAR files?

Answer

JAR files are java's version of ZIP files. In fact, JAR uses the ZIP file format.


uses:


- to compress a number of . class files into one file


- to make a java executable JAR file.

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Subject: Java

Q:

What is unwrapping?

Answer

Unwrapping is also called as unpacking or unboxing.


Getting the private data stored in the object by using methods is called unpacking or unwrapping.

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Subject: Java

Q:

What is different among String, StringBuffer, StringBuilder?

Answer

String class objects are immutable objects and they represents strings( sequence of characters)


StringBuffer class objects are mutable objects representing strings and they are Thread safe


StringBuild class objects are also mutable objects representing strings and they are not Thread safe

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Subject: Java

Q:

How to call argument constructor?

Answer

new ClassName( arg1, arg2, .... argN);


Ex:


Class sample {


   Sample(int a) {


   System.out.println("arg con a =" +a);


   }


}


class Demo {


    Public static void main( String[] args) {


     Sample s1= new Sample(23);


     Sample s2= new Sample(45);


    }


}

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Subject: Java