Interview Questions

array_flip exchange the keys with their associated values in array ie. Keys becomes values and values becomes keys.

<?php
$arrayName    = array("course1"=>"php","course2"=>"html");
$new_array    = array_flip($arrayName);
print_r($new_array);
?>

OUTPUT :

Array
(
[php]     => course1
[html]    => course2
)

Wrapping is also called as packing or boxing.

Storing the data inside the object as private data which can accessed outside the class only by using methods.

we can override tostring() method to return String representation of our object data

Primary key constraint ensures that the column(s) always has a unique value to identify the record.
Example:
Below, the primary key is created for column id with name prim_id.
create table employee ( id number NOT NULL, Name varchar(200) Constraint prim_id primary key(id) );

1.Main difference is methods of a Java interface are implicitly abstract and cannot have implementations. A Java abstract class can have instance methods that implements a default behavior.

2.Variables declared in a Java interface is by default final. An abstract class may contain non-final variables.

3.Members of a Java interface are public by default. A Java abstract class can have the usual flavors of class members like private, protected, etc..

4.Java interface should be implemented using keyword “implements”; A Java abstract class should be extended using keyword “extends”.

5.An interface can extend another Java interface only, an abstract class can extend another Java class and implement multiple Java interfaces.

6.A Java class can implement multiple interfaces but it can extend only one abstract class.

7.Interface is absolutely abstract and cannot be instantiated; A Java abstract class also cannot be instantiated, but can be invoked if a main() exists.

8.In comparison with java abstract classes, java interfaces are slow as it requires extra indirection.

Whenever there is local- variable/parameter inside the method with same name as data member.

Ex:

Class Sample {

 int a;

  void show() {

   int a=5;

   system.out.println(a); // 5

   system.out.println(this.a);//23

  }

}

class MainApp {

  Public static void main(String[] args) {

  Sample s = new Sample();

   s.a = 23;

   s.show();

   }

}

the layer that establishes ,manages and terminates the session between two communticating devices