knowledgebase: interview-qn2

Program to check if String is palindrome

import java.util.*;
 
class Palindrome
{
  public static void main(String args[])
  {
    String inputString;
    Scanner in = new Scanner(System.in);
 
    System.out.println("Input a string");
    inputString = in.nextLine();
 
    int length  = inputString.length();
    int i, begin, end, middle;
 
    begin  = 0;
    end    = length - 1;
    middle = (begin + end)/2;
 
    for (i = begin; i <= middle; i++) {
      if (inputString.charAt(begin) == inputString.charAt(end)) {
  begin++;
  end--;
   }
      else {
     break;
      }
    }
    if (i == middle + 1) {
      System.out.println("Palindrome");
    }
    else {
      System.out.println("Not a palindrome");
    }  
  }
}

Program to reverse a string

new StringBuilder(“meeraja”).reverse().toString();

String s = "sample";

String result = new StringBuffer(s).reverse().toString();

import java.util.*;

class ReverseString

   public static void main(String args[])

      String original, reverse = "";

      Scanner in = new Scanner(System.in);

      System.out.println("Enter a string to reverse");

      original = in.nextLine();

      int length = original.length();

      for ( int i = length - 1 ; i >= 0 ; i-- )

         reverse = reverse + original.charAt(i);

      System.out.println("Reverse of entered string is: "+reverse);

Program to implement a LinkList

import java.util.*;

public class LinkedListDemo {

   public static void main(String args[]) {

      // create a linked list

      LinkedList ll = new LinkedList();

      // add elements to the linked list

      ll.add("F");

      ll.add("B");

      ll.add("D");

      ll.add("E");

      ll.add("C");

      ll.addLast("Z");

      ll.addFirst("A");

      ll.add(1, "A2");

      System.out.println("Original contents of ll: " + ll);

      // remove elements from the linked list

      ll.remove("F");

      ll.remove(2);

      System.out.println("Contents of ll after deletion: "

       + ll);

      // remove first and last elements

      ll.removeFirst();

      ll.removeLast();

      System.out.println("ll after deleting first and last: "

       + ll);

Program to open a file and write or read something in file using java

import java.io.*;

public class FileRead{

   public static void main(String args[])throws IOException{

      File file = new File("Hello1.txt");

      // creates the file

      file.createNewFile();

      // creates a FileWriter Object

      FileWriter writer = new FileWriter(file);

      // Writes the content to the file

      writer.write("This\n is\n an\n example\n");

      writer.flush();

      writer.close();

      //Creates a FileReader Object

      FileReader fr = new FileReader(file);

      char [] a = new char[50];

      fr.read(a); // reads the content to the array

      for(char c : a)

          System.out.print(c); //prints the characters one by one

      fr.close();

Questions on Hashmap

HashMap works on the principle of hashing

put(key, value): HashMap stores both key and value object as Map.Entry. Hashmap applies hashcode(key) to get the bucket. if there is collision ,HashMap uses LinkedList to store object.

get(key): HashMap uses Key Object's hashcode to find out bucket location and then call keys.equals() method to identify correct node in LinkedList and return associated value object for that key in Java HashMap

Difference between equals and ==

In Java, when the “==” operator is used to compare 2 objects, it checks to see if the objects refer to the same place in memory

String obj1 = new String("xyz");

String obj2 = new String("xyz");

if(obj1 == obj2)

   System.out.println("obj1==obj2 is TRUE");

else

  System.out.println("obj1==obj2 is FALSE");

o/p false

String obj1 = new String("xyz");

String obj2 = obj1;

if(obj1 == obj2)

   System.out.println("obj1==obj2 is TRUE");

else

  System.out.println("obj1==obj2 is FALSE");

o/p true

String obj1 = new String("xyz");

String obj2 = new String("xyz");

if(obj1.equals(obj2))

   System.out.printlln("obj1==obj2 is TRUE");

else

  System.out.println("obj1==obj2 is FALSE");

Output true

Questions on Design patterns
Strategy and State design Pattern,singleton,etc

Design patterns are useful because they provide a pre-formulated solution to problems based on the experience of other programmers. This can save you a lot of time.

how to solve a problem in different situations.

Singleton pattern is one of the design patterns that is utilized for restricting instantiation of a class to one or few specific objects................

Process pattern: Methods, best practices, techniques for developing an Object-Oriented software comprises a process pattern..

Access modifiers in java

· Visible to the package. the default. No modifiers are needed.

· Visible to the class only (private).

· Visible to the world (public).

· Visible to the package and all subclasses (protected).

Class and interfaces cannot be private.

Using the private modifier is the main way that an object encapsulates itself and hide data from the outside world.

The main() method of an application has to be public. Otherwise, it could not be called by a Java interpreter (such as java) to run the class.

The protected access modifier cannot be applied to class and interfaces. Methods, fields can be declared protected, however methods and fields in a interface cannot be declared protected.

interview-qn2

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