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Interview Questions and Answers for 'Compass' - 25 question(s) found - Order By Newest

Very frequently asked. Among first few questions in almost all interviews. Among Top 5 frequently asked questions. Frequently asked in Indian service companies (HCL,TCS,Infosys,Capgemini etc based on multiple feedback )
  Q1. Difference between == and .equals() ?Core Java
Anonymous
Ans. "equals" is the method of object class which is supposed to be overridden to check object equality, whereas "==" operator evaluate to see if the object handlers on the left and right are pointing to the same object in memory.

x.equals(y) means the references x and y are holding objects that are equal. x==y means that the references x and y have same object.

Sample code:

String x = new String("str");
String y = new String("str");

System.out.println(x == y); // prints false
System.out.println(x.equals(y)); // prints true

  Sample Code for equals

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   Like         Discuss         Correct / Improve     java   string comparison   string   object class   ==    equals   object equality  operator     Asked in 289 Companies      basic        frequent

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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q2. What is the difference between ArrayList and LinkedList ?Core Java
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Ans. Underlying data structure for ArrayList is Array whereas LinkedList is the linked list and hence have following differences -

1. ArrayList needs continuous memory locations and hence need to be moved to a bigger space if new elements are to be added to a filled array which is not required for LinkedList.

2. Removal and Insertion at specific place in ArrayList requires moving all elements and hence leads to O(n) insertions and removal whereas its constant O(1) for LinkedList.

3. Random access using index in ArrayList is faster than LinkedList which requires traversing the complete list through references.

4. Though Linear Search takes Similar Time for both, Binary Search using LinkedList requires creating new Model called Binary Search Tree which is slower but offers constant time insertion and deletion.

5. For a set of integers you want to sort using quicksort, it's probably faster to use an array; for a set of large structures you want to sort using selection sort, a linked list will be faster.

  Sample Code for ArrayList

  Sample Code for LinkedList

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   Like         Discuss         Correct / Improve     collections   java   data structures   arraylist   linkedlist     Asked in 61 Companies      Basic        frequent

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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q3. Difference between TreeMap and HashMap ?Core Java
Anonymous
Ans. They are different the way their elements are stored in memory. TreeMap stores the Keys in order whereas HashMap stores the key value pairs randomly.

  Sample Code for treemap

  Sample Code for hashmap

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   Like         Discuss         Correct / Improve     java   collections   map   treemap   hashmap     Asked in 31 Companies      basic        frequent

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 Q4. Can we override compareTo method for Enumerations ?Core Java
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Ans. No. compareTo method is declared final for the Enumerations and hence cannot be overriden. This has been intentionally done so that one cannot temper with the sorting order on the Enumeration which is the order in which Enum constants are declared.

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   Like         Discuss         Correct / Improve     java   compareto   final methods   enum   enumeration      expert


  Q5. What is the use of Transient Keyword ?Core Java
Anonymous
Ans. It in Java is used to indicate that a field should not be serialized.

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   Like         Discuss         Correct / Improve     java   oops   serialization   transient   java keywords     Asked in 38 Companies      intermediate        frequent

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  Q6. Write a method to check if input String is Palindrome?Core Java
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Ans. private static boolean isPalindrome(String str) {

if (str == null)
return false;

StringBuilder strBuilder = new StringBuilder(str);

strBuilder.reverse();

return strBuilder.toString().equals(str);

}

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   Like         Discuss         Correct / Improve     java   string   stringbuilder   stringbuilder   string class   code   palindrome     Asked in 37 Companies      Basic        frequent


 Q7. What is comparator interface used for ?Core Java
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Ans. The purpose of comparator interface is to compare objects of the same class to identify the sorting order. Sorted Collection Classes ( TreeSet, TreeMap ) have been designed such to look for this method to identify the sorting order, that is why class need to implement Comparator interface to qualify its objects to be part of Sorted Collections.

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   Like         Discuss         Correct / Improve     java   collections   treemap   treeset   comparator     Asked in 2 Companies      Intermediate

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  Q8. Can we overload main method in Java ?Core Java
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Ans. Yes, but the overloaded main methods without single String[] argument doesn't get any special status by the JVM. They are just another methods that needs to be called explicitly.

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   Like         Discuss         Correct / Improve     java   main method   overloading   yes-no     Asked in 6 Companies      intermediate        frequent


 Q9. What is a package and what are its advantages ?Core Java

Ans. Package is a namespace that organizes a set of related classes.

Advantages of Packages

1. Better Organization of classes.
2. Saves from the problem of duplicate names as duplicate class names are allowed across different packages.

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   Like         Discuss         Correct / Improve     package  advantages of packages     Asked in 1 Companies      Basic


Frequently asked in CTS ( Based on 2 feedback )
  Q10. What is the difference between comparable and comparator in java.util pkg?Core Java
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Ans. Comparable interface is used for single sequence sorting i.e.sorting the objects based on single data member where as comparator interface is used to sort the object based on multiple data members.

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   Like         Discuss         Correct / Improve     java   java.util   comparable   comparator   collections     Asked in 23 Companies      basic        frequent


  Q11. What is Comparable Interface?Core Java
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Ans. It is used to sort collections and arrays of objects using the collections.sort() and java.utils. The objects of the class implementing the Comparable interface can be ordered.

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   Like         Discuss         Correct / Improve     java   collections   comparable interface     Asked in 7 Companies      intermediate        frequent

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 Q12. public class a {
   public static void main(String args[]){
      final String s1=""job"";
      final String s2=""seeker"";
      String s3=s1.concat(s2);
      String s4=""jobseeker"";
      System.out.println(s3==s4); // Output 1
      System.out.println(s3.hashCode()==s4.hashCode()); Output 2
   }
}

What will be the Output 1 and Output 2 ?
Core Java
Admin
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Ans. S3 and S4 are pointing to different memory location and hence Output 1 will be false.

Hash code is generated to be used as hash key in some of the collections in Java and is calculated using string characters and its length. As they both are same string literals, and hence their hashcode is same.Output 2 will be true.

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   Like         Discuss         Correct / Improve     java   string   hashcode   hash code   string comparison   string pool

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  Q13. What is the use of HashCode in objects ?Core Java
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Ans. Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc.

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   Like         Discuss         Correct / Improve     java   string   hashcode   hash code   string comparison  hashtable     Asked in 17 Companies      basic        frequent


 Q14. How TreeMap orders the elements if the Key is a String ?
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Ans. As String implements Comparable, It refers to the String compareTo method to identify the order relationship among those elements.

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   Like         Discuss         Correct / Improve     java   collections   comparable interface   treemap   compareto


 Q15. Can we add heterogeneous elements into TreeMap ?
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Ans. No, Sorted collections don't allow addition of heterogeneous elements as they are not comparable.

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   Like         Discuss         Correct / Improve     java   collections   comparable interface   treemap


 Q16. Will it create any problem if We add elements with key as user defined object into the TreeMap ?
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Ans. It won't create any problem if the objects are comparable i.e we have that class implementing Comparable interface.

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   Like         Discuss         Correct / Improve     java   collections   treemap   comparable interface


 Q17. How many elements will be there in TreeSet after the last line and Why ?

TreeSet set = new TreeSet();
set .add(new String("abc"));
set .add(new String("abc"));
Core Java
Admin
info@buggybread.com
Ans. One.

As we haven't specified the type of TreeSet, it being evaluated with the first element insertion. Once it's identified that it's of type String and as no comparator has been defined, the comparison is done using the String compareTo method. String compareTo method compares the elements by the content / value.

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   Like         Discuss         Correct / Improve     java   set   treeset   string   compareto   coding   code


 Q18. If we add Enum constants to a sorted collection ( Treemap , TreeSet ), What will be the order in which they will be maintained ?

a. Sorted Collection wont maintain them in any order.
b. Insertion Order
c. Order in which constants are declared.
d. Natural Sorting Order.
Anonymous
Ans. Order in which constants are declared.

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   Like         Discuss         Correct / Improve     enum   collections   sorted collections   treemap   treeset   compareto   comparable   java


 Q19. Where do we generally use comparable interface ?Core Java2016-08-09 10:02:01

Ans. Implementing Comparable interface means that the elements of the class are comparable i.e the class provides the implementation of compareTo method that would help comparing the elements.

This is usually required if we are planning to sort elements of a collection, If compareTo method is not defined , the sorting class / method could never understand a way to compare its elements in order to sort them.

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   Like         Discuss         Correct / Improve     comparable interface

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 Q20. What will be result of following code and why

Integer int1 = 1;
Integer int2 = 1;
String str1 = new String("str");
String str2 = new String("str");
String str3 = "str";
String str4 = "str";

      
System.out.println(int1 == int2);
System.out.println(str1 == str2);
System.out.println(str3 == str4);
Core Java2017-05-08 10:15:00

Ans. true
false
true

Just like Strings, java maintains an integer constant pool too. So 1 will be maintained in integer constant pool and hence reference int2 will point to same integer in pool.

String pool is only for string literals ( defined by "" ) and not for newly created objects and hence str1 == str2 will return false as they are separate objects in memory.

String pool is used for storing string literals so that they can be reused and str3 and str4 will point to same string literal in string pool.


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   Like         Discuss         Correct / Improve     string pool  integer constant pool  string comparison  integer comparison


 Q21. Which of the following is valid greater than and equal to operator in Java ?

>=
=>
Core Java2017-05-20 16:23:47

Ans. >=

=> will result in error.

=> somewhat looks like lambda operator "->"

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   Like         Discuss         Correct / Improve     operators  >= operator  greater than and equal to operator  comparison operators


 Q22. How to sort objects based on one of the field ?Core Java2018-07-04 16:23:09

Ans. Using comparable and comparator and sorted collections like TreeSet or TreeMap.

or

use stream api from java 8 onwards which internally refers to comparable and comparator through lambda expressions

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   Like         Discuss         Correct / Improve     sort  sorting  comprator  comparable  treeset  treemap  sorting collections     Asked in 1 Companies      Basic        frequent


 Q23. Difference between equals and compareTo in Java ?Core Java2019-02-05 16:38:11

Ans. "equals" is the method of object class which is supposed to be overridden to check object equality. x.equals(y) means the references x and y are holding objects that are equal.

The compareTo() method is used for comparing two objects in Java. It is usually defined for the classes whose objects needs to be ordered through Comparable interface or need to be part of an ordered collection like TreeSet or TreeMap.

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   Like         Discuss         Correct / Improve     equals  compareTo  equals vs compareTo


 Q24. Which method needs to be implemented if a class is implementing comparable interface ?Core Java
a. comp
b. compare
c. compareTo
d. compareEquals

Ans.c. compareTo

 Q25. We cannot override compareTo method for ...Core Java
a. Abstract Class
b. Final Class
c. Enum
d. Interfaces

Ans.c. Enum



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