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Core java - Interview Questions and Answers for 'Ebay' - 19 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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Very frequently asked in different variations. Frequently asked in Deloitte ( 2 feedback ) , HCL Tech ( 3 feedback ) and Coginizant (CTS)
  Q2. Explain the scenerios to choose between String , StringBuilder and StringBuffer ?

or

What is the difference between String , StringBuilder and StringBuffer ?
Core Java
Anonymous
Ans. If the Object value will not change, use String Class because a String object is immutable.

If the Object value can change and will only be modified from a single thread, use StringBuilder because StringBuilder is unsynchronized(means faster).

If the Object value may change, and can be modified by multiple threads, use a StringBuffer because StringBuffer is thread safe(synchronized).

  Sample Code for String

  Sample Code for StringBuffer

  Sample Code for StringBuilder

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Frequently asked in Infosys and HCL Technologies ( Based on 2 feedback )
 Q3. What are different ways of object creation in Java ?Core Java
Admin
info@buggybread.com
Ans. Using new operator - new xyzClass()

Using factory methods - xyzFactory.getInstance( )

Using newInstance( ) method - (Class.forName(xyzClass))emp.newInstance( )

By cloning an already available object - (xyzClass)obj1.clone( )

  Sample Code for object initialization using clone

  Sample Code for object initialization using getInstance

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Frequently asked.
 Q4. If you are given a choice to use either ArrayList and LinkedList, Which one would you use and Why ?Core Java
Admin
info@buggybread.com
Ans. ArrayList are implemented in memory as arrays and hence allows fast retrieval through indices but are costly if new elements are to be inserted in between other elements. LinkedList allows for constant-time insertions or removals using iterators, but only sequential access of elements

1. Retrieval - If Elements are to be retrieved sequentially only, Linked List is preferred.

2. Insertion - If new Elements are to be inserted in between other elements , Linked List is preferred.

3. Search - Binary Search and other optimized way of searching is not possible on Linked List.

4. Sorting - Initial sorting could be pain but lateral addition of elements in a sorted list is good with linked list.

5. Adding Elements - If sufficiently large elements needs to be added very frequently ,Linked List is preferable as elements don't need consecutive memory location.

  Sample Code for ArrayList

  Sample Code for LinkedList

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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies. Frequently asked in HCL Technologies, TCS and Accenture.
  Q5. What is the difference between final, finally and finalize() ?Core Java
Admin
info@buggybread.com
Ans. final - constant variable, objects cannot be de-referenced, restricting method overriding, restricting class sub classing.

finally - handles exception. The finally block is optional and provides a mechanism to clean up regardless of what happens within the try block. Use the finally block to close files or to release other system resources like database connections, statements etc.

finalize() - method helps in garbage collection. A method that is invoked before an object is discarded by the garbage collector, allowing it to clean up its state.

  Sample Code for final

  Sample Code for finally

  Sample Code for finalize

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Very frequently asked. Favorite question in Walk in Drive of many Indian service companies.
  Q6. What is the difference between ArrayList and LinkedList ?Core Java
admin
info@buggybread.com
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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Very frequently asked across all types of companies.
  Q7. Difference between HashMap and Hashtable?Core Java
Anonymous
Ans. Hashtable is synchronized whereas HashMap is not.HashMap allows null values whereas Hashtable doesnt allow null values.

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 Q8. Describe what happens when an object is created in Java ?Core Java
Anonymous
Ans. 1. Memory is allocated from heap to hold all instance variables and implementation-specific data of the object and its superclasses. Implemenation-specific data includes pointers to class and method data.
2. The instance variables of the objects are initialized to their default values.
3. The constructor for the most derived class is invoked. The first thing a constructor does is call the constructor for its superclasses. This process continues until the constructor for java.lang.Object is called,as java.lang.Object is the base class for all objects in java.
4. Before the body of the constructor is executed, all instance variable initializers and initialization blocks are executed. Then the body of the constructor is executed. Thus, the constructor for the base class completes first and constructor for the most derived class completes last.

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 Q9. Difference between Static and Singleton Class ?Core Java2016-11-30 21:00:43

Ans. 1. Static class is a class which cannot be instantiated and all its members are static whereas Singleton is the class that only permit creation of single object and then the object is reused.

2. As there is no object in Static class, it cannot participate in runtime Polymorphism.

3. As Static class doesnt allow creating objects and hence it cannot be serialized.

4. Static class body is initialized eagerly at application load time whereas Singleton object can be initiated eagerly using static blocks or lazily on first need.

5. Its not recommended to use pure static class as it fails to use many OOPs concepts.

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Frequently asked in Tech Mahindra ( Based on 3 inputs )
  Q10. What is the difference between List, Set and Map ?Core Java
Anonymous
Ans. List - Members are stored in sequence in memory and can be accessed through index.
Set - There is no relevance of sequence and index. Sets doesn't contain duplicates whereas multiset can have duplicates.
Map - Contains Key , Value pairs.

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Very frequently asked. Usually asked in different variants like Diff between StringBuffer , String Builder ; Difference between StringBuilder and String class; Choice between these classes etc.
  Q11. What is the difference between StringBuffer and String class ?Core Java
Anonymous
Ans. A string buffer implements a mutable sequence of characters. A string buffer is like a String, but can be modified. At any point in time it contains some particular sequence of characters, but the length and content of the sequence can be changed through certain method calls.

The String class represents character strings. All string literals in Java programs, such as "abc" are constant and implemented as instances of this class; their values cannot be changed after they are created.

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Very Frequently asked. Usually asked along with String Class related questions.
  Q12. What is an immutable class ?Core Java
Anonymous
Ans. Class using which only immutable (objects that cannot be changed after initialization) objects can be created.

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Very frequently asked. Usually difference between String,StringBuffer and StringBuilder is asked in different variations.
  Q13. Difference between StringBuffer and StringBuilder ?Core Java
Anonymous
Ans. StringBuffer is synchronized whereas StringBuilder is not.

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  Q14. Write a method to check if input String is Palindrome?Core Java
Admin
info@buggybread.com
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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 Q15. How is HashSet maintained in memory by Java ?Core Java
Admin
info@buggybread.com
Ans. HashSet is maintained as HashMap by Java with values of the HashSet as Keys of the HashMap and value of the HashMap as the constant PRESENT.

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 Q16. Difference between Stack and Heap memory ?Core Java
Admin
info@buggybread.com
Ans. Stack memory areas is used to hold method and local variables while objects are always allocated memory in the heap. The heap memory is shared between multiple threads whereas Stack memory isn't.

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 Q17. What is collision in hash collections ?Core Java
Admin
info@buggybread.com
Ans. Collision is the situation when two different elements have the same Hash Code.

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Frequently asked in face to face interviews.
  Q18. Write a program to print fibonacci series.Core Java

Ans. int count = 15;
int[] fibonacci = new int[count];
fibonacci[0] = 0;
fibonacci[1] = 1;
for(int x=2; x < count; x++){
fibonacci[x] = fibonacci[x-1] + fibonacci[x-2];
}

for(int x=0; x< count; x++){
System.out.print(fibonacci[x] + " ");
}

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  Q19. How are values passed in Java ? By value or reference ?Core Java

Ans. Java only provides pass by value.

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