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Interview Questions and Answers for 'Ebay' - 30 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 ) and Epam Systems
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
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).
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.
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.
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.
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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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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Ans. MVC is a Design Pattern that facilititates loose coupling by segregating responsibilities in a Web application
1. Controller receives the requests and handles overall control of the request
2. Model holds majority of the Business logic, and
3. View comprise of the view objects and GUI component
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Ans. REST or Representational State Transfer is a flexible architecture style for creating web services that recommends the following guidelines -
1. http for client server communication,
2. XML / JSON as formatiing language ,
3. Simple URI as address for the services and,
4. stateless communication.
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Ans. Cookie and Session are used to store the user information. Cookie stores user information on client side and Session does it on server side. Primarily, Cookies and Session are used for authentication, user preferences, and carrying information across multiple requests. Session is meant for the same purpose as the cookie does. Session does it on server side and Cookie does it on client side. One more thing that quite differentiates between Cookie and Session. Cookie is used only for storing the textual information. Session can be used to store both textual information and objects.
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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.
Q13. What is the difference between StringBuffer and String class ?
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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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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Ans. A source of possible errors in parallel programming, where one thread can cause an error in another thread by changing some aspect of the state of the program that the second thread is depending on (such as the value of variable).
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Ans. Iterators in java are used to iterate over the Collection objects.
Fail-Fast iterators immediately throw ConcurrentModificationException if there is any addition, removal or updation of any element.
Fail-Safe iterators don't throw any exception if a collection is structurally modified while iterating over it. This is because, they operate on the clone of the collection and not on the original collection.
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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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Ans. When a Table Join itself , it's a Self Join. For example - we like to know the pair of department names where first dept has lesser employees than the later.
Select D1.name , D2.name from Dept D1, Dept D2 where D1.employee_count < D2.employee_count
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LikeDiscussCorrect / Improve  sql  joins  self join  self-join  Pair of employee names with first having lesser salary than later  Pair of department names where first dept has lesser employees than the later Asked in 26 Companiesbasic  frequent
Very frequently asked. Usually followed by questions related to private constructor and synchronized access. Frequently asked in JPMorgan and TCS (Based on 2 feedback)
Ans. WeakHashMap uses weak reference for keys, which means if the key object doesn't have any reference then both key/value mapping will become eligible for garbage collection.
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