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 Frequently asked to fresh graduates and less experienced developers. | ||||
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| Ans. 1. Multithreading provides better interaction with the user by distribution of task 2. Threads in Java appear to run concurrently, so it provides simulation for simultaneous activities.The processor runs each thread for a short time and switches among the threads to simulate sim-ultaneous execution (context-switching) and it make appears that each thread has its own processor.By using this feature, users can make it appear as if multiple tasks are occurring simultaneously when, in fact, each is running for only a brief time before the context is switched to the next thread. 3. We can do other things while waiting for slow I/O operations.In the java.iopackage, the class InputStreamhas a method, read(), that blocks until a byte is read from the stream or until an IOExceptionis thrown. The thread that executes this method cannot do anything elsewhile awaiting the arrival of another byte on the stream. | ||||
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 Discuss Correct / Improve  java threads multi threading concurrency multithreading  Asked in 5 Companies  intermediate  frequent | ||||
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| Ans. They are wrappers to primitive data types. They allow us to access primitives as objects. | ||||
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| Discuss Correct / Improve java data types wrapper classes Asked in 3 Companies basic frequent | ||||
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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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| Discuss Correct / Improve session session management java cookies authentication web application ebay intermediate | ||||
| 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. | ||||
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| 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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| Discuss Correct / Improve java string stringbuffer frequently asked Asked in 18 Companies basic frequent | ||||
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| Ans. The JDBC is a pure Java API used to execute SQL statements. It provides a set of classes and interfaces that can be used by developers to write database applications. The steps needed to execute a SQL query using JDBC: 1. Open a connection to the database. 2. Execute a SQL statement. 3. Process th results. 4. Close the connection to the database. | ||||
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| Discuss Correct / Improve java jdbc db connectivity Asked in 2 Companies basic frequent | ||||
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| Ans. We can make a class immutable by 1. Making all methods and variables as private. 2. Setting variables within constructor. Public Class ImmutableClass{ private int member; ImmutableClass(int var){ member=var; } } and then we can initialize the object of the class as ImmutableClass immutableObject = new ImmutableClass(5); Now all members being private , you cant change the state of the object. | ||||
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| Discuss Correct / Improve java oops immutable immutability immutable immutability class technical lead Asked in 5 Companies intermediate frequent | ||||
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| Ans. Yes.we cannot access them directly but we can access them using object reference.Static methods belong to a class and not objects whereas non static members are tied to an instance. Accessing instance variables without the instance handler would mean an ambiguity regarding which instance the method is referring to and hence its prohibited. | ||||
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| Discuss Correct / Improve java oops static static methods java keywords Asked in 1 Companies | ||||
| Frequently asked to fresh graduates. | ||||
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| Ans. When two threads are waiting each other and cant precede the program is said to be deadlock. | ||||
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| Discuss Correct / Improve java threads multi threading operating system deadlock concurrency Asked in 23 Companies basic frequent | ||||
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| Ans. Java does not support pointers. Java does not support multiple inheritances. Java does not support destructors but rather adds a finalize() method. Finalize methods are invoked by the garbage collector prior to reclaiming the memory occupied by the object, which has the finalize() method. Java does not include structures or unions because the traditional data structures are implemented as an object oriented framework. C++ compiles to machine language , when Java compiles to byte code . In C++ the programmer needs to worry about freeing the allocated memory , where in Java the Garbage Collector takes care of the the unneeded / unused variables. Java is platform independent language but c++ is depends upon operating system. Java uses compiler and interpreter both and in c++ their is only compiler. C++ supports operator overloading whereas Java doesn't. Internet support is built-in Java but not in C++. However c++ has support for socket programming which can be used. Java does not support header file, include library files just like C++ .Java use import to include different Classes and methods. There is no goto statement in Java. There is no scope resolution operator :: in Java. It has . using which we can qualify classes with the namespace they came from. Java is pass by value whereas C++ is both pass by value and pass by reference. Java Enums are objects instead of int values in C++ C++ programs runs as native executable machine code for the target and hence more near to hardware whereas Java program runs in a virtual machine. C++ was designed mainly for systems programming, extending the C programming language whereas Java was created initially to support network computing. C++ allows low-level addressing of data. You can manipulate machine addresses to look at anything you want. Java access is controlled. C++ has several addressing operators . * & -> where Java has only one: the . We can create our own package in Java(set of classes) but not in c and c++. | ||||
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| Discuss Correct / Improve java c++ difference between java and c++ programming concepts programming languages architecture technical architect technical lead Asked in 1 Companies | ||||
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| Ans. Struts 1 actions are singleton. So all threads operates on the single action object and hence makes it thread unsafe. Struts 2 actions are not singleton and a new action object copy is created each time a new action request is made and hence its thread safe. | ||||
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| Discuss Correct / Improve java j2ee mvc frameworks struts struts1 struts2 struts 1 struts 2 architecture | ||||
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| Frequently asked to fresh graduates. | ||||
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| Ans. Runnable - waiting for its turn to be picked for execution by the thread schedular based on thread priorities. Running - The processor is actively executing the thread code. It runs until it becomes blocked, or voluntarily gives up its turn. Waiting: A thread is in a blocked state while it waits for some external processing such as file I/O to finish. Sleeping - Java threads are forcibly put to sleep (suspended) with Thread.sleep. they can resume using Thread.resume method. Blocked on I/O - Will move to runnable after I/O condition like reading bytes of data etc changes. Blocked on synchronization - Will move to Runnable when a lock is acquired. Dead - The thread is finished working. | ||||
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| Ans. A Stream is an abstraction that either produces or consumes information. There are two types of Streams : Byte Streams: Provide a convenient means for handling input and output of bytes. Character Streams: Provide a convenient means for handling input & output of characters. Byte Streams classes: Are defined by using two abstract classes, namely InputStream and OutputStream. Character Streams classes: Are defined by using two abstract classes, namely Reader and Writer. | ||||
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| Discuss Correct / Improve java file io streams byte stream character stream file handling Asked in 3 Companies | ||||
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| Ans. co-variant return type states that return type of overriding method can be subtype of the return type declared in method of superclass. it has been introduced since jdk 1.5 | ||||
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| Discuss Correct / Improve java oops inheritence overriding covariant return type jdk5 advanced Asked in 3 Companies expert | ||||
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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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| Discuss Correct / Improve ail fast fail saf Asked in 9 Companies intermediate | ||||
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| Ans. The Spring Application starts with the main() method. Spring Application has a Main Class where main() method has a static method run() which takes two arguments, one is class type and second is string array. Spring Application will bootstrap our application, starts auto-configured tomcat web server.When SpringApplication.run() command is invoked, the Application Context is created. The createApplicationContext method checks if it is a web or standalone application based on the type it creates for the context.When the constructor of the context is invoked, it will register the annotated class beans with the context. All your @Repository, @Component, @Service, and Controller beans will be registered and the context is returned. | ||||
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| Ans. ConcurrentHashMap is a hashMap that allows concurrent modifications from multiple threads as there can be multiple locks on the same hashmap. | ||||
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| Discuss Correct / Improve java collections hashmap map concurrenthashmap concurrenthashmap concurrency general electric ge Asked in 32 Companies rare | ||||
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| Ans. HBM Files ( Mapping ) DB Connection ( DB Connection String , User Name , Password , Pool Size ) SQL Dialect ( SQL variant to be generated ) Show SQL ( Show / No show SQL on Console ) Auto Commit ( True / False ) | ||||
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| Ans. Predicate represents an anonymous function that accepts one argument and produces a result. Supplier represents an anonymous function that accepts no argument and produces a result. Consumer represents an anonymous function that accepts an argument and produces no result. | ||||
 Sample Code for Predicate Sample Code for Supplier Sample Code for Consumer | ||||
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| Discuss Correct / Improve java java8 predicate consumer supplier lambda expression predicate vs consumer vs supplier expert | ||||
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| Ans. 1. Query Optimization ( Query Rewriting , Prepared Statements ) 2. Restructuring Indexes. 3. DB Caching Tuning ( if using ORM ) 4. Identifying the problems ( if any ) with the ORM Strategy ( If using ORM ) | ||||
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| Discuss Correct / Improve java db database hibernate orm at&t overstock.com performance improvement architecture technical lead architect intermediate | ||||
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| Ans. Thread class holds the definition of start method ( This is the method that starts execution of new thread and then calls run method within the scope of new thread ). Interfaces don't hold any definition and so does runnable. So it makes it necessary the usage of Thread class , whatever implementation you choose. When your class extends the thread class, it carries the definition of start method from parent Thread class onto itself and hence new yourClass.start() helps starting a new thread and then executing run method in that new thread scope. When you implement runnable interface , you are just making it sure to the JVM that you have implemented the required method ( run() ) which the Thread start method will look for upon executing start method. | ||||
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| Discuss Correct / Improve java threads multithreading runnable interface thread class | ||||
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| Ans. List | ||||
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| Discuss Correct / Improve collections java sorting | ||||
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| Ans. Encapsulation | ||||
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| Discuss Correct / Improve java java concepts java features oops concepts oops features access protection information hiding | ||||
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| Ans. Parameters are the variables that the method is expected to receive along with the method call. Arguments are the values which are passed on while calling the methods. | ||||
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| Discuss Correct / Improve parameter argument method function parameter vs argument basic | ||||
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| Ans. There are 2 reasons for it. 1. Usage of Primitive types - Though Java provides classes for the primitive data types but as the usage of primitives is permissible, its considered unpure OOP's language. 2. Usage of Static members - Static members belong to the class and not objects and hence not considered fit for pure OOP's programming. | ||||
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| Ans. Constructors are used for initializing the object state once it is initialized and memory has been reserved for it. Destructor is used to de-allocate memory allocated by objects. There are no destructors in Java. Alternatively, Java provides Automatic garbage collection i.e automatically releasing the un-referenced memory. | ||||
| Sample Code for constructor | ||||
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| Frequently asked. Among first few questions in the J2EE segment of interview. | ||||
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| Ans. Deployment Descriptor which is usually web.xml is used to specify the classes, resources and configuration of the application and how the web server uses them to serve web requests.This file is usually added to WEB-INF folder and contains following * Servlet entries and url mapping * Plugins * Some info regarding authentication / filters * Landing Page * Event Handlers | ||||
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| Ans. HashTable has been deprecated. As an alternative, ConcurrentHashMap has been provided. It uses multiple buckets to store data and hence much better performance than HashTable. Moreover, there is already a raw type HashMap. The only difference between the HashTable and HashMap is that Hashtable is synchronized whereas HashMap is not. Most of the synchronized collections have been deprecated and their raw alternative have been presented as preferred.Synchronization has a cost. Using synchronized collection in places where there is no need of it leads to useless utilization of resources. As these collections are rarely used in a static context or shared among threads, Java might have thought it better to just provide the raw collection and let developers implement synchronization if he feels the need to do so. HashMap is now presented as the default and the preferred way of using Map with read optimized hashing, and ConcurrentHashMap has been provided for synchronized access which provides better performance than HashTable. Because of this, Java thought it right to deprecate the use of HashTable.' Synchronization has a cost. Using synchronized collection at a place where there is hardly any need of it would means useless utilization of resources. As these collections are rarely used in static context or shared among threads, Java might have thought it better to just provide the raw collection and let developer implement synchronization if he feels the need to do so. As HashMap has been presented as default and preferred way of using Map with read optimized hashing, and ConcurrentHashMap has been provided for synchronized access which provides better performance than HashTable, Java thought it right to deprecate the use of HashTable. | ||||
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| Discuss Correct / Improve hashtable synchronized collections Why synchronized collections have been deprecated Why HashTable has been deprecated HashTable vs HashMap expert | ||||
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| Ans. 1. HashSet doesnt maintain its elements in any specific order and is all random whereas TreeSet maintains elements in natural order 9 order defined by the equals method of TreeSet element type ) 2. TreeSet doesnt allow null elements whereas HashMap does. 3. As TreeSet orders elements and is hence insertion is comparatively slower. 4. HashSet performs basic operations like add(), remove(), contains(), size() etc. in a constant size time. A TreeSet performs these operations at the order of log(n) time. 5. HashMap in Java internally backs a HashSet. A NavigableMap backs a TreeSet internally. | ||||
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| Frequently asked Generic Question. | ||||
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| Ans. [Open Ended Answer] Usually answered stating your keen interest in the role offered and challenges and opportunities the role offers. | ||||
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| Ans. Yes, That is possible class A { public static void main(String args[]){ if(System.out.printf("Hello World")==null){} } } | ||||
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Which keyword is used to provide explicit access of a code block to single thread ?
