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Ans. The Permanent Generation (PermGen) space has completely been removed and is kind of replaced by a new space called Metaspace. The consequences of the PermGen removal is that obviously the PermSize and MaxPermSize JVM arguments are ignored and you will never get a java.lang.OutOfMemoryError: PermGen error. | ||||
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Like Discuss Correct / Improve  java   jvm   memory management   permgen   permanent generation   metaspace   advanced   architecture expert | ||||
Frequently asked in Infosys and HCL Technologies ( Based on 2 feedback ) | ||||
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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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Like Discuss Correct / Improve  java   oops   object creation   new operator   class.forname   cloning   ebay Asked in 9 Companies expert | ||||
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Ans. Yes, We can call garbage collector directly but it doesn't guarantees that the gc will start executing immediately. This gc( ) method appears in both Runtime and System classes of java.lang package. | ||||
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Like Discuss Correct / Improve  java   garbage collection   java memory management   jvm   gc   yes no Asked in 4 Companies expert | ||||
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Advanced level question usually asked to senior developers , leads and architects. | ||||
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Ans. Volatile is an instruction that the variables can be accessed by multiple threads and hence shouldn't be cached. As volatile variables are never cached and hence their retrieval cannot be optimized. | ||||
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Like Discuss Correct / Improve  java   java keywords   volatile   synchronization   compiler optimization   variable caching   architecture Asked in 3 Companies expert | ||||
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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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Like Discuss Correct / Improve  java   oops   inheritence   overriding   covariant return type   jdk5   advanced Asked in 3 Companies expert | ||||
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Ans. At the beginning of an object's life, the Java virtual machine (JVM) allocates memory on the heap to accommodate the object's instance variables. When that memory is first allocated, however, the data it contains is unpredictable. If the memory were used as is, the behavior of the object would also be unpredictable. To guard against such a scenario, Java makes certain that memory is initialized, at least to predictable default values before it is used by any code. | ||||
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Asked multiple times in Capgemini. | ||||
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Ans. String is immutable in java and stored in String pool. Once it's created it stays in the pool until unless garbage collected, so even though we are done with password it's available in memory for longer duration and there is no way to avoid it. It's a security risk because anyone having access to memory dump can find the password as clear text. | ||||
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Like Discuss Correct / Improve  java   string class   string   immutable  immutability   string pool   garbage collection   advanced Asked in 6 Companies Expert | ||||
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Ans. Since String is immutable, its hashcode is cached at the time of creation and it doesnt need to be calculated again. This makes it a great candidate for key in a Map and its processing is fast than other HashMap key objects. This is why String is mostly used Object as HashMap keys. | ||||
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Like Discuss Correct / Improve  java   string class   string   immutable  immutability   hashmap   immutable  immutability   hashcode   hash code   advanced Asked in 2 Companies expert   frequent | ||||
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Ans. intern() method keeps the string in an internal cache that is usually not garbage collected. Moreover provide reference for scp object for corresponding string object present in heap memory. | ||||
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Ans. substring method would build a new String object keeping a reference to the whole char array, to avoid copying it. Hence you can inadvertently keep a reference to a very big character array with just a one character string. | ||||
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Like Discuss Correct / Improve  java   string class   string   substring   memory leaks   jvm   memory management   advanced   architecture   technical architect   technical lead expert | ||||
Frequently asked to experienced developers. Recently asked in many US interviews. | ||||
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Ans. When multiple external resources are trying to access the DB locks and runs into cyclic wait, it may makes the DB unresponsive. Deadlock can be avoided using variety of measures, Few listed below - Can make a queue wherein we can verify and order the request to DB. Less use of cursors as they lock the tables for long time. Keeping the transaction smaller. | ||||
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Like Discuss Correct / Improve  java   database   architecture Asked in 7 Companies expert   frequent | ||||
Frequently asked these days as there are major changes in Java 8. | ||||
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Ans. Lambda Expressions , Interface Default and Static Methods , Method Reference , Parameters Name , Optional , Streams, Concurrency. | ||||
Sample Code for Lambda Sample Code for interface default Sample Code for Optional Sample Code for Streams Sample Code for java.time Sample Code for Predicate Sample Code for Consumer Sample Code for MapMerge | ||||
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Like Discuss Correct / Improve  java   java8   technical lead   technical architect Asked in 14 Companies expert   frequent | ||||
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Ans. With Java 8, We can provide method definitions in the Interfaces that gets carried down the classes implementing that interface in case they are not overridden by the Class. Keyword "default" is used to mark the default method. | ||||
Sample Code for interface default | ||||
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Frequently asked at Manhattan Associates ( Based on 2 feedback ) | ||||
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Ans. Its an anonymous method without any declaration. Lambda Expression are useful to write shorthand Code and hence saves the effort of writing lengthy Code. It promotes Developer productivity, Better Readable and Reliable code. | ||||
Sample Code for lambda | ||||
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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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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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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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Not frequently asked as it was introduced with Java 8. | ||||
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Ans. Final variable means a variable that has been declared final and hence cannot be de referenced after initialization. Effective final means a variable that has not been declared final but haven't been reassigned the value after initialization. First is the regulation that restricts the reassignment and will raise a compilation error if we try to do so. Second is the outcome without the restriction. Effective Final is the eventual treatment of the variable that is required for many features. For eq - Java 8 requires that local variables referenced from a lambda expression must be final or effectively final.It means all local referenced from lambda expressions must be such that their value shouldn't be changed after initialization whether declared final or not. | ||||
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Ans. This collections class has been implemented in such a manner that it can never throw ConcurrentModificationException. As it performs update and write operations by creating a new copy of ArrayList, It's slower compared to ArrayList. | ||||
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Ans. Use Case Diagram, Component Diagram for High level Design and Class Diagram , Sequence Diagram for low level design. | ||||
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Like Discuss Correct / Improve  software system analyst   development lead   project lead   technical lead   technical architect expert   frequent | ||||
Frequently asked in Tata Consultancy (TCS) interview ( Based on 2 Feedback ) | ||||
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Ans. JIRA is written in Java and uses the Pico IOC container,Apache OFBiz entity engine, and WebWork technology stack. For remote procedure calls (RPC), JIRA supports REST, SOAP, and XML RPC. | ||||
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Ans. The sorting algorithm is a modified mergesort. This algorithm offers guaranteed n log(n) performance. | ||||
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Ans. Red Black Tree | ||||
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