Interview Questions and Answers - Intermediate Level | Search Interview Question

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Q31. What is ConcurrentModificationException ?

Ans. This is the exception that is thrown when we try to modify the non concurrent collection class while iterating through it.

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Q32. What is the role of JSON.stringify ?

Json

Ans. JSON.stringify() turns an object into a JSON text and stores that JSON text in a string.

So If we stringfy above notation , it will become

{"name":"xyz","gender":"male";"age":30}

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Q33. Can I import same package/class twice? Will the JVM load the package twice at runtime?

Core Java

Ans. One can import the same package or same class multiple times. Neither compiler nor JVM complains wil complain about it. And the JVM will internally load the class only once no matter how many times you import the same class.

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Q34. Can we override static methods ? Why ?

Core Java

Ans. No.

Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.

A static method is not associated with any instance of a class so the concept of overriding for runtime polymorphism using static methods is not applicable.

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Q35. Different types of memory used by JVM ?

Core Java

Ans. Class , Heap , Stack , Register , Native Method Stack.

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Q36. Can we declare an abstract method private ?

Ans. No Abstract methods can only be declared protected or public.

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Q37. What is Externalizable interface?

Core Java

Ans. Externalizable is an interface which contains two methods readExternal and writeExternal. These methods give you a control over the serialization mechanism.

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Q38. Difference between new operator and Class.forName().newInstance() ?

Ans. new operator is used to statically create an instance of object. newInstance() is used to create an object dynamically ( like if the class name needs to be picked from configuration file ). If you know what class needs to be initialized , new is the optimized way of instantiating Class.

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Q39. What are the pre-requisite for the collection to perform Binary Search ?

Ans. 1. Collection should have an index for random access.
2. Collection should have ordered elements.

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Q40. What will be the output of following Code ?

class BuggyBread {
   public static void main(String[] args) {
      String s2 = "I am unique!";
      String s5 = "I am unique!";

      System.out.println(s2 == s5);
   }
}

Core Java

Ans. true, due to String Pool, both will point to a same String object.

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Q41. Does java allow implementation of multiple interfaces having Default methods with Same name and Signature ?

Core Java

Ans. No. Compilation error.

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Q42. Difference between Stack and Heap memory ?

Core Java

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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Recently asked in Capital One.

Q43. What will happen if we call perform(null) ?

public void perform(Object obj) {
System.out.println("Object");
}

public void perform(Integer int) {
System.out.println("Integer");
}

Core Java

Ans. compiler will throws error as ambiguous methods

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Very Frequently asked to Senior Software Engineers or Developers.

Q44. Describe some of the Design Patterns you have used ?

Design

Ans. [Open Ended Answer]

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Q45. What is database Normalization ?

Database

Ans. https://en.wikipedia.org/wiki/Database_normalization

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Q46. When is the situation when finally section won't execute ?

Core Java

Ans. If the process / app is abruptly killed or terminated.

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Q47. How can we ensure thread safety in static method ?

Core Java

Ans. By using synchronized static method or synchronized block

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Q48. Describe structure of a Web application.

architecture

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Q49. Does java allow overriding static methods ?

Core Java

Ans. No. Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.

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Q50. What are transient variables in java?

Core Java

Ans. Transient variables are variable that cannot be serialized.

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Q51. Why Java don't use pointers ?

Ans. Pointers are vulnerable and slight carelessness in their use may result in memory problems and hence Java intrinsically manage their use.

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Q52. What is the difference between System.console.write and System.out.println ?

Ans. System.console() returns null if your application is not run in a terminal (though you can handle this in your application)System.console() provides methods for reading password without echoing charactersSystem.out and System.err use the default platform encoding, while the Console class output methods use the console encoding

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Usually asked only to fresh graduates and less experienced developers.

Q53. What is a daemon thread? Give an Example ?

Ans. These are threads that normally run at a low priority and provide a basic service to a program or programs when activity on a machine is reduced. garbage collector thread is daemon thread.

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Q54. Does every class needs to have one non parameterized constructor ?

Core Java

Ans. No. Every Class only needs to have one constructor - With parameters or without parameters. Compiler provides a default non parameterized constructor if no constructors is defined.

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Q55. Can we use "this" within static method ? Why ?

Core Java

Ans. No. Even though "this" would mean a reference to current object id the method gets called using object reference but "this" would mean an ambiguity if the same static method gets called using Class name.

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Q56. What is Comparable Interface?

Core Java

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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Q57. What is the Locale class?

Ans. The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region

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Q58. How do you check memory leak in Java?

Core Java

Ans. You need to capture heap dump when it's in the healthy state. Start your application. Let it take real traffic for 10 minutes. At this point, capture heap dump. Heap Dump is basically the snapshot of your memory. It contains all objects that are residing in the memory, values stored in those objects, inbound

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Q59. Difference between PATH and CLASSPATH ?

Operating System

Ans. PATH is the variable that holds the directories for the OS to look for executables. CLASSPATH is the variable that holds the directories for JVM to look for .class files ( Byte Code ).

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Very Frequently asked. Favorite question in walkins and telephonic interviews. Usually among first few questions. Asked in different variants. Must know for intermediate and expert professionals.Among Top 10 frequently asked questions.

Q60. What is rule regarding overriding equals and hashCode method ?

Core Java

Ans. A Class must override the hashCode method if its overriding the equals method.

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