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Core java - Interview Questions and Answers for 'Jp morgan' - 11 question(s) found - Order By Newest

Advanced level question. Frequently asked in High end product companies. Frequently asked in Cognizant and Deloitte ( Based on 2 feedback )
  Q1. Why is String immutable in Java ?Core Java
Anonymous
Ans. 1. String Pool - When a string is created and if it exists in the pool, the reference of the existing string will be returned instead of creating a new object. If string is not immutable, changing the string with one reference will lead to the wrong value for the other references.

Example -

String str1 = "String1";
String str2 = "String1"; // It doesn't create a new String and rather reuses the string literal from pool

// Now both str1 and str2 pointing to same string object in pool, changing str1 will change it for str2 too

2. To Cache its Hashcode - If string is not immutable, One can change its hashcode and hence it's not fit to be cached.

3. Security - String is widely used as parameter for many java classes, e.g. network connection, opening files, etc. Making it mutable might possess threats due to interception by the other code segment.

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   Like         Discuss         Correct / Improve     java   oops   string   string class   immutable  immutability   advanced     Asked in 37 Companies      expert        frequent

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Frequently asked to fresh graduates and less experienced developers. Among the first few questions in many interviews.
  Q2. What are the difference between composition and inheritance in Java?Core Java
Admin
info@buggybread.com
Ans. Composition - has-a relationship between objects.
Inheritance - is-a relationship between classes.

Composition - Composing object holds a reference to composed objects and hence relationship is loosely bound.
Inheritance - Derived object carries the base class definition in itself and hence its tightly bound.

Composition - Used in Dependency Injection
Inheritance - Used in Runtime Polymorphism

Composition - Single class objects can be composed within multiple classes.
Inheritance - Single class can only inherit 1 Class.

Composition - Its the relationship between objects.
Inheritance - Its the relationship between classes.

  Sample Code for inheritance

  Sample Code for composition

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   Like         Discuss         Correct / Improve     java   java concepts   inheritance  object oriented programming (oops)  oops concepts   composition  object oriented programming (oops)  oops concepts   inheritance  object oriented programming (oops)  oops concepts vs composition  object oriented programming (oops)  oops concepts     Asked in 28 Companies      basic        frequent

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  Q3. What is a Lambda Expression ? What's its use ?Core Java
Admin
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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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   Like         Discuss         Correct / Improve     java   java8   lambda expression   architecture     Asked in 57 Companies      expert        frequent

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Advanced level question usually asked in High end product companies. Have been asked in Google and Amazon (Based on 1 Feedback)
  Q4. Describe, in general, how java's garbage collector works ?Core Java
Anonymous
Ans. The Java runtime environment deletes objects when it determines that they are no longer being used. This process is known as garbage collection. The Java runtime environment supports a garbage collector that periodically frees the memory used by objects that are no longer needed. The Java garbage collector is a mark-sweep garbage collector that scans Java dynamic memory areas for objects, marking those that are referenced. After all possible paths to objects are investigated, those objects that are not marked (i.e. are not referenced) are known to be garbage and are collected.

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   Like         Discuss         Correct / Improve     java   garbage collection   java memory management   advanced     Asked in 21 Companies      intermediate        frequent

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  Q5. Does Java support Multiple Inheritance ?Core Java
Anonymous
Ans. Java doesn't support multiple inheritance. Interfaces does't facilitate inheritance and hence implementation of multiple interfaces doesn't make multiple inheritance.

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   Like         Discuss         Correct / Improve     java   oop   oop concepts   inheritence   multiple inheritence   basic interview question     Asked in 8 Companies      basic        frequent

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Very frequently asked. Usually asked with questions related to String.
  Q6. What is an Immutable Object ?Core Java
Anonymous
Ans. Object that can't be changed after instantiation.

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   Like         Discuss         Correct / Improve     java   oops   immutable  immutability     Asked in 27 Companies      basic        frequent

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 Q7. What is PermGen or Permanent Generation ?Core Java
Admin
info@buggybread.com
Ans. The memory pool containing all the reflective data of the java virtual machine itself, such as class and method objects. With Java VMs that use class data sharing, this generation is divided into read-only and read-write areas. The Permanent generation contains metadata required by the JVM to describe the classes and methods used in the application. The permanent generation is populated by the JVM at runtime based on classes in use by the application. In addition, Java SE library classes and methods may be stored here.

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   Like         Discuss         Correct / Improve     java   jvm   memory management   permgen   permanent generation   advanced   architecture     Asked in 9 Companies      expert


Frequently asked at HCL Technologies ( Based on 3 feedback )
  Q8. Difference between Checked and Unchecked exceptions ?Core Java
Anonymous
Ans. Checked exceptions are the exceptions for which compiler throws an errors if they are not checked whereas unchecked exceptions are caught during run time only and hence can't be checked.

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   Like         Discuss         Correct / Improve     java   exceptions   checked exceptions   unchecked exceptions   exception handling   basic interview question     Asked in 37 Companies      basic        frequent

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 Q9. Give an Example of checked and unchecked exception ?Core Java
Anonymous
Ans. ClassNotFoundException is checked exception whereas NoClassDefFoundError is a unchecked exception.

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   Like         Discuss         Correct / Improve     java   exceptions   checked exceptions   unchecked exceptions   exception handling     Asked in 2 Companies


  Q10. Write a Program to check if 2 strings are Anagrams ?Core Java2016-11-30 20:52:37

Ans. public void checkIfAnagram(String str1,String str2){
boolean anagram = true;
for(char c:str1.toCharArray()){
if(!str2.contains(String.valueOf(c))){
System.out.println("Strings are Anagrams");
anagram = false;
}

if(anagram == true){
System.out.println("Strings are not Anagrams");
}
}
}

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   Like         Discuss         Correct / Improve      check if 2 strings are Anagrams     Asked in 30 Companies      basic        frequent


Very frequently asked.
 Q11. What is the use of synchronized keyword ?Core Java2016-11-04 08:15:53

Ans. Synchronize is used to achieve mutual exclusion i.e at one time, the segment of the code, method that has been declared synchronized should be executed by single thread only and hence the lock needs to be retrieved before executing the segment and then released.

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   Like         Discuss         Correct / Improve     threads  multithreading  synchronized     Asked in 5 Companies      basic        frequent




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