Interview Questions and Answers for 'T' | Search Interview Question

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Q1841. Which of the OOP's feature - encapsulation or abstraction - is more important ?

Ans. Encapsulation facilitates security by hiding data and logic whereas Abstraction simplifies organization of data and related logic.

As applications scale, both concepts are required for easy management and maintenance. Encapsulation for security and criss cross communication between objects / modules will make it vulnerable. and Abstraction for better organization that enables better understanding of application code and easy maintainability.

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_{Like Discuss Correct / Improve oops oops features oops concepts}

Q1842. Which of the polymorphism type - static or runtime - is more important ?

Core Java

Ans. Method overloading / static polymorphism compared to method overriding / runtime polymorphism has very limited usage as it just opens up an alternate way of defining a different method with the same name.

Method Overriding on other hand opens up many other features like contracting , interfacing , pluging development and hence development of libraries and frameworks.

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Q1843. Which are the thread safe / synchronized / concurrent classes in java collections ?

Core Java

Ans. Stack
Properties
Vector
BlockingQueue
ConcurrentMap
ConcurrentNavigableMap

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Q1844. What are scrollable ResultSet?

Database

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Q1845. Can you write critical section code for singleton design pattern ?

Design

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Q1846. How to instantiate jsp variable from another jsp?

JSP

Ans. using session attribute.

session.setAttribute("userId",userId);

in first jsp

int userId=session.getAttribute("userId");

in second jsp;

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Q1847. Explain toString method ? Which class contains this method ?

Core Java

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Q1848. What will the following code print and Why

class Class1 {
static{
System.out.println("Wow");
}
public static final int xyz=1;
}

class Class2{
public static void main(String[] args) {
System.out.println(String.valueOf(Class1.xyz));
}
}

Core Java

Ans. 1

Reason being that Class1.xyz is replaced with 1 during pre compilation only and a reference to Class1 is never made.

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Q1849. Design ATM machine application using oops.

Design

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Q1850. What could be the reason for allowing private methods in java 9 ?

Core Java

Ans. Java 8 allowed for method implementation using default methods in interfaces. As those default methods could contain complex logic and might need organizing the logic into multiple methods, they have allowed for private methods.

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Q1851. What are the components of Data Warehousing ?

Database

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Q1852. What is mparticle ?

Mparticle

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Q1853. What is the programming advantage of Immutability ?

Design

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Q1854. What are the disadvantages of immutability ?

Design

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Q1855. What is a weak reference ?

Core Java

Ans. A weak reference is a reference that gets removed on the next garbage collection cycle.

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Q1856. Write a program that count the number of access to a method?

Core Java

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Q1857. Difference between Eager and Lazy loading in hibernate ?

Hibernate

Ans. Lazy Loading is loading of entities on demand when subclass is called, while Eager loading is loading of all the sub entity at the start only.

Eager loading is fast as all sub entities are already present, but its heavy(takes more memory)

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Q1858. Should we have instance variables in the Spring Bean which has been scoped as Singleton ?

Spring

Ans. No, if required we should only have final variables. Bean scoped singleton means that only one instance of the bean will be created and will be shared among different requests and hence instance variables will get shared too.

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Q1859. Create a stack of specific size using arrayList?

Data Structure

Ans. public class StackUsingArrayList {
   public static void main(String[] args) {
      List list = new ArrayList();
      list.add("A");
      list.add("B");
      list.add("C");

      Stack stack = new Stack();

      list.forEach(a -> stack.add(a));
      System.out.println(stack);

   }
}

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Q1860. What are the ways to break singleton pattern ?

Design

Ans. If we don't have double checked locking, it can be broken easily through multi threaded access.

Through Reflection.

If multiple class loaders are loading the class.

If the class is serializable or cloneable.

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_{Like Discuss Correct / Improve singleton Asked in 2 Companies expert}

Q1861. Why the singleton class should never implement Cloneable interface ?

Design

Ans. Because Singleton implementation doesn't restrict it from cloning and hence we can have multiple objects when we actually don't intend it to have multiple objects.

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Q1862. How serialization breaks Singleton pattern ?

Design

Ans. It's not serialization but de serialization that breaks purpose of singleton as new objects can be brought to life using the serialized object.

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_{Like Discuss Correct / Improve singleton}

Q1863. How Reflection can break any design pattern ?

Design

Ans. Using java reflection api, we can tweak into a class and modify it's runtime behavior and hence modify the pattern it might be using.

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Q1864. Can you explain following exception

java.lang.ArithmeticException: Non-terminating decimal expansion; no exact representable decimal result.

Core Java

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Q1865. What are we doing here

list.stream().collect(Collectors.groupingBy(ClassA::getElement1,
Collectors.averagingDouble(ClassA::getelement2)));

Core Java

Ans. We are averaging elements of a collection by element1 grouped by element1

* list is the reference of collection
* element1 is the member element returned by getElement1 method of ClassA
* element2 is the member element returned by getElement2 method of ClassA

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Q1866. What will the following code return

list.stream().collect(Collectors.groupingBy(ClassA::getElement1,
Collectors.averagingDouble(ClassA::getElement2)));

Core Java

Ans. Map<DataType1,DataType2> where DataType1 is the data type of element1 ( returned by getelement1 method ) and DataType2 is the data type of element2 ( returned by getElement2 method )

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Q1867. What is the advantage of BidDecimal over Double ?

Core Java

Ans. BigDecimal provides more precision as compared to double.

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Q1868. What does @VisibleForTesting annotation denotes ?

Testing

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Q1869. What should we do If we need to know the IP of the machine where Lambda function runs ?

Amazon Web Services (AWS)

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Q1870. What are different in memory data structures that are used in No Sql Database ?

NoSql Database

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