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Q451. Difference between equals and equalsignorecase in Java ?

Ans. "equals" method is the method of object class that needs to be overridden to check object equality. This is not specific to any class like String.

equalsignorecase is the method of String class that provides a definition that ignores the case of characters during comparison.

The only difference between them in String class is that the equals() methods considers the case while equalsIgnoreCase() methods ignores the case during comparison.

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Q452. Difference between equals and hashcode in java ?

Core Java

Ans. "equals" is the method of object class which is supposed to be overridden to check object equality. x.equals(y) means the references x and y are holding objects that are equal with the equality defined by the definition of equals method.

Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc. The value received from hashcode() is used as bucket number for storing elements. This bucket number is the address of the element inside the set/map. when you do contains() then it will take the hashcode of the element, then look for the bucket where hashcode points to and if more than 1 element is found in the same bucket (multiple objects can have the same hashcode) then it uses the equals() method to evaluate if object are equal, and then decide if contain() is true or false, or decide if element could be added in the set or not.

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Q453. Difference between equals and compareTo in Java ?

Core Java

Ans. "equals" is the method of object class which is supposed to be overridden to check object equality. x.equals(y) means the references x and y are holding objects that are equal.

The compareTo() method is used for comparing two objects in Java. It is usually defined for the classes whose objects needs to be ordered through Comparable interface or need to be part of an ordered collection like TreeSet or TreeMap.

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Q454. Is ConcurrentHashMap synchronized ?

Core Java

Ans. Yes, ConcurrentHashMap is synchronized.

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Q455. Is HashMap Synchronized ?

Core Java

Ans. No HashMap isn't synchronized. ConcurrentHashMap and Hashtable are synchronized.

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Q456. Can we use Param Store with AWS Lambda ?

Amazon Web Services (AWS)

Ans. Yes

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Q457. What measures would you take to avoid Java threading issues in a multi-threaded environment ?

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Q458. Does abstract class have public constructor?

Core Java

Ans. Yes, an abstract class can have a constructor in Java.

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Q459. Explain CloneNotSupportedException ?

Core Java

Ans. If we do not mention, Cloneable Interface to the Class which we want to Clone then we get this exception, only if we try to clone an object

Like:
public class TestClone{
@Override
   protected Object clone() throws CloneNotSupportedException {
      return super.clone();
   }
}

In Main, You try to do:
TestClone clone = new TestClone();

      TestClone clone2 = (TestClone) clone.clone();

You will get CloneNotSupportedException.

Just add -> public class TestClone implements Cloneable {

and things are fixed.

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Q460. Why Hadoop serialized data types are not using in Spark serialization ?

BigData

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Q461. Explain when you would decide to use open authentication ?

Authentication

Ans. Google OAuth can be used when we want to grant the access of our google credentials to the service provider ( most likely a cloud-based mobile application) by using the option ' Login via Google'

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Q462. What does 'variable hoisting' mean?

JavaScript

Ans.

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Q463. How many heaps will be there with 3 threads ?

Core Java

Ans. All threads share a common heap.

Each thread has a private stack, which it can quickly add and remove items from. This makes stack based memory fast, but if you use too much stack memory, as occurs in infinite recursion, you will get a stack overflow.

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Q464. Please explain the architecture of our application through a diagram ?

General

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Q465. Design a appointment booking system for a chain of hospitals.

Design

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Q466. What are the disadvantages of binary search trees?

Algorithm

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Q467. How does one do matrix multiplication?

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Q468. What is an identity matrix ?

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Q469. How to write an iterator for an iterator of iterators?

Core Java

Ans. CustomArrayList myarrayList = new CustomArrayList();
      myarrayList.add("Value 1");
      myarrayList.add("Value 2");
      myarrayList.add("Value 3");

      for (String string : myarrayList) {
         System.out.println(string);
      }

package sample.utils;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class CustomArrayList implements Iterable {

   private ArrayList mylist = new ArrayList();

   public void add(T t) {
      this.mylist.add(t);
   }

   @Override
   public Iterator iterator() {
      return new CustomIterator(mylist);
   }

   class CustomIterator implements Iterator {

      private int indexPosition = 0;
      private List internalList;

      public CustomIterator(List internalList) {
         this.internalList = internalList;
      }

      @Override
      public boolean hasNext() {
         if (internalList.size() >= indexPosition 1) {
            return true;
         }
         return false;
      }

      @Override
      public E next() {
         E val = internalList.get(indexPosition);
         indexPosition ;
         return val;
      }

   }

}

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Q470. Do you think it's a good practice to keep passwords in config files ?

Solution

Ans. We can keep them in config as encrypted values.

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Q471. Can we keep application configuration at different places and what could be the consideration for choosing multiple places for doing so ?

Design

Ans. Yes an application can have configuration stored at multiple places. Factors that could facilitate such a design could be

1. Type of config information - We may have a case to store confidential information differently than other regular config value

2. Environment - We may like to have a base config ( defined in application package ) and then a different override mechanism in different environments.

3. Centralization - Sometime some configs need to be shared across application and hence centralized.

4. Testing - Testing against config may not be possible in some enviornments in certain cases and hence additional config store might be kept for testing purpose only.

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Q472. Write a calculator and find if a character appears more than n times ?

Design

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Q473. How would you test a Twitter application ?

Testing

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Q474. Implement a queue, using only stacks

Data Structure

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Q475. Code an elevator simulator.

Design

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Q476. What is the minimum number of tables required to perform a SQL join?

Database

Ans. 1 , We can do self join

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Q477. What is a difference between JUnit 3 and 4 ?

Junit

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Q478. Can we have a final argument in a method ? What is the use of that if we do so ?

Core Java

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Q479. why is "".equals(str); safer than str.equals("")?

Core Java

Ans. str.equals("") this statement will throw NullPointerException if str is null where as "".equals(str) works fine even if str is null

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Q480. Write a method that would solve two problems at the same time ?

Core Java

Ans. We can return value for one problem solving or computation and set the value for other in some member element.

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