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Q1861. why is "".equals(str); safer than str.equals("")?

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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Q1862. What is the minimum number of tables required to perform a SQL join?

Ans. 1 , We can do self join

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Q1863. How would you test a Twitter application ?

^{This question was recently asked at 'Slalom'.This question is still unanswered. Can you please provide an answer.}

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Q1864. Can we keep application configuration at different places and what could be the consideration for choosing multiple places for doing so ?

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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Q1865. Do you think it's a good practice to keep passwords in config files ?

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

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Q1866. How to write an iterator for an iterator of iterators?

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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Q1867. What are the disadvantages of binary search trees?

^{This question was recently asked at 'ServiceNow'.This question is still unanswered. Can you please provide an answer.}

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Q1868. Please explain the architecture of our application through a diagram ?

^{This question was recently asked at 'Alfresco Software,Ancestry'.This question is still unanswered. Can you please provide an answer.}

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Q1869. How many heaps will be there with 3 threads ?

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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Q1870. What does 'variable hoisting' mean?

Ans.

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Q1871. Explain when you would decide to use open 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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Q1872. Why Hadoop serialized data types are not using in Spark serialization ?

^{This question was recently asked at 'Tavant Technology'.This question is still unanswered. Can you please provide an answer.}

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Q1873. Explain CloneNotSupportedException ?

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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Q1874. Does abstract class have public constructor?

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

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Q1875. Can we use Param Store with AWS Lambda ?

Amazon Web Services (AWS)

Ans. Yes

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Q1876. Difference between equals and compareTo in 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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Q1877. Difference between equals and hashcode in 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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Q1878. 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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Q1879. Why is String a class in Java ?

Ans. 1. Creating a class helps in specifying operations on the Strings like length , sub string , concatenation etc.

2. It acts as a Wrapper class for "Array of Characters" and hence facilitates it's usage in collections, assignment to null.

3. Immutability of String objects facilitates in reuse , security and caching.

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Q1880. difference between ArrayList and array ?

Ans. ArrayList is a variable length collection class whereas arrays are fixed length primitive structure.

We can use generics with arraylist but not with arrays.

We can store primitive data types within arrays but can't with ArrayList. In ArrayList that needs to be converted to Wrapper objects.

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Q1881. Difference between ArrayList and HashSet ?

Ans. ArrayList is a list , i.e an implementation of List interface whereas HashSet is a Set and an implementation of Set interface.

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Q1882. Difference between HashMap and Dictionary in Java ?

Ans. HashMap implements the Map interface while the Dictionary does not.

HashMap was introduced after HashTable and Dictionary.

Dictionary is currently obsolete in java.

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Q1883. Difference between System.getEnv and System.getProperties ?

Ans. System.getEnv gets the environment variables where System.getProperties gets Java properties.

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Q1884. Can we load environment variables into Properties in Java ? How ?

Ans. Yes

new Properties().putAll(System.getenv());

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Q1885. Sort an Employee Object based on Name or Age

Ans. Use Comparable or Comparator interface

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Q1886. What is cluster ?

^{This question was recently asked at 'idealake information technologies'.This question is still unanswered. Can you please provide an answer.}

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Q1887. What is the concept of hibernate versioning ?

^{This question was recently asked at 'Tata Consultancy (TCS)'.This question is still unanswered. Can you please provide an answer.}

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Q1888. If we have a return statement inside the finally block, Then what will happen ?

Ans. Returning from inside a finally block will cause exceptions to be lost. A return statement inside a finally block will cause any exception that might be thrown in the try block to be discarded.

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Q1889. Can we have more than two constructors in a class ?

Ans. Yes, through constructor overloading

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Q1890. What are the limitations of Java ?

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