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Q91. What will happen if there are no collections in java ?

Ans. Collections in Java is nothing but a library implementation for data structures and algorithm. If it's not available , we might have to include some other library or provide our own implementation.

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Q92. What are the 7 OSI LAYERS ?

Ans. Layer 7 - Application
Layer 6 - Presentation
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical

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Q93. Does it make sense to mock integration calls during stress / load test ?

Ans. No, its usually not done.

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Q94. Explain Hibernate caching mechanism

Ans. Every fresh session having its own cache memory, Caching is a mechanism for storing the loaded objects into cache memory. The advantage of cache mechanism is, whenever again we want to load the same object from the database then instead of hitting the database once again, it loads from the local cache memory only, so that the no. of round trips between an application and a database server got decreased. It means caching mechanism increases the performance of the application.

In hibernate we have two levels of caching

First Level Cache [ or ] Session Cache
Second Level Cache [ or ] Session Factory Cache [ or ] JVM Level Cache

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Q95. Difference between indexing and partioning

Ans. Creating an index creates a separate table. ... Indexes are used to speed the search of data within tables. Partitions provide segregation of the data at the hdfs level, creating sub-directories for each partition. Partitioning allows the number of files read and amount of data searched in a query to be limited

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Q96. serialization and deserialization of singleton class

Ans. The problem with serialized singleton class is that whenever we deserialize it, it will create a new instance of the class. To overcome this scenario all we need to do is to provide the implementation of readResolve() method.

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Q97. What is the difference between try-catch and @ExceptionHandler in Java/Spring Boot?

Ans. ExceptionHandler is Used to handle at Method level

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Q98. Differences between class not found exception and noclassdef found error ?

Ans. ClassNotFoundException is an exception that occurs when we try to load a class at run time using Class.forName() or loadClass() methods and mentioned classes are not found in the classpath.

NoClassDefFoundError is an error that occurs when a particular class is present at compile time, but was missing at run time.

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Q99. How can we schedule Lambda function to run daily ?

Amazon Web Services (AWS)

Ans. We can schedule that through CloudWatch.

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Q100. Difference between StoreModule.forRoot() and StoreModule.forFeature() ?

Ans. forFeature is used for lazily registering reducers with the module.

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Q101. Isnt the use of HashTable and ConcurrentHashMap the same, i.e providing synchronized map collection ?

Ans. Both provide the thread safety but the actual difference come when talk about performance. CHM gives best performance when no of writer threads are less in number.

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Q102. Which s/w is used for adhar card verification for amount transfer?

Ans. The Aadhaar enabled Payment System or AePS

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Q103. Is java fully platform independent ?

Ans. yes, Java is a class-based and object-oriented programming language. It is a platform-independent language i.e. the compiled code can be run on any java supporting platform. It runs on the logic of “Write once, run anywhere”.

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Q104. Does Java SE has Immutable collections ?

Ans. Yes wef from Java 9

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Q105. Where to use interface and abstract class ?

^{This question was recently asked at 'Exterro,Equator Business Solutions'.This question is still unanswered. Can you please provide an answer.}

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Q106. What are basic functions of OOPS ?

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

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Q107. What is TypeCasting ?

Ans. Assigning a value of one type to a variable of another type is known as Type Casting.

Example :

int x = 10;
byte y = (byte)x;

In Java, type casting is classified into two types, Widening Casting(Implicit) widening-type-conversion and Narrowing Casting (Explicitly done) narrowing-type-conversion.

Widening or Automatic type converion - Automatic Type casting take place when,the two types are compatible and the target type is larger than the source type

Example :

public class Test {
public static void main(String[] args) {
int i = 100;
long l = i; //no explicit type casting required
float f = l;//no explicit type casting required
System.out.println("Int value " i);
System.out.println("Long value " l);
System.out.println("Float value " f);
}
}

Narrowing or Explicit type conversion - When you are assigning a larger type value to a variable of smaller type, then you need to perform explicit type casting.

Example :

public class Test{
public static void main(String[] args) {
double d = 100.04;
long l = (long)d; //explicit type casting required
int i = (int)l;//explicit type casting required
System.out.println("Double value " d);
System.out.println("Long value " l);
System.out.println("Int value " i);
}
}

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Q108. Will this give compile time error ?

Object[] strArray = new String[2];
strArray[0] = 5;

Ans. No. But It will throw ArrayStoreException at runtime.

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Q109. If arrays cannot be resized , Why is this code valid

String[] strArray = new String[2];
strArray = new String[5];

Ans. We are not resizing the first array here but assigning the reference strArray to a new Array with size 5.

So after line 2, We have 2 arrays in memory, one with size 2 and other with size 5 with strArray referring to second array with size 5.

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Q110. Is this code valid

String[] strArray = new String[2];
strArray.length = 5;

Ans. It will give compile time error saying "The final field array.length cannot be assigned"

Arrays once initialized cannot be resized.

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Q111. Is this array initialization correct ? If Yes, What will be the size of array ?

String[] strArray = new String[3]{"Buggy","Bread"};

Ans. No. It will result in error saying "Cannot define dimension expressions when an array initializer is provided"

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Q112. Is this array initialization correct ? If Yes, What will be the size of array ?

String[] strArray = new String[]{"Buggy","Bread"};

Ans. Yes, size of the array will be 2.

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Q113. Is this array declaration correct ? If not , Why ?

String[] strArray = new String[];

Ans. No, We haven't specified the size of array to be initialized.

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Q114. Have you ever worked on migrating AWS services and databases from one account to another ?

Amazon Web Services (AWS)

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Q115. Can we declare an array without assigning the size of an array?

Ans. No, It will throw compile time error saying "must provide either dimension expressions or an array initializer"

Alternatively we can provide array initializer like

String[] strArray = new String[]{"Buggy","Bread"};

which will initialize it to size 2 with values as "Buggy" and "Bread"

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Q116. What is ArrayStoreException ?

Ans. It's an exception that is thrown when we attempt to add value of an incompatible type to an array.

For example -

Object[] strArray = new String[2];
strArray[0] = 5;

In this code, strArray reference of type Object has currently been assigned the String array but at line 2 we are trying to add an integer value.

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Q117. What is the difference between ArrayIndexOutOfBoundException and ArrayStoreException?

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Q118. Why Concurrent Collection Classes are fail-fast in Java ?

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Q119. What are the different ways to avoid multi Threading related problems in Java ?

Ans. Synchronization,
Concurrent classes,
Volatile keyword,
Implementing concurrent Lock interface,
Immutable classes

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Q120. What sets you apart from other developers ?

or

What are the distinguished qualities you have ?

Ans. https://blog.timesunion.com/careers/the-10-most-important-personality-traits-for-career-success/633/

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