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Q301. How do you check memory leak in Java?

Ans. You need to capture heap dump when it's in the healthy state. Start your application. Let it take real traffic for 10 minutes. At this point, capture heap dump. Heap Dump is basically the snapshot of your memory. It contains all objects that are residing in the memory, values stored in those objects, inbound

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Q302. what is fail fast and Fail Safe in collections?

Core Java

Ans. Iterators in java are used to iterate over the Collection objects.

Fail-Fast iterators immediately throw ConcurrentModificationException if there is any addition, removal or updation of any element.

Fail-Safe iterators don't throw any exception if a collection is structurally modified while iterating over it. This is because, they operate on the clone of the collection and not on the original collection.

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Q303. How to configure Tomcat to have number of user restrictions?

Server

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Q304. Explain OOps concepts.

Core Java

Ans. There are four main OOP concepts in Java. These are:

Abstraction. Abstraction means using simple things to represent complexity. We all know how to turn the TV on, but we don?t need to know how it works in order to enjoy it. In Java, abstraction means simple things like objects, classes, and variables represent more complex underlying code and data. This is important because it lets avoid repeating the same work multiple times.

Encapsulation. This is the practice of keeping fields within a class private, then providing access to them via public methods. It?s a protective barrier that keeps the data and code safe within the class itself. This way, we can re-use objects like code components or variables without allowing open access to the data system-wide.

Inheritance. This is a special feature of Object Oriented Programming in Java. It lets programmers create new classes that share some of the attributes of existing classes. This lets us build on previous work without reinventing the wheel.

Polymorphism. This Java OOP concept lets programmers use the same word to mean different things in different contexts. One form of polymorphism in Java is method overloading. That?s when different meanings are implied by the code itself. The other form is method overriding. That?s when the different meanings are implied by the values of the supplied variables. See more on this below.

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Q305. What is difference between Spring jdbc template and Hibernate ?

Hibernate

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Q306. What are different types of dependency injections ?

Design

Ans. Setter injection
Constructor injection
Interface injection
Look-up method/method injection

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Q307. Explain what happens when insertion is performed in case of ArrayList and LinkedList.

Data Structure

Ans. Array List works on Array and when we add an element in middle of the list, Array List need to update the index of all subsequent elements. I the capacity is full, it even may need to move the whole list to a new memory location . Linked List works on Double linked list algorithm and all it has to do is to adjust the address of the previous and next elements.

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Q308. How can i split a linked list in two parts in java 8?

Core Java

Ans. This can be done using a Spliterator.

LinkedList list = Arrays.asList("names","numbs","birds","animals");
Spliterator split1 = list.Spliterator();
Spliterator split2 = split1.Spliterator();

Now, the LinkedList is split into split1 and split2.
use split2 first then split1 to check the output.

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Q309. Write an efficient program for printing k largest elements in an array. Elements in array can be in any order.

Data Structure

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Q310. How does relational database facilitates read optimization ?

Database

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Q311. Does relational database facilitate read or write optimization while storing information ?

database

Ans. Usually Relational Databases are optimized for writing. Some exception being usage of indices where indices needs to be updated after insertion and eventually helps with Log(n) reading time.

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Q312. What is read and write optimization in relation to databases ? Which database facilitates read optimization and which facilitates write optimization ?

Database

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Q313. What is abstraction ?

Design

Ans. Abstraction is a process of hiding the implementation details and describing only the functionality to the user.

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Q314. Can you explain software design principles cohesion and coupling with an example?

Design

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Q315. Can you write the code for implementing the one to many (student -> courses) relationship in hibernate?

Hibernate

Ans. @OneToMany(cascade = CascadeType.ALL)
@JoinColumn(name = "student_id")
private Set countries;

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Q316. What is meant by dirty object checking in hibernate ?

Hibernate

Ans. Dirty Checking is one of the features of hibernate. In dirty checking, hibernate automatically detects whether an object is modified (or) not and need to be updated. As long as the object is in persistent state i.e., bound to a particular Session, Hibernate monitors any changes to the objects and executes sql.

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Q317. What is the default data type of state variables in Clonable interface and Serializable interface ?

Core Java

Ans. Cloneable and Serializable are Marker Interfaces, So these are empty interfaces with no variables.

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Q318. Write a program for binary tree ?

Data Structure

Ans. public class BinarySearchTree {
//Represent the node of binary tree
public static class Node {
int data;
Node left;
Node right;
public Node(int data) {
//Assign data to the new node, set left and right children to null

this.data = data;
this.left = null;
this.right = null;
}
}
//Represent the root of binary tree

public Node root;
public BinarySearchTree() {
root = null;
}

//factorial() will calculate the factorial of given number

public int factorial(int num) {
int fact = 1;
if (num == 0) return 1;
else {
while (num > 1) {
fact = fact * num;
num--;
}
return fact;
}
}

//numOfBST() will calculate the total number of possible BST by calculating Catalan Number for given key

public int numOfBST(int key) {
int catalanNumber = factorial(2 * key) / (factorial(key 1) * factorial(key));
return catalanNumber;
}
public static void main(String[] args) {
BinarySearchTree bt = new BinarySearchTree();

//Display total number of possible binary search tree with key 5

System.out.println("Total number of possible Binary Search Trees with given key: "
bt.numOfBST(5));
}
}

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Q319. Suppose we have a string "Java is object oriented language" and we have to reverse every alternate word in string. How would we do that using Java program.

Core Java

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Q320. What are annotations and what are it's advantages ?

Core Java

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Q321. How is LinkedList collection class internally implemented ? Is it a Linked List or Doubly Linked List ?

Core Java

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Q322. Which of the two - Arrays or LinkedList - is a better data structure for implementing Queue ? and Why ?

Data Structure

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Q323. Which immutable classes have you worked with ? Can you name some immutable Collections ? How to make an immutable collection ?

Core Java

Ans. string and wrapper class objects

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Q324. Which Data structure can be used for creating Queue ?

Data Structure

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Q325. Is there any schema in mongo DB ?

MongoDB

Ans. There is schema in mongo-db but the schema need not to be defined before creating collection.

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Q326. How can we ensure thread safety in static method ?

Core Java

Ans. By using synchronized static method or synchronized block

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Q327. In a Tree, find common ancestor of two nodes.

Data Structures

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Q328. Write a SQL to find 2nd Max value in a Table.

Database

Ans. SELECT MIN(FIELD) FROM (SELECT TOP 2 FIELD FROM TABLE ORDER BY FIELD DESC)

or

SELECT MAX(FIELD) FROM TABLE WHERE FIELD NOT IN (SELECT MAX(FIELD) FROM TABLE)

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Q329. Design a Database Schema to store Employee Information with each employee having multiple addresses.

Database

Ans. We can have 2 entities i.e EMPLOYEE and ADDRESS and can have a relationship Table , EMPLOYEE_ADDRESS having one to may relationship between the two.

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Q330. Why can we have a static inner class but not a static Top level class in Java ?

Core Java

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