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Q1741. Can we send payload / body with the GET Request in Rest ?

Ans. We can send it but it's completely ignored by the server.

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Q1742. Is it Necessary to send a POST request with the Payload or a body ?

Web Service

Ans. No, we can also send an empty body with the POST Request.

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Q1743. Should a DB Insert Request be a POST or PUT request in Rest

Rest

Ans. It depends on whether the request object is persisted as it is

or

its first dismantled, modified or refactored and then inserted into DB.

In first case, it should be a PUT request whereas in second case it should be a POST Request.

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Q1744. Should a Database Update Request be a POST or PUT Request in Rest

Rest

Ans. It should be a POST Request

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Frequently asked question in companies using Rest Web services.

Q1745. Different between POST and PUT in Rest

Rest

Ans. PUT requests are only meant to place the object as it is on server. For example - You want a file to be uploaded and then placed in a particular folder or you want an Employee object to be persisted in the table.

POST requests are also meant to transfer information from client to server but that information once received at the server is evaluated , modified or refactored before persisting.

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Q1746. Why do we use a copy constructor ?

Ans. Copy Constructor is used for creating a duplicate of another object. Duplicate object will have the same state of the copied object but will have independent values in different memory locations. Copy Constructor can be useful to create duplicates of immutable objects as the Original cannot be tampered. Moreover It can be useful if base copies are required for individual requests in threading.

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Q1747. What is a publisher in Jenkins ?

Jenkins

Ans. A publisher is part of build process that reports whether the build is stable or not. For example - Junit Test report publisher.

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Q1748. Does default methods introduce multiple inheritance and the Diamond problem in Java 8 ?

Core Java

Ans. Default methods results in multiple inheritance of behavior and not of state. In case we try to implement multiple interfaces with default method having same name and signature, and don't override it in implementation class, it will throw an error.

For example -

interface MyInterface {
public void default myMethod(){
}
}

interface MyInterface2 {
public void default myMethod(){
}
}

class MyClass implements MyInterface,MyInterface2 {
}

This code will compilation error "Duplicate Default Method"

if we specify the definition of myMethod() in myClass, compiler won't complain and there is no conflict and MyClass can use overridden definition. But if we don't override myMethod() in MyClass, Java would be in conflict as to what definition should be carried to MyClass and hence throws compilation error.

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Q1749. Do all java classes need a main method?

Ans. No, Main method is the entry point into an application. An application usually contain multiple classes to perform a function.

Lets take an example of a House, House usually have only one external Door and you may have internal doors to move around within a house. Internal Doors are methods of classes whereas External Door is a special method called main method.

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Q1750. What are the different uses of Interfaces in Java ?

Core Java

Ans. 1. Regulation / Enforcement / Policy / Contract , It's primary use

2. Use as a collection of utility methods(since java 8 through default methods)

3. Collecting constants together, As Interface are lighter, it makes sense to use them instead of classes if no getters and setters required.

4. Creation of Custom Annotations

5. Special services like marker interface

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Q1751. What are Node / Slaves in Jenkins ?

Jenkins

Ans. Slaves are computers that are set up to build projects for a master.

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Q1752. What is a stable build ?

Jenkins

Ans. A build is considered stable if it was built successfully and no publisher reports it as unstable.

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Q1753. What is the upstream and downstream project in Build Systems ?

Jenkins

Ans. Upstream project is a project whose successful build is required for executing the existing project build whereas Downstream project is the one that is waiting for the upstream project to build as it has the upstream project as dependency.

For example - X project has an upstream project y and downstream project Z. So It means X has dependency Y and is a dependency for Z.

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Q1754. What is the difference between broken and unstable build ?

Jenkins

Ans. Broken Build means as unsuccessful build whereas unstable build means build was created successfully but one of the Post Build report failed or could be a Test failure.

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Q1755. Is this code legal in Java ?

public class BuggyBread {
{
System.out.println("HelloWorld.");
}
}

Ans. Yes, It's an instance initialization block.

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Q1756. What is the difference between constructor and instance initialization blocks ?

Core Java

Ans. Constructor has the same name as class name whereas instance initialization block just have a body without any name or visibility type.

instance initialization blocks are useful if we want to have some code run regardless of which constructor is used or if we want to do some instance initialization for anonymous classes.

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Q1757. What is "Instance Initializer block" ?

Ans. Instance Initializer block is used to initialize the instance data member. It run each time when object of the class is created.

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Q1758. What is a static variable in Java ?

Core Java

Ans. It is a class level variable that is shared among the objects of that class.

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Q1759. What is the difference between print() and println() in Java ?

Ans. print method prints the argument passed to the method whereas println prints the argument and then prints the new line character. println is generally used if we want each output in a new line.

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Q1760. Can I run a java program without creating any class ?

Ans. No, It requires creation of atleast one Class. Creating an object of that class is not compulsory as we can write all our logic within main method which is static.

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Q1761. What was the driving force to introduce default methods in Interfaces wef from Java 8 ?

Core Java

Ans. Earlier any class implementing an interface was supposed to implement all methods declared in an interface. There was no place for optionally implementing all or subset of methods.Though we have abstract classes wherein we could have provided such a mechanism by declaring some methods as abstract while providing definition for some. But as Abstract classes have a body and are comparatively heavier than interfaces and interfaces associate closely to the concept of providing interfacing than abstract classes, Java might have though of providing optional implementation for default methods. This way same interface can be reused in variety of ways rather than making copies of an interface to suit different needs.

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Q1762. What is the purpose of Commit and Rollback in Databases ?

Database

Ans. When a DML is executed, the changes only stays in session and still not pushed to DB Tables, Commit is used to push those changes to the Tables.

In case we realize that we don't want to commit those changes and would like to ignore them, we can use rollback.

For example - You may like that for a banking transaction you would like to update the account balance only if the debit or credit record was correctly inserted, so you may like to encapsulate both DML's - insert for transaction and update for balance in a single transaction and would only commit if both succeeds else rollback.

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Q1763. What are some alternates to keeping Audit Tables ?

Database

Ans. Audit Tables generally stores Raw information to be reviewed in case of problems or determining impact. If Database space is an issue , and the audit information is rarely retrieved, one design could be to use compressed file system.

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Frequently asked for Lead and Architect positions. Recently asked in many US companies.

Q1764. What are Anti Patterns ?

Design

Ans. Anti-pattern is simply the creation of a pattern in your coding that negatively affects your code i.e the Negatives surpasses the positives.

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Q1765. When do we generally get the database error - Unique Constraint Violated ?

Ans. This error can result either on an insert, update or delete when any change in data results in duplicate record or subset of it having unique constraint on record or its subset. For example - If we have a unique constraint on a combination of columns and then trying to insert duplicate column values.

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Q1766. When do we generally get this database error - integrity constraint violated - parent key not found ?

Ans. This error most likely will be thrown during an insert statement, while inserting a value within a foreign key column which doesnt exist within the Parent column. For example - Trying to add a dept number reference within a Employee Table when the Dept doesnt exist in the Dept Table.

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Q1767. Why HashTable has been deprecated ?

Core Java

Ans. HashTable has been deprecated. As an alternative, ConcurrentHashMap has been provided. It uses multiple buckets to store data and hence much better performance than HashTable. Moreover, there is already a raw type HashMap. The only difference between the HashTable and HashMap is that Hashtable is synchronized whereas HashMap is not. Most of the synchronized collections have been deprecated and their raw alternative have been presented as preferred.Synchronization has a cost. Using synchronized collection in places where there is no need of it leads to useless utilization of resources. As these collections are rarely used in a static context or shared among threads, Java might have thought it better to just provide the raw collection and let developers implement synchronization if he feels the need to do so. HashMap is now presented as the default and the preferred way of using Map with read optimized hashing, and ConcurrentHashMap has been provided for synchronized access which provides better performance than HashTable. Because of this, Java thought it right to deprecate the use of HashTable.'

Synchronization has a cost. Using synchronized collection at a place where there is hardly any need of it would means useless utilization of resources. As these collections are rarely used in static context or shared among threads, Java might have thought it better to just provide the raw collection and let developer implement synchronization if he feels the need to do so.

As HashMap has been presented as default and preferred way of using Map with read optimized hashing, and ConcurrentHashMap has been provided for synchronized access which provides better performance than HashTable, Java thought it right to deprecate the use of HashTable.

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Q1768. What is a self Join and give an example of a self Join ?

or

What is self Join and What is it's purpose ?

Database

Ans. When a Table Join itself , it's a Self Join. For example - we like to know the pair of department names where first dept has lesser employees than the later.

Select D1.name , D2.name from Dept D1, Dept D2 where D1.employee_count < D2.employee_count

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Q1769. What is the difference between the following two code lines ?

1. new OuterClass().new InnerClass();

2. new OuterClass.InnerClass();

Core Java

Ans. In first case we are trying to initialize Inner class object using the instance of Outer Class whereas in second case we are trying to initialize the Inner class object directly using the Outer class name.

In second case , Inner class is "static inner class" as we cannot access "non static inner class" using Classname alone.

In first case, the inner class could be either "static inner class" or "non static inner class".

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Q1770. What is multilevel inheritance ?

Core Java

Ans. Multi Level Inheritance is multi level hierarchy of classes. Here is the example - http://www.buggybread.com/2015/09/java-se-class-diagram-classes-that_603.html

Class RoleList extends ArrayList which in turn extends AbstractList which in turn extends AbstractCollection.

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