Interview Questions and Answers for 'L' | Search Interview Question

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Q871. 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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Q872. What is the difference between following two if blocks ?

if(x < 10)
do this;

else if(x > 10)
do that;

else
do this and that;

if(x < 10)
do this;

if(x > 10)
do that;

if(x == 10)
do this and that;

Ans. Though Logically both code segments are same, but first one is more efficient as the 3 checks are mutually exclusive. In second code segment, all conditions will be evaluated no matter what and will never result in short circuit. In first segment , max 2 conditions will be checked if x >= 10.

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

Q873. 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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Q874. 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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Q875. 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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Q876. 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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Q877. 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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Q878. 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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Q879. 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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Q880. 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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Q881. 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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Q882. 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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Q883. 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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Q884. 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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Q885. 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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Q886. 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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Q887. 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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Frequently asked question in companies using Rest Web services.

Q888. 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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Q889. 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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Q890. Can I hit the Rest Post Request through a browser address bar if it's not expecting any payload / body ?

Rest

Ans. No, even if there is no payload, you can't hit the POST request by typing it into browser address bar. You will need a client that can make a POST Request.

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Rarely asked as it was introduced with Java 8.

Q891. What is the use of :: operator wef from Java 8 ?

Core Java

Ans. We can refer to a function using this operator like System.out.println(intList.stream().reduce(Math::max).get());

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Q892. Can we declare the main method as private ?

Core Java

Ans. Yes, compiler won't complain but at runtime it will give an error saying "Error: Main method not found in class". Even though we can use this method as any other private method, it cannot be invocate by executing the class.

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Q893. What is Hot Deployment ?

Server

Ans. It is the ability to deploy changes on the fly without need to first build , deploy and then restart. All these functions happens on the fly as soon as the changes are made to the code.

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Q894. Difference between Hot and Cold Deployment ?

Server

Ans. Cold Deployment is a conventional deployment mechanism that follows the multi step process to deploy code changes to the running app i.e Build -> Deploy - Restart.

whereas

Hot Deployment is deployment changes on the fly without need to first build , deploy and then restart. All these functions happens on the fly as soon as the changes are made to the code.

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Q895. What is wrong with the following if statement ?

if(x==y && x.equals(y) {
}

Core Java

Ans. x==y means that both references have same type and are pointing to same memory location and hence would always mean that they have same value.

x.equals(y) is not required in this case.

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Q896. What is wrong with the following if statement ?

if(x==y || x.equals(y) {
}

Core Java

Ans. if x==y turns out to be true x.equals(y) will be true too. If x.equals(y) could be true even if x==y is true or not.

So the only possible outcomes are

1 || 1 = 1
0 || 1 = 1
0 || 0 = 0

i.e the outcome of x.equals(y)

check for x==y is not required in this if statement.

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Q897. Does it make sense to clone an object which is supposed to be immutable ?

Design

Ans. It make sense only if we intend to modify either of the object and would like to preserve original state in other. Otherwise we can reuse the original object by making it singleton.

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Q898. Does an ArrayList allow elements of different types ? If not, Why the following code works List list1 = new ArrayList<>(); list1.add(1); list1.add("1");

Core Java

Ans. With Java 7 or Later. If you don't declare the list to be of specific type , it treats it as list of objects. int 1 is auto boxed to Integer and "1" is String and hence both are objects.

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Q899. Can we access private members of the parent class ? i.e Are private members of the class visible in the derived class ?

Core Java

Ans. No, If both Parent and Derived are outer classes.

public class Vehicle {
private static String manufacturingDate = "2016";
}

public class Car extends Vehicle{
public static void main(String args[]){
System.out.println(manufacturingDate); // error - The field Vehicle.manufacturingDate is not visible
}
}

Yes, If derived is the inner class of Parent.

public class Vehicle {
private static String manufacturingDate = "2016";
static public class Car extends Vehicle{
public static void main(String args[]){
System.out.println(manufacturingDate); // no problem
}
}
}

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Q900. What is IdentityHashMap ?

Core Java

Ans. IdentityHashMap is a class that implements AbstractMap and provides a data structure with Elements having Key Value pair, just like HashMap. It is similar to HashMap except that it uses reference equality when comparing elements.

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