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Q571. why string pool concept for only String but not for StringBuffer ?

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Q572. What are different ways a user can be authenticated other than username / password ?

Authentication

Ans. IP Authentication
IP Range Authentication
Certificates
Authentication Cards

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Q573. Difference between List and LinkedList ?

Core Java

Ans. A List is an child interface of collection interface in java where as Linked list is and implementation class of List interface which has doubly linked as a underlying data structure

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Q574. How to track immediate parent of the child in selenium using xpath?

Selenium

Ans. Using ./

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Q575. If you are given choice to either load object eagerly or lazily , which one would you use in case of singleton pattern ?

Design

Ans. I would choose Eager as the cost for 1 additional object is too minute for any such consideration.

Eager Loading results in Faster access ( Object available at load time) at the cost of additional space.

Lazy loading results in space saving ( Object available at first use ) at the cost of access speed.

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Q576. Is Google App Engine , IAAS, PAAS or SAAS ?

Google Cloud Platform (GCP)

Ans. It's PAAS ( Platform as a service )

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Q577. Why would a cloud customer use resources in multiple regions and zones ?

Cloud Computing

Ans. 1. Fault Tolerance
2. Better Access by bringing the application closer to the users.

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Q578. Have you ever heard about csrf attacks ?

Security

Ans. Yes, Cross-Site Request Forgery (CSRF) is an attack that forces an end user to execute unwanted actions on a web application in which they're currently authenticated.

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Q579. Do you think a csrf token should only be generated after authentication ?

Security

Ans. No, they should be created before authentication too

https://cheatsheetseries.owasp.org/cheatsheets/Cross-Site_Request_Forgery_Prevention_Cheat_Sheet.html#login-csrf

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Q580. What is concurrent interface ?

Core Java

Ans. ConcurrentMap is an interface and it is a member of the Java Collections Framework. It represents a Map that is capable of handling concurrent access to it without affecting the consistency of entries in a map. ConcurrentMap interface present in java.util.concurrent package.

HashMap operations are not synchronized, while Hashtable provides synchronization. Though Hashtable is thread-safe, it is not very efficient. To solve this issue, the Java Collections Framework introduced ConcurrentMap in Java 1.5.

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Q581. Write a program to print next largest palindrome number?

Core Java

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Q582. What are system integrators in Cloud Computing?

Cloud Computing

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Q583. What is cyclic instantiation ? Have you ever faced any problem due to this ?

OOP

Ans. Cyclic instantiation in OOPs may happen if Class A loading results in Class B Loading , and then Class B Loading results in Class C loading and then Class C has a static reference to Class A and hence results in cyclic instantiation or loading.

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Q584. Why cannot we initialize a final field within the constructor if the initialization is within try block ?

Core Java

Ans. What if the initialization throws an exception. In that case , it will let it move forward without initializing the final field. So it's a way to enforce that either the field is initialized or it fails completely.

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Q585. What is a cookie ?

Java EE

Ans. A cookie is a small piece of text stored on a user's computer by the browser for a specific domain. Commonly used for authentication, storing site preferences, and server session identification.

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Q586. Can we reduce the visibility of the overridden method ?

Core Java

Ans. No

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Q587. What is servlet Chaining ?

Java EE

Ans. Multiple servlets serving the request in chain.

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Q588. Can static method access instance variables ?

Core Java

Ans. Though Static methods cannot access the instance variables directly, They can access them using instance handler.

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Very frequently asked. Usually asked in this format or as difference with interfaces / concrete classes.

Q589. What is an abstract class ?

Core Java

Ans. Abstract class is the class that is not supposed to be instantiated. The purpose of the class to only have extension to the derived class.

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Q590. Which interface does java.util.Hashtable implement?

Core Java

Ans. Java.util.Map

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Frequently asked.

Q591. What is an Iterator?

Core Java

Ans. Iterator is an interface that provides methods to iterate over any Collection.

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Q592. Which interface provides the capability to store objects using a key-value pair?

Core Java

Ans. java.util.map

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Q593. Does java allow overriding static methods ?

Core Java

Ans. No. Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.

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Try 3 Question(s) Test

Q594. Difference between long.Class and Long.TYPE ?

Ans. They both represent the long primitive type. They are exactly the same.

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Q595. Does Java provides default copy constructor ?

Core Java

Ans. No

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Frequently asked to fresh graduates.

Q596. What are the difference between Threads and Processes ?

Operating System

Ans. 1. when an OS wants to start running program it creates new process means a process is a program that is currently executing and every process has at least one thread running within it.
2). A thread is a path of code execution in the program, which has its own local variables, program counter(pointer to current execution being executed) and lifetime.
3. When the JavaVirtual Machine (JavaVM, or just VM) is started by the operating system, a new process is created. Within that process, many threads can be created.
4. Consider an example : when you open Microsoft word in your OS and you check your task manger then you can see this running program as a process. now when you write something in opened word document, then it performs more than one work at same time like it checks for the correct spelling, it formats the word you enter , so within that process ( word) , due to different path execution(thread) all different works are done at same time.
5. Within a process , every thread has independent path of execution but there may be situation where two threads can interfere with each other then concurrency and deadlock come is picture.
6. like two process can communicate ( ex:u open an word document and file explorer and on word document you drag and drop another another file from file explorer), same way two threads can also communicate with each other and communication with two threads is relatively low.
7. Every thread in java is created and controlled by unique object of java.lang.Thread class.
8. prior to jdk 1.5, there were lack in support of asynchronous programming in java, so in that case it was considered that thread makes the runtime environment asynchronous and allow different task to perform concurrently.

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Q597. Why java doesn't support multiple Inheritence ?

Core Java

Ans. class A {
void test() {
System.out.println("test() method");
}
}

class B {
void test() {
System.out.println("test() method");
}
}

Suppose if Java allows multiple inheritance like this,

class C extends A, B {
}

A and B test() methods are inheriting to C class.

So which test() method C class will take? As A & B class test() methods are different , So here we would Facing Ambiguity.

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Usually asked only to fresh graduates.

Q598. Why threads block or enters to waiting state on I/O?

Operating System

Ans. Threads enters to waiting state or block on I/O because other threads can execute while the I/O operations are performed.

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Q599. What are transient variables in java?

Core Java

Ans. Transient variables are variable that cannot be serialized.

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Frequently asked to fresh graduates.

Q600. What is the difference between yield() and sleep()?

Operating System

Ans. When a object invokes yield() it returns to ready state. But when an object invokes sleep() method enters to not ready state.

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