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Ans. The clustered index determines how the data is stored in the rows of a table.The non-clustered index stores the data at a single place and the indexes are stored at another place.
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Ans. The Java collections framework (JCF) is a set of classes and interfaces that implement commonly reusable collection data structures. Although referred to as a framework, it works in a manner of a library. The JCF provides both interfaces that define various collections and classes that implement them.
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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Ans. The Spring Application starts with the main() method. Spring Application has a Main Class where main() method has a static method run() which takes two arguments, one is class type and second is string array.
Spring Application will bootstrap our application, starts auto-configured tomcat web server.When SpringApplication.run() command is invoked, the Application Context is created. The createApplicationContext method checks if it is a web or standalone application based on the type it creates for the context.When the constructor of the context is invoked, it will register the annotated class beans with the context. All your @Repository, @Component, @Service, and Controller beans will be registered and the context is returned.
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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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Ans. Its is the process of creating exact copy of an object being cloned. In Object class one native method called clone() is there which is meant for Shallow Cloning of Object. Shallow cloning means bitwise copy of an object.In case of primitive data type it will create an exact copy of primitive values as well as variables but if the object contains any reference of an object then it will not copy the referenced object rather it will create the copy of reference variable and assigned it to the old object.
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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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Ans. The build path is used for building your application. It contains all of your source files and all Java libraries that are required to compile the application.
The classpath is used for executing the application. This includes all java classes and libraries that are needed to run the java application.
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Ans. JDK(Java Development kit) = Development Kit comprising of JVM , library and development tools for developers
JRE (Java Run time Environment) - Comprise of JVM and set of libraries
JVM(Java Virtual Machine) = Interpreter which reads the .class file line by line.
When we install JDK, JRE also get installed so we can write,compile and excute our code. Used by developer. Without JDK we can only execute the program using JRE.
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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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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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Q956. What is read and write optimization in relation to databases ? Which database facilitates read optimization and which facilitates write optimization ?
Ans. A falsy value is something which evaluates to FALSE, for instance when checking a variable. There are only six falsey values in JavaScript: undefined, null, NaN, 0, "" (empty string), and false of course.
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