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

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Q421. Can you give a real life example of synchronization

Core Java

Ans. Intersection with traffic light

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Q422. In the Following code which foo will get called.

foo(Integer i){
}

foo(String s){
}

public static void main(){
passing foo(null);
}

Core Java

Ans. ambiguity error

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Q423. Find different combination of given String and trace the output

Core Java

Ans. private void permutation(String prefix, String sufix)
{
int ln = sufix.length();
if(ln == 0) {
System.out.println(prefix);
} else {
IntStream.range(0, ln).forEach(i->permutation(prefix sufix.charAt(i), sufix.substring(0,i) sufix.substring(i 1, ln)));
}
}

call:permutation("", "abcdef");

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Q424. What is composition ?

Core Java

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Sample Code for composition

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Q425. What is an Interface ?

Core Java

Ans. The interface is a mechanism to achieve abstraction. Interfaces can have abstract methods and variables. It cannot have a method body.

Sample Code for interface

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Q426. What is the purpose of JDP and JDK ?

Core Java

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Q427. What is an applet ?

Java EE

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Q428. What is Jar ?

Core Java

Ans. It is a file format based on the popular ZIP file format and is used for aggregating many files into one.

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Q429. Which collection stores element in insertion order ?

Core Java

Ans. LinkedList maintains the insertion order in collection.

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Q430. What is the difference between Java and J2ee ?

Java EE

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Q431. What is collection framework in Java ?

Core Java

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.

Sample Code for Map

Sample Code for HashMap

Sample Code for Treemap

Sample Code for set

Sample Code for hashset

Sample Code for treeset

Sample Code for list

Sample Code for arraylist

Sample Code for linkedlist

Sample Code for queue

Sample Code for priorityqueue

Sample Code for concurrenthashmap

Sample Code for vector

Sample Code for stack

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Q432. What is Method overloading ?

Core Java

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Q433. Explain JVM architecture.

Core Java

Ans. https://dzone.com/articles/jvm-architecture-explained

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Q434. Create a custom hashmap using synchronization.

Core Java

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Q435. What are different methods to get the permanent gen space of running application?

Core Java

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Q436. How do you check memory leak in Java?

Core 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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Q437. 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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Frequently asked in Genpact.

Q438. What is object cloning ?

Core Java

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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Q439. 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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Q440. how does abstraction help your application ?

Core Java

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Q441. Difference between Class Path and Build Path ?

Core Java

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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Q442. Difference between JVM, JRE and JDK ?

Core Java

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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Q443. Which objects are eligible for garbage collection ?

Core Java

Ans. Objects that have lost their reference i.e. they cannot be accessed/used by the program anymore.

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Q444. 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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Q445. Difference between Scriptlet and JSTL.

Javascript

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Q446. What are falsy attributes in javascript ?

Javascript

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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Q447. What is the default data type of Serialized methods?'

Core Java

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Q448. Why cant we start an identifier with a number in Java?

Core Java

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Q449. Which java features makes java different from other languages ?

Core Java

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Q450. What is mutable in Java ?

Core Java

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