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

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Q781. What is meant by "Locality of Reference" or "Cache Locality" ?

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Q782. What is dynamic dispatch in Java ?

Core Java

Ans. Dynamic dispatch in java is also known as runtime polymorphism.It is a process in which a call to an overriden method is resolved at runtime.

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Q783. why aren't arrays better than array list ?

Core Java

Ans. 1. Arrays don't provide any built in support for sorting searching like operation and we need to do it explicitly.

2. It can hold only homogeneous objects,

3. We have to reserve memory as no dynamic expansion allowed.

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Q784. Which are the reserved words in Java ?

Core Java

Ans. All Keywords , modifiers ( public , static , final etc ) as well as non modifier keywords ( for, if,switch etc ) are reserved words in java and hence cannot be used as identifiers. Along with keywords , there are few literals that have predefined meaning and hence cannot be used as identifiers, these are true , false and null.

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Q785. What is widening and narrowing conversion in Java ?

Core Java

Ans. Conversion means that the expression / literal / value of one type getting converted to other type.

Widening conversion is the conversion from Type A to Type B where B requires a wider space than A. For example - int to long, float to double, char to String etc. As the value moves to a wider space, there is no loss of information.

Narrowing conversion is the conversion from Type A to Type B where B requires a narrower space space than A. For example - int to long, float to double, char to String etc.As the value moves to a narrower space, there is a loss of information.

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Q786. What is Boxing conversion ?

Core Java

Ans. Boxing conversion converts expressions of primitive type to corresponding expressions of reference type.

For example

boolean to Boolean
long to Long
double to Double

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Q787. What happens to private variables during inheritance ?

Core Java

Ans. Private variables are not inherited. They are simply ignored and not made part of the derived object body.

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Q788. Can we declare a class private ?

Core Java

Ans. We can declare an inner class as private and hence would be restricting it's access from outside. We cannot make outer class as private.

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Q789. Why can't we declare on outer class as private ?

Core Java

Ans. Making an outer class as private will make it inaccessible from anywhere and would make it useless.

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Q790. How can we hide a class in Java ?

Core Java

Ans. By encapsulating it within another class and declaring it private. In such a case, it will only be accessible through parent class or parent class object.

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Q791. What is the use of final keyword ?

Core Java

Ans. final keyword is a modifier that means differently when applied to variables, methods and classes.

1. Final variable cannot be changed once initialized
2. Final method cannot be overridden
3. Final class cannot be sub classed

Sample Code for final variable

Sample Code for final method

Sample Code for final class

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Q792. How would you explain the statement "Java Programs are collection of objects" ?

Core Java

Ans. Java Programs are collection of objects that communicates with each other to get a task accomplished. To add to those objects, there are common spaces ( static i.e common for objects belonging to a class ) that are used too.

We can visualize objects as departments of an organization in real world. Just like Task gets initiated in one department and then files are moved across different departments to get work done. In a similar fashion, a task is initiated in one object ( having main method ) and then information ( through POJOs / DTOs ) is moved across objects to accomplish a task.

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Q793. Why iterators of an array list are fail fast ?

Core Java

Ans. Because it's access isn't synchronized and hence access / modification by multiple threads may lead to inconsistent state.

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Q794. What problem we could have with ArrayList which aren't possible with Vectors ?

Core Java

Ans. ArrayLists aren't synchronized and hence doesn't allow synchronized access. As multiple threads can access an arraylist in parallel, it may result in an inconsistent state.

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Q795. What is the quickest way to find count of duplicate elements in an arraylist, without using iteration or loops ?

Core Java

Ans. We can copy the elements to a Set and then find the difference of count between ArrayList and Set. As Set don't allow duplicates , they will be removed in the set.

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Q796. Write a method, that compare two numbers and return the bigger one ?

Core Java

Ans. int compare(int a, int b) {
a>b? return a: return b;
}

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Q797. Write a Program for insertion sort.

Core Java

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Very frequently asked. Usually among very first few questions.

Q798. Define encapsulation in Java ?

Core Java

Ans. Encapsulation is a feature of OOP's that binds the data and it's associated methods together as a single unit and facilitate protection and data hiding by providing minimal interface to outside. For example - member variables are declared private and are accessed through public methods. Moreover we have private methods that can only be used internally and hence providing minimal interface to outside class through use of public methods.

Sample Code for encapsulation

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Q799. Can an inner class be subclass of it's parent class ?

Core Java

Ans. Yes that can be done

public class OuterClass {
public class InnerClass extends OuterClass {
}
}

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Q800. Is this code legal in java i.e nested class within interface implementing the parent interface ?

public interface MyInterface {
public class MyClass implements MyInterface {
}
}

Core Java

Ans. Yes that's legal in java

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Q801. What are the different types of loops in Java ?

Core Java

Ans. for, while and do while

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Q802. What is an infinite loop ?

Core Java

Ans. Infinite loop is a programming condition wherein the control goes into an infinite loop because the loop termination condition can never be met. For example -

for(int x=1;x>0;x++){
}

in this loop, with each increment the condition x > 0 will remain true till infinity.

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Q803. Is String a Data type in Java ?

Core Java

Ans. String is not a primitive type in java. Anything defined within double quotes like "abc" is an object of String class.

Sample Code for String

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Q804. Are char,String and Char data types in java ?

Core Java

Ans. char is a primitive data type. String is a class. Char is a wrapper class for primitive char.

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Q805. Can we call a constructor for an object twice ?

Core Java

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Q806. Can we compile and execute a Java class without main method ?

Core Java

Ans. No without main method can not be executed it will throw an error illegal start of type. Main method is the entry point of application.

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Q807. Is JDK required on each machine where a Java application needs to be run ?

Core Java

Ans. No, to run application, machine needs just a JRE (Java Runtime Environment)

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Q808. What is the purpose of re throwing the exception when we can provide the handling at the first catch itself ?

Core Java

Ans. Sometimes the calls move across layers of classes and functions and hence each layer needs to perform some function like cleaning if something goes wrong deep inside.

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Q809. What is the problem we could face if we be very liberal with importing classes even if we are not using them ? For example

import java.util.*;
import java.io.*;

Core Java

Ans. It makes application little heavy as we are importing classes that aren't required.

It creates class name conflicts as similar name classes might be available across different packages. In case of such conflicts, we will have to specify the package name with the class name at the time of it's usage.

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Q810. Which java package is loaded by default and hence doesn't require an explicit import statement ?

Core Java

Ans. java.lang

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