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

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Q121. How and Why Strings are interned in Java ?

Ans. String class has a public method intern() that returns a canonical representation for the string object. String class privately maintains a pool of strings, where String literals are automatically interned.

these are automatically interned so as to have efficient String comparison using == operator instead of equals which is usually slower.

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Q122. What is the difference between authentication and authorization ?

Authentication

Ans. Authentication is the process of verifying the identity and credentials of the user to authenticate him into the system.

whereas

Authorization is the process by which access to a segment , method or resource is determined.

Authorization is usually a step next to authentication.

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Usually asked to entry level software developers.

Q123. Write a program to swap two variables without using third

Core Java

Ans. public static void main(String[] args) {
   int num1 = 1;
   int num2 = 2;
   num1 = num1^num2;
   num2 = num1^num2;
   num1 = num1^num2;
   System.out.print("num1 = " + num1 +", num2 = "+num2);
}

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Q124. Who invokes a thread's run method ?

Core Java

Ans. After a thread is started using a call to start method, JVM invokes the thread’s run method when the thread is initially executed.

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Q125. Is exit a keyword in Java ?

Core Java

Ans. No exit is a method to exit execution of a program.

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Q126. Is delete a keyword in Java ?

Core Java

Ans. No, delete is not a keyword in Java. Destruction of objects is taken care by Java Garbage Collection mechanism.

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Q127. How does Java handle integer overflows and underflows?

Core Java

Ans. It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

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Q128. What are the different ways to handle an exception ?

Core Java

Ans. 1. Wrap the desired code in try block followed by a catch / finally to catch the exception

2. Declare the throws clause with exceptions that the code is expected to throw as an indication to the calling method to take care of it.

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Q129. Is there a way to know size of an object in Java ?

Core Java

Ans. No, Java doesn't have a sizeOf operator. In C / C++ , its required to determine how much memory allocation is required which is not the case with Java. Java handles memory allocation and deallocation intrinsically.

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Q130. Can we declare static variables as transient ?

Core Java

Ans. It's weird that compiler doesn't complain if we declare transient with static variable because it makes no sense. At least a warning message saying "transient is useless in this situation" would have helped with code cleaning.

Static variables are never serialized and transient is an indication that the specified variable shouldn't be serialized so its kind of double enforcement not to serialize.

It could be that as it makes no different to the variable behavior and hence using both keywords with a variable are permitted.

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Q131. Which elements of a class are ignored during serialization ?

Core Java

Ans. 1. Objects are serialized and not classes and hence Static variables are ignored.

2. Transient is an explicit declaration to ignore the variable during serialization and hence transient instance variables are ignored too.

3. Base class instance variables if the base class hasn't been declared serializable.

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Q132. What is the default value of a declared object reference ?

Core Java

Ans. Null

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Q133. Is it a good practice to use Asterick(*) in import statement to load multiple packages with single import statement ?

Core Java

Ans. No, we should be lean in loading only packages which are required. Loading packages which are not being used result in memory overheads.

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Q134. Does importing a package imports all its sub packages too ?

Core Java

Ans. No, but we can use wild card (*) to do so

For example -

import java.util.*

will import all packages with name starting with java.util

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Q135. Can we have multiple main methods in a single class ?

Core Java

Ans. We can overload the main method by specifying different argument types. For example -

2 main methods with different arguments is perfectly legal

public static void main();
public static void main(String[] args);

The following are not legal as compiler will complain of duplicate methods

public static void main(String[] args);
public static void main(String[] args);

Even The following are not legal as we cannot overload on return types

public static String main(String[] args);
public static void main(String[] args);

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Q136. Can an application have multiple main methods within different classes ? If yes, How will the app decide which one to be executed ?

Core Java

Ans. Yes we can have a main method with string[] argument in every class of an application. When we execute an app we specify the starting point i.e the class that will get the control first and hence main method of that class gets executed.

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Q137. Which environment variables do we need to set in order to run Java programs?

Core Java

Ans. PATH, CLASSPATH and JAVA_HOME

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Q138. Scale yourself on Java on the scale of 1 to 10

General

Ans. [Open Ended Answer]

The objective of the question is to check how efficient one is in the language so that appropriate level questions are asked. Don't tell too high number if you are being interviewed for a junior or mid level position as the interviewer may throw advance level questions.

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

Q139. 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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Q140. What are Inner , Outer , Left and Right Joins in SQL ?

Database

Ans. Inner join is the intersection of two tables on the condition defined by the where clause i.e will get records from both tables matched by a column.

Outer join is the union of two tables i.e will get all records from both tables and will put null in the columns where related records are not present.

Left Outer join is the left union of two tables i.e all records from the table on the left and values from the right table for related records else null for the columns from right table.

Right Outer join is the right union of two tables i.e all records from the table on the right and values from the left table for related records else null for the columns from left table.

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Q141. What is an exception and exception handling in Java ?

Core Java

Ans. An Exception in java is the occurrence during computation that is anomalous and is not expected.

Exception handling is the mechanism which is used to handle such situations.

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Q142. What is database Normalization ?

Database

Ans. https://en.wikipedia.org/wiki/Database_normalization

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Q143. Why java doesn't support multiple Inheritance ?

or

Explain Java Diamond Problem.

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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Q144. Which class is the root class of all Exceptions in Java ?

Ans. Throwable

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Q145. Does java supports operator overloading ?

Core Java

Ans. No

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Q146. What is Maven ?

Maven

Ans. Maven is a build automation tool used primarily for Java projects.

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Q147. Write a Program to print the positive and negative numbers separetly

Core Java

Ans. int[] arr = {1,-1,2,-3,3,-4,4,5,6,-5,-6,-7,-8,8,9,-9};
List positiveNumbers = new ArrayList<>();
List negativeNumbers = new ArrayList<>();
for(int i = 0; i < arr.length(); i ){
if(I < 0){
negativeNumbers.add(i);
} else {
positiveNumbers.add(i);
}
}

System.out.println("Positive Numbers:" + positiveNumbers);
System.out.println("Negative Numbers:" + negativeNumbers);

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Q148. What are Collection Classes ?

Core Java

Ans. Collections in java is a framework of classes that provides an abstracted data structure to store and manipulate the group of objects. Each class is unique in the way it stores , search , sort and modify the elements.

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Q149. What are fields that gets displayed when you execute "Top" command and briefly explain each field ?

Unix

Ans. PID - process identification number is an identification number that is automatically assigned to each process when it is created

USER - User Name

PR - PR is the process actual priority

NI is the nice value, which is a user-space concept.

VIRT -Virtual Image (kb). The total amount of virtual memory used by the task.

RES - Resident size (kb). The non-swapped physical memory a task has used.

SHR - Shared Mem size (kb). The amount of shared memory used by a task.

S - Process Status. The status of the task which can be one of:

D = uninterruptible sleep
R = running
S = sleeping
T = traced or stopped
Z = zombie

%CPU - % CPU usage

%MEM - % MEM Usage

TIME - Total CPU time the task has used since it started.

COMMAND - Command which was used to execute the process

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Q150. Write a unix command to find top 10 files by size ?

Unix

Ans. du -a /var | sort -n -r | head -n 10

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