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Q441. How are values passed in Java ? By value or reference ?

Core Java

Ans. Java only provides pass by value.

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Q442. What will happen if we call perform(null) ?

public void perform(Object obj) {
System.out.println("Object");
}

public void perform(Integer int) {
System.out.println("Integer");
}

Core Java

Ans. compiler will throws error as ambiguous methods

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Q443. What will be the output of following code ?

System.out.println((int)'a');

Ans. The ascii value of a i.e 97

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Q444. What will be the output of

System.out.println((Integer)'a');

Ans. It will result in compilation error as primitive char cannot be casted to Integer object, alternatively we can cast it to primitive int like following

System.out.println((int)'a');

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Q445. What is a package and what are its advantages ?

Core Java

Ans. Package is a namespace that organizes a set of related classes.

Advantages of Packages

1. Better Organization of classes.
2. Saves from the problem of duplicate names as duplicate class names are allowed across different packages.

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Q446. What is a Database Trigger ?

Database

Ans. A trigger is a special kind of stored procedure that automatically gets executed upon an event in the database server.

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Q447. Have you heard about the external table feature of Oracle ?

Database

Ans. The external tables feature is a complement to existing SQL Loader functionality. It enables to access data in external sources as if it were in a table in the database. We have used it few times for replicating tables across different database systems.

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Q448. Can we have two beans with same class with different bean id in spring ?

Spring

Ans. Yes

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Q449. What is the use of Deprecated annotation ?

Ans. Deprecated annotation is for documentation purpose only. It doesn't enforce anything but would mark the method name as crossed to signify that the client should refrain from using it.

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Q450. Does Deprecated annotation enforces anything ?

Ans. No. It just marks the method and hence signals the client to refrain from using it.

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Q451. What is a self Join and give an example of a self Join ?

or

What is self Join and What is it's purpose ?

Database

Ans. When a Table Join itself , it's a Self Join. For example - we like to know the pair of department names where first dept has lesser employees than the later.

Select D1.name , D2.name from Dept D1, Dept D2 where D1.employee_count < D2.employee_count

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Q452. What was the driving force to introduce default methods in Interfaces wef from Java 8 ?

Core Java

Ans. Earlier any class implementing an interface was supposed to implement all methods declared in an interface. There was no place for optionally implementing all or subset of methods.Though we have abstract classes wherein we could have provided such a mechanism by declaring some methods as abstract while providing definition for some. But as Abstract classes have a body and are comparatively heavier than interfaces and interfaces associate closely to the concept of providing interfacing than abstract classes, Java might have though of providing optional implementation for default methods. This way same interface can be reused in variety of ways rather than making copies of an interface to suit different needs.

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Q453. What is a stable build ?

Jenkins

Ans. A build is considered stable if it was built successfully and no publisher reports it as unstable.

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Q454. What are design situations to use Singleton and Prototype Design Pattern ?

Design

Ans. Both are creational design patterns.

Singleton is used when we would like to reuse an object if object is not supposed to hold request or thread specific information. Inversely Prototype is used in situations where we would like to reuse the object information but the request / thread may require it own data to be persisted.

In short, Singleton is used in situations where we can live with single object being shared across multiple requests or threads whereas Prototype is used when we need duplicate copies of objects.

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Q455. What is System.in in Java ?

Core Java

Ans. It is an InputSream which is usually connected to the keyboard input of console program.

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Q456. What are the advantages and disadvantages of Factory Design Pattern ?

Design

Ans. Object Oriented Design Patterns is the science of identifying the pattern to make objects communicate in a way to effectively implement a Solution.

Factory Design Patterns is the pattern that recommends creation of separate Factory Object for creation of other object. So its like saying - If you want to create an object of ClassA, Talk to FactoryObject ( which is an object of FactoryClass ). FactoryObject in itself encapsulates the inputs and logic required to make the decision regarding the creation and construction of object.

Advantage of Factory Pattern - Loose Coupling and Segregation of Responsibilities. Now instead of hard binding the complete logic to decide the nature and shape of the object on the basis of some conditions, you are assigning the responsibility to some other object and hence making the relationship loosely coupled and hence main tenable.

Disadvantages - Before Understanding the Dis-advantages , we should understand that these patterns were chosen after a period of evolution and research and almost best fit for the required solution, otherwise these patterns would have easily been replaced by now.

Though the advantages of these pattern surpass the disadvantages keeping in mind the decreasing cost of resources and increasing scale of applications, but still loose coupling by means of additional objects results in decreased performance.

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Frequently asked.

Q457. When does the finally block gets executed ?

Core Java

Ans. A finally block of code always executes, whether or not an exception has occurred.The only time finally won't be called is if you call System.exit() or if the JVM crashes first.

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Q458. How do you prefer to store money values in your application ?

Core Java

Ans. At Application level we use either Double or BigDecimal , preferably BigDecimal. At Database level we use Number with decimal precision 3.

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Q459. Explain System.out.println ?

Core Java

Ans. System is a class within java.lang package that contains several useful class fields and methods. It cannot be instantiated and hence can use only statically.even in this case this has been used statically i.e with class name itself and without creating an instance.

out is the static reference of Printstream declared as following in the System Class -

public final static PrintStream out = null;

println is the method of PrintStream class.

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Q460. Implement the following method ?

int findMax(int[] items)

Core Java

Ans. int findMax(int[] items){
   int maxNumber = 0;
   for(int x:items){
      if(x > maxNumber){
         maxNumber = x;
      }
   }

   return maxNumber;
}

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Very Frequently asked to Senior Software Engineers or Developers.

Q461. Describe some of the Design Patterns you have used ?

Design

Ans. [Open Ended Answer]

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Q462. If everything is an object , Cant we declare every object as

Object obj = new String();

Core Java

Ans. Yes, we can do that. Compiler wont complain. But using object reference we can only access methods which have been defined for object class i.e clone(), equals(), hashCode(), toString() etc.

We cannot access methods defined in String class or in any class in hierarchy between String and Object.

For example - we cannot do obj.append("abc") as it will now give compile time error.

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Q463. Which type of memory is cleaned / recovered by garbage collection - stack or heap ?

Core Java

Ans. Heap memory.

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Q464. Write a program to print all even numbers first and then all odd numbers till 100. For example the output should be
2
4
6
8
...... 100
and then
1
3
5
7
...... 99

using only 1 for loop ? Is it possible with just one loop ?

Core Java

Ans. Yes , It can be done using single for loop

public class BuggyBread{
public static void main (String args[]) {
   int x = 50;
   for(int i=1;i <= 100;i++){
      if(i<=50){
         System.out.println(i*2);
      } else {
         System.out.println(i-x);
         x = x - 1;
      }
   }
}
}

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Q465. Given two files with list of words, write a program to show the common words in both files

Core Java

Ans. import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.io.*;
public class Common {
public static void main(String ar[])throws Exception
   {
      File f=new File("a.txt");
File f1=new File("x.java");
      System.out.println(f.exists());
FileInputStream fin = new FileInputStream(f);
      FileInputStream fin1 = new FileInputStream(f1);

      byte b[]=new byte[10000];
byte b1[]=new byte[10000];
fin.read(b);
fin1.read(b1);
String s1 = new String(b);
String s2 =new String(b1);

String words1[] = s1.trim().split(" ");
String words2[] = s2.trim().split(" ");
Listlist1 = new ArrayList<>(Arrays.asList(words1));
Listlist2 = new ArrayList<>(Arrays.asList(words2));
list1.retainAll(list2);
System.out.println(list1);
}
}

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Q466. What is the difference between for and foreach loop in java ? Which one should be used in which cases ?

Core Java

Ans. 1. for loop in java is used with a counter as following

for(int counter=0;counter < 50;counter++){
System.out.println(list.get(counter));
}

for iterating and printing the contents of a collection

whereas foreach loop can be specified directly without the use of counter

for(String str:list){
System.out.println(list.get(counter));
}

2. for Each loop syntax is more clean if we have to iterate over the elements of a collection and we need not keep track of the record count

3. For is preferred when we need loops without the usage of collections or Array of objects and entirely primitives are being used

4. for loop is preferred if we need to keep track of record count and have to perform some action of the basis of that. For example - If we have to print something after every 5 records, With for each loop in such case, we will have to keep a separate counter.

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Q467. Does java supports operator overloading ?

Core Java

Ans. No

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Q468. What is database Normalization ?

Database

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

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Q469. When is the situation when finally section won't execute ?

Core Java

Ans. If the process / app is abruptly killed or terminated.

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Q470. What is the use of static keyword in Java ?

Core Java

Ans. static keyword is used to specify that the respective programming construct ( method , variable ) belongs to the class and not to its instance and is supposed to be shared by all instances of the class.

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