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Q1421. Why String is a class in Java ?

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Q1422. Describe SQL Joins

Ans. Oracle having following types of joins these are also called 8i joins. There are:

1. Equi (or) Inner join
2. Non Equi join
3.Self join
4.Outer join

Oracle also support the 9i (or) ANSI standard joins.There are:

1.Inner join
2.Left outer join
3.Right outer join
4.Full outer join
5.Natural join

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Q1423. How do you make instance of an abstract class ?

Ans. By extending it to the derived class and thereby creating instance of derived class.

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Q1424. How to see last 500 lines of a log or text file

Ans. tail -500 <FILE_NAME>

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Q1425. Write code for serialization.

Ans. // Java code for serialization and deserialization
// of a Java object
import java.io.*;

class Demo implements java.io.Serializable
{
   public int a;
   public String b;

   // Default constructor
   public Demo(int a, String b)
   {
      this.a = a;
      this.b = b;
   }

}

class Test
{
   public static void main(String[] args)
   {
      Demo object = new Demo(1, "geeksforgeeks");
      String filename = "file.ser";

      // Serialization
      try
      {
         //Saving of object in a file
         FileOutputStream file = new FileOutputStream(filename);
         ObjectOutputStream out = new ObjectOutputStream(file);

         // Method for serialization of object
         out.writeObject(object);

         out.close();
         file.close();

         System.out.println("Object has been serialized");

      }

      catch(IOException ex)
      {
         System.out.println("IOException is caught");
      }

      Demo object1 = null;

      // Deserialization
      try
      {
         // Reading the object from a file
         FileInputStream file = new FileInputStream(filename);
         ObjectInputStream in = new ObjectInputStream(file);

         // Method for deserialization of object
         object1 = (Demo)in.readObject();

         in.close();
         file.close();

         System.out.println("Object has been deserialized ");
         System.out.println("a = " object1.a);
         System.out.println("b = " object1.b);
      }

      catch(IOException ex)
      {
         System.out.println("IOException is caught");
      }

      catch(ClassNotFoundException ex)
      {
         System.out.println("ClassNotFoundException is caught");
      }

   }
}

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Q1426. Find all paths of length L in an acyclic graph

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Q1427. What are the drawbacks of creating immutable objects ? Why don't we create all object immutable if mutability possesses so much threat ?

Ans. Immutable objects relieves us from the problems of inconsistencies and security and helps with better read performance but at the same time are write performance and storage overheads. In case any modification is required , a new object is created and thus creating multiple copies of it.

This is the reason we use StringBuffer / StringBuilder when we have to append some text multiple times and then create a String out of it.

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Q1428. Does immutability facilitates better performance ?

Ans. Yes , but only the read performance in case we don't need to modify it much. In case we need to modify it a lot , it creates write performance overheads as we would need to create many news objects instead of just changing one.

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Q1429. How do you fetch the records form database ?

Ans. To fetch records from a database, you would use SELECT statements

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Q1430. Write a program to rotate array elements clockwise.

Ans. class Rotate{

void leftRotate(int arr[], int d, int n)
{
for (int i = 0; i < d; i )
leftRotatebyOne(arr, n);
}

void leftRotatebyOne(int arr[], int n)
{
int i, temp;
temp = arr[0];
for (i = 0; i < n - 1; i )
arr[i] = arr[i 1];
arr[i] = temp;
}

void printArray(int arr[], int n)
{
for (int i = 0; i < n; i )
System.out.print(arr[i] " ");
}

public static void main(String[] args)
{
Rotate rotate = new Rotate();
int arr[] = { 1, 2, 3, 4, 5, 6, 7 };
rotate.leftRotate(arr, 2, 7);
rotate.printArray(arr, 7);
}
}

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Q1431. Given an array with number 1 to n, find the missing numbers.

Ans. int main ()
{
int a []={1..n};
int miss=getMiss (a,n);
Printf ("%d",miss);
}
getMiss (int a [],int n){
int I,total;
total=(n 1)*(n 2);
for (i = 0; i < n; i++)
total -= a[i];
return total;
}

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Q1432. Write a program to find the 10th prime number.

Ans. import java.util.Scanner;
public class Prime
{
public static void main(String[] args)
{
Scanner sc = new Scanner(System.in);
System.out.print("Enter n to compute the nth prime number: ");
int nth = sc.nextInt();
int num, count, i;
num=1;
count=0;

while (count < nth){
num=num 1;
for (i = 2; i <= num; i )
{
if (num % i == 0)
{
break;
}
}
if ( i == num)
{
count = count 1;
}
}
System.out.println("Value of nth prime: " num);
}
}

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Q1433. Write a program to find length of String without using library function.

Ans. Class lengofstring {
Public static void main(String[] arr) {
int i = 0;
String s = "hello world!";
for (char C: s.toCharArray()) i;
System.out.println("Length: "
i);
}
}

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Q1434. Write a custom exception.

Ans. if you are creating your own exception is known as custom exception.

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Q1435. What is an exception ? What are the different types of exceptions ?

Ans. An exception is an unwanted or unexpected event, which occurs during the execution of a program that is at run time, that disrupts the normal flow of the program?s instructions. these are different types arithmetic exceptions, class not found exception, interrupted exception, run time exception etc.

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Q1436. Is HttpServlet an abstract class ?

Ans. Yes

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Q1437. Write code to read data from a file and write it to a file with 2 threads using the thread name content

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Q1438. Which are the thread safe / synchronized / concurrent classes in java collections ?

Ans. Stack
Properties
Vector
BlockingQueue
ConcurrentMap
ConcurrentNavigableMap

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Q1439. Can you write critical section code for singleton design pattern ?

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Q1440. Explain toString method ? Which class contains this method ?

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Q1441. What will the following code print and Why

class Class1 {
static{
System.out.println("Wow");
}
public static final int xyz=1;
}

class Class2{
public static void main(String[] args) {
System.out.println(String.valueOf(Class1.xyz));
}
}

Ans. 1

Reason being that Class1.xyz is replaced with 1 during pre compilation only and a reference to Class1 is never made.

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Q1442. Why do we have multiple core java jars in java 9 ?

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Q1443. What is the concept of modules in Java 9 ?

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Q1444. How modules are different than packages in Java 9 ?

Ans. Modules are independently build units and contains multiple packages.

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Q1445. How Java 9 helps in building light weight applications ?

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Q1446. Do we need different class loaders for different modules in Java 9 ?

Ans. No, We can use the same class loader.

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Q1447. What is ModuleDescriptor ?

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Q1448. What is ModuleLayer ?

Ans. A Module layer is created from a graph of modules and is a function that maps modules to their class loaders.

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Q1449. Difference between named and unnamed modules ?

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Q1450. What is the use of Requires, Exports, Opens and provides within Module Descriptor ?

Ans. Requires specifies the dependencies for the module, i.e the modules required for this module to function.

Exports specifies the packages exported by the module.

Opens specifies the packages opened by the module.

Provides specifies the services provided by the module

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