AtomicInteger in Java

Posted by: Instanceofjava Posted date: 5:49 PM / comment : 0


  • Java.util.concurrent.atomic package provides very useful classes that support lock free and thread safe programming.
  • The main use of this class is an int value that may be updated automatically.
  • AtomicInteger has some useful methods. Before that lets see the some points about this class.
  • Commonly we will use this AtomicInteger to handle the counter that is accessible by different threads simultaneously.

Java.util.concurrent.atomic.AtomicInteger:

  1. public class AtomicInteger
  2. extends Number
  3. implements Serializable

AtomicInteger Class Constructors:


  • public AtomicInteger(): Creates a new AtomicInteger object with default value 0.
  1. AtomicInteger atomicInteger = new AtomicInteger();
  • public AtomicInteger(int initialValue): Creates a new AtomicInteger object with given initial  value.
  1. AtomicInteger atomicInteger = new AtomicInteger(10);


 AtomicInteger Class Methods:


 1.public final void set(int newValue):
  •  Sets given value to the object.

  Java Program to create AtomicInteger class object and sets some value.

  1. package com.instaceofjava;
  2.  
  3. import java.util.concurrent.atomic.AtomicInteger;
  4.  
  5. public class AtomicIntegerExample{
  6.  
  7. public static void main(String[] args) {
  8.  
  9. AtomicInteger atomicInteger = new AtomicInteger();
  10.  
  11.   System.out.println(atomicInteger);
  12.   atomicInteger.set(10);
  13.   System.out.println(atomicInteger);
  14.  
  15. }
  16.  
  17. }

Output:

  1. 0
  2. 10

2, public final void get():

  • Used to get current value.

Java Program to create AtomicInteger class object and sets some value and get.

  1. package com.instaceofjava;
  2.  
  3. import java.util.concurrent.atomic.AtomicInteger;
  4.  
  5. public class AtomicIntegerExample{
  6.  
  7. public static void main(String[] args) {
  8.  
  9. AtomicInteger atomicInteger = new AtomicInteger();
  10.  
  11.   System.out.println(atomicInteger.get());
  12.   atomicInteger.set(10);
  13.   System.out.println(atomicInteger.get());
  14.  
  15. }
  16.  
  17. }

Output:

  1. 0
  2. 10
3.public final int getAndSet(int newValue):
  • Automatically sets the given value and returns old value.

  Java Program which explains getAndSet(int x) method of AtomicInteger class

  1. package com.instaceofjava;
  2.  
  3. import java.util.concurrent.atomic.AtomicInteger;
  4.  
  5. public class AtomicIntegerExample{
  6.  
  7. public static void main(String[] args) {
  8.  
  9. AtomicInteger atomicInteger = new AtomicInteger();
  10.  
  11.    System.out.println(atomicInteger.get());
  12.  
  13.    atomicInteger.set(10);
  14.  
  15.    System.out.println(atomicInteger.get());
  16.  
  17.    System.out.println(atomicInteger.getAndSet(12));
  18.  
  19.    System.out.println(atomicInteger.get());
  20.  
  21. }
  22.  
  23. }

Output:

  1. 0
  2. 10
  3. 10
  4. 12



4.public final int incrementAndGet()
  • Automatically increments the value one and returns updated value

  Java Program which explains incrementAndGet() method of AtomicInteger class

  1. package com.instaceofjava;
  2.  
  3. import java.util.concurrent.atomic.AtomicInteger;
  4.  
  5. public class AtomicIntegerExample{
  6.  
  7. public static void main(String[] args) {
  8.  
  9. AtomicInteger atomicInteger = new AtomicInteger();
  10.  
  11.    System.out.println(atomicInteger.get());
  12.  
  13.    atomicInteger.set(10);
  14.  
  15.    System.out.println(atomicInteger.get());
  16.  
  17.    System.out.println(atomicInteger.incrementAndGet());
  18.  
  19.  
  20. }
  21.  
  22. }

Output:

  1. 0
  2. 10
  3. 11


How to create immutable class in java

Posted by: Instanceofjava Posted date: 11:11 PM / comment : 0

  • In Java String and all wrapper classes are immutable classes.
  • So how to create custom immutable class in java?
  • Lets see how to make a class object immutable.

  Immutable class:

  • Make class final so that it should not be inherited.
  • All the variables should be private so should not be accessible outside of class. 
  • Make all variables final so that value can not be changed.
  • A constructor to assign values to variables in class.
  • Do not add any setter methods.

1. Java Program to create custom immutable class object in java.

  1. package com.instaceofjava;

  3.  
  4. public final class ImmutableClass{
  5.   
  6. private final int a;
  7. private final int b;
  8.  
  9. ImmutableClass( int x, int y){
  10.  
  11.  a=x;
  12.  b=y; 

  14. } 
  15.  
  16. public getA(){
  17.  
  18.  return a;

  20. }
  21.  
  22. public getB(){
  23.  
  24.  return b;

  26. }
  27.  
  28. public static void main(String[] args) {
  29.  
  30. ImmutableClass obj= new ImmutableClass(10,20);
  31.  
  32. System.out.println("a="+obj.getA());
  33.  
  34. System.out.println("b="+obj.getB());
  35.  
  36. }
  37. }
Output:

  1. a=10
  2. b=20


String class in java: Immutable
  1. public final class String
  2.         implements java.io.Serializable, Comparable<String>, CharSequence
  3. {  
  4.   
  5. //String class variables

  7.   private final char value[];
  8.   private final int offset;
  9.   private final int count;
  10.   private int hash; // Default to 0
  11.   private static final ObjectStreamField[] serialPersistentFields =
  12.       new ObjectStreamField[0];
  13.   
  14. //String class constructor
  15. public String(String original) {
  16.  
  17.             int size = original.count;
  18.              char[] originalValue = original.value;
  19.              char[] v;
  20.              if (originalValue.length > size) {
  21.                 // The array representing the String is bigger than the new
  22.               // String itself.  Perhaps this constructor is being called
  23.                 // in order to trim the baggage, so make a copy of the array.
  24.                  int off = original.offset;
  25.                 v = Arrays.copyOfRange(originalValue, off, off+size);
  26.             } else {
  27.                  // The array representing the String is the same
  28.                  // size as the String, so no point in making a copy.
  29.                  v = originalValue;
  30.            }
  31.             this.offset = 0;
  32.              this.count = size;
  33.             this.value = v;
  34.         } 

  36. }



Java Program to find Sum of Digits

Posted by: Instanceofjava Posted date: 10:33 AM / comment : 3


1. Java Program to find sum of digits without using recursion.

  1. package com.instaceofjava;
  2. import java.util.Scanner;
  3.  
  4. public class SumOfDigits {
  5.  
  6. public static void main(String[] args) {
  7.  
  8. int number;
  9. Scanner in = new Scanner(System.in);
  10.  
  11. System.out.println("Please Enter a number");
  12.  
  13. number=in.nextInt(); 
  14.  
  15. int sum=0 ;
  16.  
  17. while(number!=0){
  18.  
  19. sum=sum+(number%10);
  20. number=number/10;
  21. }
  22.  
  23. System.out.println("Sum of Digits ="+sum);
  24.  
  25. }
  26. }
Output:

  1. Please Enter a number
  2. 123
  3. Sum of Digits=6


2. Java Program to find sum of digits using recursion.

  1. package com.instaceofjava;
  2. import java.util.Scanner;
  3.  
  4. public class SumOfDigits {
  5.  
  6. int sum;

  8. public int CalRecSum(int n){
  9.  
  10. if(n==0){
  11. return sum;
  12. }
  13. else{
  14.  
  15.  sum+=n%10;
  16.  CalRecSum(n/10);
  17.  
  18. } 
  19.  
  20. return sum;
  21. }

  23. public static void main(String[] args) {
  24.  
  25. int number;
  26. Scanner in = new Scanner(System.in);
  27.  
  28. System.out.println("Please Enter a number");
  29.  
  30. number=in.nextInt(); 
  31.  
  32. SumOfDigits   ob= new SumOfDigits();
  33. System.out.println("Sum of Digits ="+ob.CalRecSum(number));
  34.  
  35. }
  36.  
  37. }


Output:

  1. Please Enter a number
  2. 326
  3. Sum of Digits=11

Swap two numbers without using third variable

Posted by: Instanceofjava Posted date: 1:23 AM / comment : 3

1. Java Interview Program to Swap two numbers without using third variable in java



  1. package com.instaceofjava;
  2.  
  3. public class SwapTwoNumbers {
  4.  
  5. public static void main(String[] args) {
  6.  
  7. int number1=20;
  8. int number2=30;
  9.  
  10. System.out.println("Before Swapping");
  11. System.out.println("Value of number1 is :" + number1);
  12. System.out.println("Value of number2 is :" +number2); 
  13.  
  14. number1=number1+number2;
  15. number2=number1-number2;
  16. number1=number1-number2;
  17.  
  18. System.out.println("After Swapping");
  19. System.out.println("Value of number1 is :" + number1);
  20. System.out.println("Value of number2 is :" +number2);
  21.  
  22. }
  23. }
Output:

  1. Before Swapping
  2. Value of number1 is :20
  3. Value of number2 is :30
  4. After Swapping
  5. Value of number1 is :30
  6. Value of number2 is :20

2. Java Program to Swap two numbers by using division and multiplication.


  1. package com.instaceofjava;
  2.  
  3. public class SwapTwoNumbers {
  4.  
  5. public static void main(String[] args) {
  6.  
  7. int number1=20;
  8. int number2=30;
  9.  
  10. System.out.println("Before Swapping");
  11. System.out.println("Value of number1 is :" + number1);
  12. System.out.println("Value of number2 is :" +number2); 
  13.  
  14. number1=number1*number2;
  15. number2=number1/number2;
  16. number1=number1/number2;
  17.  
  18. System.out.println("After Swapping");
  19. System.out.println("Value of number1 is :" + number1);
  20. System.out.println("Value of number2 is :" +number2);
  21.  
  22. }
  23. }


Output:

  1. Before Swapping
  2. Value of number1 is :20
  3. Value of number2 is :30
  4. After Swapping
  5. Value of number1 is :30
  6. Value of number2 is :20


3. Java Program to Swap two integers by using bit wise operators


  1. package com.instaceofjava;
  2.  
  3. public class SwapTwoNumbers {
  4.  
  5. public static void main(String[] args) {
  6.  
  7. int number1=2;
  8. int number2=4;
  9.  
  10. System.out.println("Before Swapping");
  11. System.out.println("Value of number1 is :" + number1);
  12. System.out.println("Value of number2 is :" +number2); 
  13.  
  14. number1=number1^number2;
  15. number2=number1^number2;
  16. number1=number1^number2;
  17.  
  18. System.out.println("After Swapping");
  19. System.out.println("Value of number1 is :" + number1);
  20. System.out.println("Value of number2 is :" +number2);
  21.  
  22. }
  23. }
Output:

  1. Before Swapping
  2. Value of number1 is :2
  3. Value of number2 is :4
  4. After Swapping
  5. Value of number1 is :4
  6. Value of number2 is :2


HashSet class

Posted by: Instanceofjava Posted date: 12:54 PM / comment : 0


Hierarchy of HashSet class:


 

 public class HashSet<E>
        extends AbstractSet<E>
           implements Set<E>, Cloneable, java.io.Serializable

Key points:

  • HashSet is sub class of AbstractSet class.
  • Underlying data structure of HashSet is HashTable.
  • HashSet implements Serializable and Cloneable interfaces
  • HashSet does not allow duplicate elements.
  • Insertion order is not preserved. No order(Based on hashcode of objects)



Constructors of HashSet:

1.HashSet( )
  • Creates an empty HashSet object with default initial capacity 16.  Fill ratio or load factor 0.75
2.HashSet(Collection obj)
  • This constructor initializes the hash set by using the elements of the collection obj.
3.HashSet(int capacity)
    • Creates an empty HashSet object with given capacity.
      4.HashSet(int capacity, float fillRatio)
      • This constructor initializes both the capacity and the fill ratio (also called load capacity) of the hash set from its arguments (fill ratio 0.1 to 1.0)

      Reverse words in a String

      Posted by: Instanceofjava Posted date: 12:13 AM / comment : 0

      1. Java Interview Program to Reverse words in a string


      1. package com.instaceofjava;
      2.  
      3. public class ReverseString {
      4.  
      5. public static void main(String[] args) {
      6.  
      7. String strng= "Instance of Java ";
      8.  
      9. String str[] =strng.split(" ");
      10.  
      11. String result="";
      12.  
      13. for(int i=str.length()-1;i>=0;i--){
      14.  
      15. result += str[i]+" ";
      16.  
      17. }
      18.  
      19. System.out.println(result );
      20. }
      21. }
      Output:

      1. Java of Instance



      2. Java Interview Program to Reverse words in a string


      1. package com.instaceofjava;
      2.  
      3. public class ReverseString {
      4.  
      5. public static void main(String[] args) {
      6.  
      7. String strng= "Instance of Java ";
      8.  
      9. StringBuilder sb = new StringBuilder(strng.length() + 1);
      10.  
      11.   String[] words = strng.split(" ");
      12.  
      13.   for (int i = words.length - 1; i >= 0; i--) {
      14.          sb.append(words[i]).append(' ');
      15.    }
      16.     
      17.     sb.setLength(sb.length() - 1); 
      18.  
      19.    String result= sb.toString();  
      20.  
      21.     System.out.println(result);

      23. }
      24. }
      Output:

      1. Java of Instance

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