InstanceOfJava

How to create immutable class in java

Posted by: Instanceofjava Posted date: December 24, 2015 / comment : 0 Java Programs

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.

package com.instaceofjava;
public final class ImmutableClass{
private final int a;
private final int b;
ImmutableClass( int x, int y){
a=x;
b=y;
}
public getA(){
return a;
}
public getB(){
return b;
}
public static void main(String[] args) {
ImmutableClass obj= new ImmutableClass(10,20);
System.out.println("a="+obj.getA());
System.out.println("b="+obj.getB());
}
}

Output:

a=10
b=20

String class in java: Immutable

public final class String
implements java.io.Serializable, Comparable<String>, CharSequence
{
//String class variables
private final char value[];
private final int offset;
private final int count;
private int hash; // Default to 0
private static final ObjectStreamField[] serialPersistentFields =
new ObjectStreamField[0];
//String class constructor
public String(String original) {
int size = original.count;
char[] originalValue = original.value;
char[] v;
if (originalValue.length > size) {
// The array representing the String is bigger than the new
// String itself. Perhaps this constructor is being called
// in order to trim the baggage, so make a copy of the array.
int off = original.offset;
v = Arrays.copyOfRange(originalValue, off, off+size);
} else {
// The array representing the String is the same
// size as the String, so no point in making a copy.
v = originalValue;
}
this.offset = 0;
this.count = size;
this.value = v;
}
}

Java Program to find Sum of Digits

Posted by: Instanceofjava Posted date: December 20, 2015 / comment : 3 Java Programs

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

package com.instaceofjava;
import java.util.Scanner;
public class SumOfDigits {
public static void main(String[] args) {
int number;
Scanner in = new Scanner(System.in);
System.out.println("Please Enter a number");
number=in.nextInt();
int sum=0 ;
while(number!=0){
sum=sum+(number%10);
number=number/10;
}
System.out.println("Sum of Digits ="+sum);
}
}

Output:

Please Enter a number
123
Sum of Digits=6

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

package com.instaceofjava;
import java.util.Scanner;
public class SumOfDigits {
int sum;
public int CalRecSum(int n){
if(n==0){
return sum;
}
else{
sum+=n%10;
CalRecSum(n/10);
}
return sum;
}
public static void main(String[] args) {
int number;
Scanner in = new Scanner(System.in);
System.out.println("Please Enter a number");
number=in.nextInt();
SumOfDigits ob= new SumOfDigits();
System.out.println("Sum of Digits ="+ob.CalRecSum(number));
}
}

Output:

Please Enter a number
326
Sum of Digits=11

Swap two numbers without using third variable

Posted by: Instanceofjava Posted date: December 19, 2015 / comment : 3 Java Programs

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

package com.instaceofjava;
public class SwapTwoNumbers {
public static void main(String[] args) {
int number1=20;
int number2=30;
System.out.println("Before Swapping");
System.out.println("Value of number1 is :" + number1);
System.out.println("Value of number2 is :" +number2);
number1=number1+number2;
number2=number1-number2;
number1=number1-number2;
System.out.println("After Swapping");
System.out.println("Value of number1 is :" + number1);
System.out.println("Value of number2 is :" +number2);
}
}

Output:

Before Swapping
Value of number1 is :20
Value of number2 is :30
After Swapping
Value of number1 is :30
Value of number2 is :20

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

package com.instaceofjava;
public class SwapTwoNumbers {
public static void main(String[] args) {
int number1=20;
int number2=30;
System.out.println("Before Swapping");
System.out.println("Value of number1 is :" + number1);
System.out.println("Value of number2 is :" +number2);
number1=number1*number2;
number2=number1/number2;
number1=number1/number2;
System.out.println("After Swapping");
System.out.println("Value of number1 is :" + number1);
System.out.println("Value of number2 is :" +number2);
}
}

Output:

Before Swapping
Value of number1 is :20
Value of number2 is :30
After Swapping
Value of number1 is :30
Value of number2 is :20

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

package com.instaceofjava;
public class SwapTwoNumbers {
public static void main(String[] args) {
int number1=2;
int number2=4;
System.out.println("Before Swapping");
System.out.println("Value of number1 is :" + number1);
System.out.println("Value of number2 is :" +number2);
number1=number1^number2;
number2=number1^number2;
number1=number1^number2;
System.out.println("After Swapping");
System.out.println("Value of number1 is :" + number1);
System.out.println("Value of number2 is :" +number2);
}
}

Output:

Before Swapping
Value of number1 is :2
Value of number2 is :4
After Swapping
Value of number1 is :4
Value of number2 is :2

HashSet class

Posted by: Instanceofjava Posted date: November 21, 2015 / 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: November 10, 2015 / comment : 0 Java Programs

1. Java Interview Program to Reverse words in a string

package com.instaceofjava;
public class ReverseString {
public static void main(String[] args) {
String strng= "Instance of Java ";
String str[] =strng.split(" ");
String result="";
for(int i=str.length()-1;i>=0;i--){
result += str[i]+" ";
}
System.out.println(result );
}
}

Output:

Java of Instance

2. Java Interview Program to Reverse words in a string

package com.instaceofjava;
public class ReverseString {
public static void main(String[] args) {
String strng= "Instance of Java ";
StringBuilder sb = new StringBuilder(strng.length() + 1);
String[] words = strng.split(" ");
for (int i = words.length - 1; i >= 0; i--) {
sb.append(words[i]).append(' ');
}
sb.setLength(sb.length() - 1);
String result= sb.toString();
System.out.println(result);
}
}

Output:

Java of Instance

Introducton to Spring

Posted by: Instanceofjava Posted date: September 20, 2015 / comment : 1 spring

Spring Framework history:

Spring was developed in June,2003
Initially developed by Rod Johnson.
Latest version of Spring Framework version 4.1.6 released in Mar 2015.

What is Spring:

Spring is Open Source Framework.
Spring is Lightweight Application Framework.
Spring is Simple framework.
Spring is loosely coupled.
Spring is a complete and a modular framework,because spring can be used in all layers of applications means front end(Spring MVC),Database(Spring JDBC,Spring ORM).

Why Spring:

Why Spring come in to picture is because of EJB fails,EJB having multiple configuration files,it is affected on performance.so spring came up.
Struts designed for Web Layer,like Other Frameworks also addressed specific layer,But Spring Framework provides solution to support all layers of application.
Spring is non invasive framework,means Spring doesn't force to implement or extend any class from predefined class from Spring API.

Advantages of Spring:

Spring is open source and lightweight framework.
Spring is supports all layers including web layer.
Easy for testing.
Spring Supports POJO Model.
POJO-Plain Old Java Object.
Spring works in simple Java environment,because it is non,invasive.
Spring can be integrated with any Application Server
Spring simplifies J2EE development.

Spring Modules:
spring 1.x have seven modules,but in 2.x on wards we have 6 modules.

Spring Core
Spring DAO(Spring JDBC)
Spring AOP(Ascept Orient Programming)
Spring ORM(Spring Hibernate)
Spring MVC
Spring WEB
Spring Context(J2EE)

Spring 2.x Modules:
from Spring 2.x ,Spring -WEB and Spring-MVC is combined.

Spring Core
Spring DAO(Spring JDBC)
Spring AOP(Ascept Orient Programming)
Spring ORM(Spring Hibernate)
Spring WEB-MVC
Spring Context(J2EE

Spring is combination of various modules Seven well defined modules,Most of them are reasonably independent.
Spring modules built using modular approach,you can use only required modules Each module is set of one or more JAR files
Spring’s core module is “Inversion of Control”(IoC) also known as “Dependency Injection”.
All other Spring modules are built on top of IoC.IoC is a Foundation or Container of Spring Framework.
Spring core module is the base module for all modules.

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