Reverse element of an array

public class ArrayReverse {

public static void main(String[] args) {
// Reverse element of an array

int[] arr = new int[4];

System.out.println("// Reverse element of an array");
for(int k=0; k<arr.length; k++)
{
arr[k] = (int) (Math.random()*100);
System.out.print(" " +arr[k]);
}
System.out.println();
System.out.print("------------");

for(int i=0; i<arr.length/2; i++)
{
int temp = arr[i];
arr[i] = arr[arr.length - 1-i];
arr[arr.length - 1-i] = temp;
}
System.out.println();

for(int j=0; j<arr.length; j++)
{
System.out.print(" " +arr[j]);
}
}
}
Output:

Find smallest and largest value in a given array

public class ArrayEx {

public static void main(String[] args) {
// TODO Auto-generated method stub

// find smallest and largest value in a array
int[] arr = {11,22, 33, 44, 55};

int smallest=999;
int largest=0;

System.out.println("// find smallest and largest value in a array\n");

for(int i=0; i<arr.length; i++ )
{
// find largest values
if(largest<arr[i]){
largest = arr[i];
}
// find smallest values
if(smallest>arr[i]){
smallest = arr[i];
}
}
System.out.println(largest);
System.out.println(smallest);
}
}

Output:

Block initialization in a java

Blocks.java

public class Blocks {

public int i=10;
public static int j=20;

public Blocks(){
System.out.println("1");
}

public void f1(){
System.out.println("2");
}

{
System.out.println("IB");
}

{
System.out.println("SIB");
}
}

MyProgram.java
public class MyProgram {

public static void main(String[] args) {
// TODO Auto-generated method stub

System.out.println("// Block initialization in a java ");

Blocks b1 = new Blocks();

System.out.println(b1.i);
System.out.println(Blocks.j);

b1.f1();
}
}

Output:

Prime numbers given in a range

public class PrimeNumber {

public static void main(String[] args) {
// TODO Auto-generated method stub

int i =0;
       int num =0;
       //Empty String
       String  primeNumbers = "";

       for (i = 1; i <= 100; i++)       
       {    
          int counter=0;  
          for(num =i; num>=1; num--)
  {
             if(i%num==0)
     {
counter = counter + 1;
     }
  }
  if (counter ==2)
  {
     //Appended the Prime number to the String
     primeNumbers = primeNumbers + i + " ";
  }
       }
       System.out.println("Prime numbers from 1 to 100 are :");
       System.out.println(primeNumbers);
   }
}
Output:

Armstrong number

public class ArmstrongNumber {

public static void main(String[] args) {
// TODO Auto-generated method stub

// Armstrong number

int num= 153;
int temp = num;
int sum = 0;
System.out.println("// Armstrong number\n");
while (num>0)
{
int l = num%10;
sum = sum +(l*l*l);
num = num/10;
}
if (temp == sum)
{
System.out.println("Armstrong number: "+temp);
}
else
{
System.out.println("Not armstrong number: "+temp);
}
}
}
Output:

Number series

public class Series {

public static void main(String[] args) {

// Print 8 16 10 20 12 24 14 .. 10 elements of the series

int i = 8;
int j = 16;
int count = 0;
System.out.print("// Print 8 16 10 20 12 24 14 .. 10 elements of the series\n");
while (count<=9)
{
System.out.print(" "+i);
System.out.print(" "+j);
i = i+2;
j = j+4;
count++;
}

System.out.print("\n\n");
// Print 33 37 41 .. 10 elements of the series

int k = 33;
int counter = 0;

System.out.print("// Print 33 37 41 .. 10 elements of the series\n");
while (counter<=9)
{
System.out.print(" "+k);
k = k+4;
counter++;
}
}
}
Output:

Palindrome number

public class Palindrom {

public static void main(String[] args) {
// TODO Auto-generated method stub

// Palindrome number
int num=151;
int temp=num;
int rev=0;

System.out.println("// Palindrome number");
while(num>0){
int last = num%10;
rev = (rev*10)+last;
num = num/10;
}
if(temp==rev)
{
System.out.println("Number is Palindrom number");
}
else
{
System.out.println("Not a Palindrom number");
}
}
}
Output:

Prime number

public class PrimeNumber {

public static void main(String[] args) {
// TODO Auto-generated method stub
// Prime number
int num = 13;
int i=2;
int temp=num;
boolean isPrime=true;

System.out.println("// Prime number");
while(i<num-1)
{
if(num%i==0)
{
isPrime=false;
break;
}
i++;
}
if(isPrime == false)
{
System.out.println("Number not a prime number");
}
else
{
System.out.println("Number is Prime number");
}
}
}

Output:

Fibonacci series

public class FibonacciNumber {

public static void main(String[] args) {
// TODO Auto-generated method stub

int first=0;
int second=1;
// Fibonacci series
System.out.print("// Fibonacci series\n");
System.out.print(" " +first);
System.out.print(" " +second);

int sum = first + second;

while (sum<=100)
{
System.out.print(" " +sum);
first = second;
second = sum;
sum = first + second;
}
}
}
Output:

Core Java pattern programs

import java.util.Scanner;

public class Pattern {

public static void main(String[] args) {
// TODO Auto-generated method stub

int num=0;
//Pattern example
//Taking input from keyboard
Scanner sc = new Scanner(System.in);
System.out.println("Enter the row number");
num = sc.nextInt();

System.out.println("// Pattern \n");
for(int i=0; i<num;i++){
for(int j=0; j<=i;j++){
System.out.print("*");
}
System.out.print("\n");
}
}
}
Output:

import java.util.Scanner;

public class Pattern1 {

public static void main(String[] args) {
// TODO Auto-generated method stub
int num=0;
//Pattern1 example
//Taking input from keyboard
Scanner sc = new Scanner(System.in);
System.out.println("Enter the row number");
num=sc.nextInt();

System.out.println("// Pattern1 \n");
for(int i=0; i<num;i++)
{
for(int j=num; j>i;j--)
{
System.out.print("*");
}
System.out.print("\n");
}
}
}
Output:

import java.util.Scanner;

public class Pattern2 {

public static void main(String[] args) {
// TODO Auto-generated method stub

int num=0;
//Pattern2 example
//Taking input from keyboard
Scanner sc = new Scanner(System.in);
System.out.println("Enter the row number");
num=sc.nextInt();

System.out.println("// Pattern2 \n");
for(int i=1; i<=num;i++)
{
for(int j=1; j<=i;j++)
{
System.out.print(j);
}
System.out.print("\n");
}

}

}

Output:

See full: Core Java Pattern Programs

import java.util.Scanner;

public class Pattern3 {

public static void main(String[] args) {

// TODO Auto-generated method stub

int num=0;

int count = 1;

//Pattern3 example

//Taking input from keyboard

Scanner sc = new Scanner(System.in);

System.out.println("Enter the row number");

num=sc.nextInt();

System.out.println("// Pattern3 \n");

for(int i=1; i<=num;i++)

{

for(int j=1; j<=i;j++)

{

System.out.print(count+" ");

count++;

}

System.out.print("\n");

}

}

}

Output:

import java.util.Scanner;

public class Pattern4 {

public static void main(String[] args) {

// TODO Auto-generated method stub

int num=0;

//Pattern4 example

//Taking input from keyboard

Scanner sc = new Scanner(System.in);

System.out.println("Enter number of rows");

num = sc.nextInt();

System.out.println("// Pattern4 \n");

for(int i=1; i<=num;i++)

{

char ch = 'a';

for(int j=1; j<=i;j++)

{

System.out.print(ch);

ch++;

}

System.out.print("\n");

}

}

}

Output:

import java.util.Scanner;

public class Pattern5 {

public static void main(String[] args) {

// TODO Auto-generated method stub

int num=0;

char ch = 'a';

//Pattern5 example

//Taking input from keyboard

Scanner sc = new Scanner(System.in);

System.out.println("Enter number of rows");

num = sc.nextInt();

System.out.println("// Pattern5 \n");

for(int i=1; i<=num;i++)

{

for(int j=1; j<=i;j++)

{

System.out.print(ch);

ch++;

}t

System.out.print("\n");

}

}

}

Output:

See full: Core Java Pattern Programs

import java.util.Scanner;

public class Pattern6 {

public static void main(String[] args) {

// TODO Auto-generated method stub

int num=0;

//Pattern6 example

//Taking input from keyboard

Scanner sc = new Scanner(System.in);

System.out.println("Enter number of rows");

num = sc.nextInt();

System.out.println("// Pattern6 \n");

for(int i=1; i<=num;i++)

{

for(int j=1; j<=num;j++)

{

if(i+j>num){

System.out.print("*");

}else

{

System.out.print(" ");

}

}

System.out.print("\n");

}

}

}

Output:

import java.util.Scanner;

public class Pattern7 {

public static void main(String[] args) {
// TODO Auto-generated method stub

int num=0;
//Pattern7 example
//Taking input from keyboard
Scanner sc = new Scanner(System.in);
System.out.println("Enter number of rows");
num = sc.nextInt();

System.out.println("// Pattern7 \n");
for(int i=1; i<=num; i++)
{
for(int j=1; j<=num; j++)
{
System.out.print(i);
}
System.out.print("\n");
}
}

}

Output:

import java.util.Scanner;

public class Pattern8 {

public static void main(String[] args) {

// TODO Auto-generated method stub

int num=0;

//Pattern8 example

//Taking input from keyboard

Scanner sc = new Scanner(System.in);

System.out.println("Enter number of rows");

num = sc.nextInt();

System.out.println("// Pattern8 \n");

for(int i=1; i<=num; i++)

{

for(int j=1; j<=(num+i)-1; j++)

{

if(i+j<(num+1)){

System.out.print(" ");

}else

{

System.out.print("*");

}

}

System.out.print("\n");

}

}

}

Output:

 import java.util.Scanner;

public class Pattern9 {

public static void main(String[] args) {
// TODO Auto-generated method stub

int start=0;
int end=0;
//Pattern9 example
for(int i=1; i<=4; i++)
{
start = i;
end = 8-i;
for(int j=1; j<8; j++)
{
if(j<=start || j>=end){
System.out.print("*");
}else{
System.out.print(" ");
}
}
System.out.print("\n");
}

}

}

Output:

See full: Core Java Pattern Programs

Reverse string using different way

import java.util.Scanner;

public class ReverseDemo {

public static void main(String[] args) {
// TODO Auto-generated method stub

Scanner sc = new Scanner(System.in);
System.out.println("Please enter string");
String s = sc.nextLine();

// Simple use charAt method
System.out.print("// Simple use charAt method\n");
for(int i=s.length()-1; i>=0; i--){
System.out.print(s.charAt(i));
}
System.out.println("\n");

// Use charArray
System.out.print("// Use charArray\n");
char ch[] = s.toCharArray();
for(int i=ch.length-1; i>=0; i--)
{
System.out.print(ch[i]);
}
System.out.println("\n");

// Use StringBuilder
System.out.print("// Use StringBuilder and charArray\n");
StringBuilder sb = new StringBuilder();
for(int i=ch.length-1; i>=0; i--)
{
sb.append(ch[i]);
}
System.out.print(""+sb.toString());

System.out.println("\n");

// Use StringBuilder and reverse method
System.out.print("// Use StringBuilder and reverse method\n");
StringBuilder sbr = new StringBuilder(s);
String str = sbr.reverse().toString();
System.out.print(str);

System.out.println("\n");

// Reverse using recursion no inbuilt method
System.out.print("// Reverse using recursion no inbuilt method\n");
char str1[] = null;
str1 = s.toCharArray();
int size = str1.length;
reverse(str1, 0, size - 1);
System.out.print(str1);
}

public static void reverse(char str[], int stringIndex, int stringSize){

char temp;

temp = str[stringIndex];
str[stringIndex] = str[stringSize - stringIndex];
str[stringSize - stringIndex] = temp;

if (stringIndex == stringSize / 2)
{
return;
}

// Use recursion
reverse(str, stringIndex + 1, stringSize);
}
}

Output: