Printing Prime number in java

class PrimeNo{
    public static void main(String ar[]){
        int n=50;
        boolean isPrime=false;
        for(int i=3;i<=n;i++){
            for(int j=2;j<i;j++){
                if(i%j==0){ 
                    isPrime=false;
                    break;
                }
                else
                    isPrime=true;
            }
            if(isPrime)
                System.out.println(i+" is prime");
        }
    }
}
  

Pattern [* square ]

class Pattern2{
    public static void main(String ar[]){
        int n=20;
        for(int i=1;i<=n;i++){
            for(int j=1;j<=n;j++){
                if(i==1||i==n){
                    System.out.print(" *");
                }else if(j==1||j==n){
                    System.out.print(" *");
                }else{
                    System.out.print("  ");
                }
            }
            System.out.println("");
        }
    }
}
/*
 
 * * * * * * * * * * * * * * * * * * * * *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 *                                     *
 * * * * * * * * * * * * * * * * * * * *
 
 */

Pattern

class Pattern1{
    public static void main(String ar[]){
        char []chrs={'a','b','c','d','e','f','g','h','i','j','k','l','m'};
        for(int i=0;i<chrs.length;i++){
            for(int j=0;j<2*chrs.length;j++){
                if(j<=i||(2*chrs.length-j)<=i+1){
                    System.out.print(chrs[i]);
                }else{
                    System.out.print(" ");
                }
            }
            System.out.println("");
        }
    }
}

/* OUTPUT
a                        a
bb                      bb
ccc                    ccc
dddd                  dddd
eeeee                eeeee
ffffff              ffffff
ggggggg            ggggggg
hhhhhhhh          hhhhhhhh
iiiiiiiii        iiiiiiiii
jjjjjjjjjj      jjjjjjjjjj
kkkkkkkkkkk    kkkkkkkkkkk
llllllllllll  llllllllllll
mmmmmmmmmmmmmmmmmmmmmmmmmm

*/

GCD of two numbers

class Q1iPage139{
    static int a=20,b=30;
    public static void main(String ar[]){
        int x=test(6,18);
        System.out.println(x);
    }
    static int test(int a,int b){
        int gcd=0;
        int c=(a<b)?a:b;
        for(int i=1;i<=c;i++){
                if((a%i==0)&&(b%i==0)){
                    gcd=i;
                }
        }
        return gcd;
    }
}

Program to check palindrom of string

//Program to check palindrom of string
class Q4ipage154{
    public static void main(String ar[]){
        boolean b=pal("nitin");
        System.out.println(b);
    }
    static boolean pal(String s)
    {
        boolean p=true;
        int start=0,end=s.length()-1;
        while(start<end){
            if(!(s.charAt(start)==s.charAt(end))){
                p=false;
                break;
            }
            start++;
            end--;
        }
        return p;
    }
}

Pattern

class Q3apage246{
    public static void main(String ar[]){
        int n=4;
        int a[][]=new int [n][];
        int c=0;
        for(int i=0;i<n;i++){
            a[i]=new int[i+1];
            for(int j=0;j<n;j++){
                if(j<=i){
                    a[i][j]=c;
                    c++;
                }
            }
        }
        for(int i=0;i<n;i++){
            for(int j=0;j<n;j++){
                    if(j<=i){
                     System.out.print(a[i][j]);
                    }
            }
            System.out.println("");
        }
    }
}

OUTPUT

0
12
345
6789

Fibnacci series (rec)

class Fib{
    static int fib(int a)
    {
        if (a==1||a==2)
            return 1;
        else{
            int n=fib(a-1)+fib(a-2);
            return n;
        }
        
    }
    public static void main(String ar[])throws Exception {
        int a=10,i;
        for(i=1;i<=a;i++)
        {
            System.out.printf("%5d",fib(i));
        }
    }
}

Single digit sum

/*189=9
* 1+8+9=18
* 1+8=9 (output)
*/
class Main{
static int rem=0,s=0;
static void sum(int num){
s=0;
while(num>0){
rem=num%10;
num=num/10;
s=s+rem;
}
if(s>=10){
sum(s);
}
}
public static void main(String ar[]){
int d=1891;
sum(d);
System.out.println("Single Digit sum ="+s);
}
}

Patterns

class Pattern{
 public static void main(String ar[]){
  int n=5;
  for(int i=0;i<n;i++){
   for(int j=1;j<=(2*n);j++){
    int start=n-i;
    int end=n+i;
    if((j>=start)&&(j<=(end))){
     System.out.print(i+1);
    }
    else{
     System.out.print(" ");
    }
   }
   System.out.println("");
  }
 }
}

Patterns

class Pattern{
 public static void main(String ar[]){
  int n=20;
  for(int i=0;i<n;i++){
   for(int j=1;j<=(2*n);j++){
    int start=n-i;
    int end=n+i;
    if((j>=start)&&(j<=(end))){
     System.out.printf("%2d",i+1);
    }
    else{
     System.out.printf("%2s"," ");
    }
   }
   System.out.println("");
  }
 }
}

Printing 2D array using recurrence method

class Pattern2DArray{
import java.io.*;
class Matrix{
 static int i=0,j=0;
 public static void main(String ar[])throws IOException{
  int a[][]={{1,2,3},{2,2,2},{1,2,3}}; 
  printArray(a);
 }
 public static void printArray(int arr[][]){
  if(i>arr.length-1)
  {
   return;
  }
  else
  {
   System.out.print(" "+arr[i][j]);
   
   if(i<arr.length && j==arr[i].length-1){
    i++;
    j=0;
    System.out.println();
    printArray(arr);
   }else{
    j++;
    printArray(arr);
   }
  }
 }
}

Printing array using recurrence method

import java.io.*;
class PrintArray{
 static int i=0,j=0;
 public static void main(String ar[])throws IOException{
  int a[]={23,23,23,5,45,4,65,6,34,7,56,7,88,78,7,5,45,6,4}; 
  printArray(a);
 }
 public static void printArray(int arr[]){
  if(i>arr.length-1)
  {
   return;
  }
  else
  {
   System.out.println(" "+arr[i]);
   i++;
   printArray(arr);
  }
 }
}

Matrix operations

import java.io.*;
class Matrix{
 public static void main(String ar[])throws IOException{
  int a[][]={{1,2,3},{2,2,2},{1,2,3}};
  int b[][]={{1,2,3},{2,2,2},{1,2,3}};
  int c[][]=new int[3][3];
  /*
  BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
  System.out.println("First Array");
  for(int i=0;i<3;i++){
   for(int j=0;j<3;j++){
    System.out.println("Enter element of "+i+","+j);
    a[i][j]=Integer.parseInt(br.readLine());
   }
  }
  
  System.out.println("Second Array");
  for(int i=0;i<3;i++){
   for(int j=0;j<3;j++){
    System.out.println("Enter element of "+i+","+j);
    b[i][j]=Integer.parseInt(br.readLine());
   }
  }
  */
  //adding
  for(int i=0;i<3;i++){
   for(int j=0;j<3;j++){  
    c[i][j]=a[i][j]+b[i][j];
   }
  }
  
  System.out.println("First Array");
  for(int i=0;i<3;i++){
   for(int j=0;j<3;j++){
    System.out.print(a[i][j]+" "); 
   }
   System.out.println("");
  }
  System.out.println("Second Array");
  for(int i=0;i<3;i++){
   for(int j=0;j<3;j++){
    System.out.print(b[i][j]+" "); 
   }
   System.out.println("");
  }
  System.out.println("Addition of Arrays");
  for(int i=0;i<3;i++){
   for(int j=0;j<3;j++){
    System.out.print(c[i][j]+" "); 
   }
   System.out.println("");
  }
 }
}

LCM

class LCM{
 public static void main(String ar[]){ 
  int a=8,b=12;
  double x=((a*b)/gcd(a,b));
  System.out.println("LCM  = "+x);
 }
 static int gcd(int a,int b)
 {
  if (a>=b&&a%b==0)
   return(b);
  else if(a<b)
   return(gcd(b,a));
  else
   return(gcd(b,a%b));
 }
}

GCD

GCD

class GCD{
 public static void main(String ar[]){
  int x=gcd(12,16);
  System.out.println("gcd = "+x);
 }
 
 static int gcd(int a,int b)
 {
  if (a>=b&&a%b==0)
   return(b);
  else if(a<b)
   return(gcd(b,a));
  else
   return(gcd(b,a%b));
 }
}

Program to represent complex numbers and adding them

class ComplexNumber {
 int r=0;
 int i=0;
 String c;
 ComplexNumber(int r,int i){
  this.r=r;
  this.i=i;
  if(i>=0)
   c=""+r+"+"+i+"i";
  else
   c=""+r+i+"i";
 }
 public String toString(){
  return c;
 }
 public ComplexNumber add(ComplexNumber c){
  int r=this.r+c.r;
  int i=this.i+c.i;
  return new ComplexNumber(r,i);
 }
}
class Complex{
 public static void main(String ar[]) {
  ComplexNumber c1=new ComplexNumber(2,3);
  ComplexNumber c2=new ComplexNumber(1,-2);
  ComplexNumber c3=c1.add(c2);
  System.out.println(c1);
  System.out.println(c2);
  System.out.println(c3);
 }
}