CONVERT DECIMAL NO. TO ITS BINARY, OCTAL & HEXADECIMAL EQUIVALENT

import java.io.*;
class DecimalConvert
{
static int n=0;
static void D2B()
{
int a[]=new int[10];
int d,copy=n,i=0;
while(copy>0)
{
d=copy%2;
a[i++]=d;
copy/=2;
}
//display
System.out.println("NO. IN BINARY: ");
for(--i;i>=0;i--)
System.out.print(a[i]);
System.out.println();
}

static void D2O()
{
int a[]=new int[10],d,copy=n,i=0;
while(copy>0)
{
d=copy%8;
a[i++]=d;
copy/=8;
}
//display
System.out.println("NO. IN OCTAL: ");
for(--i;i>=0;i--)
System.out.print(a[i]);
System.out.println();
}

static void D2H()
{
int a[]=new int[10],d,copy=n,i=0;
while(copy>0)
{
d=copy%16;
a[i++]=d;
copy/=16;
}
//display
System.out.println("NO. IN HEXADECIMAL: ");
for(--i;i>=0;i--)
{
if(a[i]<10)
System.out.print(a[i]);
else
System.out.print((char)(55+a[i]));
}
}
public static void main()throws IOException
{
BufferedReader in=new BufferedReader(new InputStreamReader(System.in));
System.out.print("ENTER THE DECIMAL NO.-");
n=Integer.parseInt(in.readLine());
D2B();
D2O();
D2H();
}
}

Twin Prime

import java.io.*;
import java.lang.*;
class Twin_Prime
{
private int n;
BufferedReader in=new BufferedReader(new InputStreamReader(System.in));

public void accept()throws IOException
{
System.out.println("Enter the Number: ");
n=Integer.parseInt(in.readLine());
}

public void calculate()
{
int i=n,j=n,x=0;

if((primeCheck(n-1)==true)&&(primeCheck(n+1))==true)
{
System.out.println("("+(n-1)+", "+(n+1)+")");
return;
}

for(;;i++)
  if((primeCheck(i)==true)&&(primeCheck(i+2))==true)
  break;

for(;j>0;j--)
if((primeCheck(j)==true)&&(primeCheck(j-2))==true)
break;
//int x=minimum((i-n),(n-j));
if((i-n)<(n-j))x=i;
else if((i-n)>(n-j))x=j;
else
{
System.out.println("("+i+", "+(i+2)+")");
System.out.println("("+(j-2)+", "+j+")");
}

if(x==i)
System.out.println("("+i+", "+(i+2)+")");
if(x==j)
System.out.println("("+(j-2)+", "+j+")");
}

public boolean primeCheck(int z)
{
for(int k=2;k<=z/2;k++)
if(z%k==0)
return false;

return true;
}

public void main(String args[])throws IOException
{
Twin_Prime ob=new Twin_Prime();
ob.accept();
ob.calculate();
}
}