Nearest prime number to any number

class NearestPrime
{
public void n_prime(int n)
{
int up,dn,i;
up=n+1;

      while(true)
      {
          i=isprime(up);
          if(i==0)
          break;
          up++;
       }
              dn=n-1;
              while(true)
              {
                  i=isprime(dn);
                  if(i==0)
                  break;
                  dn--;
               }
                System.out.print("the nearest prime number is");
                  if((n-dn)<(up-n))
                  System.out.println(dn);
                  else if((up-n)<(n-dn))
                 System.out.println(up);
                 else
                 System.out.println(up+" "+dn);
 }             
    
              public int isprime(int a)
              {   int f=0;
                  for(int j=2;j<=a/2;j++)
                  {
                      if (a%j==0)
                      {
                          f=1;break;
                        }}
                        return f;
                    }
                }