Converting a data from one base to another

import java.io.*;
public class BaseConversion
{
    static BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    static String Orig_Num="",Conv_Num="",KeyNodes="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    static int Orig_Base=0,Conv_Base=0,Deci_Num=0,p=0,flag=0;
    private void input()throws Exception
    {
        do
        {   System.out.print("Enter the ORIGINAL NUMBER (ALPHA IN CAPS ONLY) : ");Orig_Num=br.readLine();
            Orig_Num=Orig_Num.toUpperCase();
            do
            {   flag=0;
                System.out.print("Enter the ORIGINAL Base : ");Orig_Base=Integer.parseInt(br.readLine());
                if((Orig_Base<2)||(Orig_Base>36))
                    {System.out.println("Invalid Base");flag=1;}
            }while(flag==1);
            if(!validate(Orig_Num,Orig_Base))
                {System.out.println("Invalid Character Of Valid Base Found");flag=1;}
        }while(flag==1);
        do
        {   flag=0;
            System.out.print("Enter the CONVERSION Base : ");Conv_Base=Integer.parseInt(br.readLine());
            if((Conv_Base<2)||(Conv_Base>36))
                {System.out.println("Invalid Base");flag=1;}
        }while(flag==1);
    }
  
    private boolean validate(String Num,int Base)
    {
        for(int i=0;i<Num.length();i++)
            if(KeyNodes.indexOf(Num.charAt(i))>=Base) return false;
        return true;
    }
  
    private void decimalConvert()
    {
        p=Orig_Num.length()-1;
        for(int i=0;i<Orig_Num.length();i++)
            Deci_Num+=((KeyNodes.indexOf(Orig_Num.charAt(i)))*(Math.pow(Orig_Base,p--)));
    }
  
    private void baseConvert()
    {
        do
        {   Conv_Num=(KeyNodes.charAt(Deci_Num%Conv_Base)+Conv_Num);
            Deci_Num/=Conv_Base;
        }while(Deci_Num>=1);
    }
  
    public static void main(String args[])throws Exception
    {
        BaseConversion obj=new BaseConversion();
        obj.input();obj.decimalConvert();if(!(Conv_Base==10))obj.baseConvert();
        System.out.println("\fOriginal  Number : "+Orig_Num+" :: Base : "+Orig_Base);
        if(!(Conv_Base==10)) System.out.println("Converted Number : "+Conv_Num+" :: Base : "+Conv_Base);
        else System.out.println("Converted Number : "+Deci_Num+" :: Base : "+Conv_Base);
    }
}