Java Programming

Hello everyone,

I've just started with Java recently, and i'm just trying to code some in Java. I came up with this idea for an app to convert decimal -> hexadecimal, decimal -> binary and vice versa. I managed to write the code for decimal -> binary

if ((radioButton1.getState() == true) && (radioButton5.getState() == true))
		{
        do
        {
        if (number % 2 == 0)
        result = "0" + result;
        else
        {
            result = "1" + result;
            number--;
        }
        number = number / 2;
        }
        while (number > 0);
        textField2.setText(result);
        }

I've also been working on decimal -> hexadecimal conversion

if ((radioButton1.getState() == true) && (radioButton6.getState() == true))
		{
	    int digit = number.charAt();
		if (digit>='a' || digit>='A')
		{
			if (digit=='a' || digit=='A')
				digit=10;
			else if (digit=='b' || digit=='B')
				digit=11;
			else if (digit=='c' || digit=='C')
				digit=12;
			else if (digit=='d' || digit=='D')
				digit=13;
			else if (digit=='e' || digit=='E')
				digit=14;
			else if (digit=='f' || digit=='F')
				digit=15;
		}
	     int bla = number / 16;  
	     int rest = number - bla;
	     resultaat = String.valueOf(rest+bla);
	     textField2.setText(resultaat);
		
		   
		}

The problem is, that the decimal -> hexadecimal conversion does not work. The error given is "Can't invoke a method on a int. int digit = number.charAt();

Now my question is, how do i get the dec->hex conversion working? And do you guys have some tips (guidelines) to point me in the right direction for the binary-> decimal conversion, cause i'm really stuck on that one.

Thanks alot in advance,

Kevin