Help using String and character analyzers such as isDigit() and isLetter()

For some reason the isDigit and isLetter are giving me an error.

PasswordReTest.java:41: cannot find symbol
symbol : method isLetter(int)
location: class java.lang.String
if (p.isLetter(i))

and

PasswordReTest.java:43: cannot find symbol
symbol : method isDigit(int)
location: class java.lang.String
if (p.isDigit(i))

Code java:

import java.lang.*;
import javax.swing.*;
import java.io.*;
public class PasswordReTest
{
static String p = new String("P");
static String pp = new String("p");
static int len = 0;
static int letter = 0;
static int number = 0;
static int i = 0; 
static char ch;
public static void main(String[] args)
{
  passwordGet();
  passwordLengthTest();
  passwordCharTest();
	passwordValidate();
  JOptionPane.showMessageDialog(null, "Thank you for using the program");
}
 
public static void passwordGet()
{
 String p = new String(JOptionPane.showInputDialog(null,"Please Enter" +
 " Your Password: "));
}
 
public static void passwordLengthTest()
{
 len = p.length();
 if (len > 10 || len < 6)
   {
    JOptionPane.showMessageDialog(null, "Please make sure your password is" +
		" between 6 and 10 charcters long", "Error", JOptionPane.ERROR_MESSAGE);
    passwordGet();
   }
 else
   {
     for(int i = 0; i < len; i++);
     {
     if (p.isLetter(i))
         letter++;
     else if (p.isDigit(i))
         number++;
     else
     JOptionPane.showMessageDialog(null,"Invalid Charcter. Please enter only" + 
		 "letters & numbers", "Error", JOptionPane.ERROR_MESSAGE);
    }
   }
}
public static void passwordCharTest()
{
 if(letter <= 0)
  {   
   JOptionPane.showMessageDialog(null, "Error", "Your password must contain" +
	 " at least one Letter.", JOptionPane.ERROR_MESSAGE);
  }
 else if(number <= 0)
  {
  JOptionPane.showMessageDialog(null, "Error", "Your password must" +
	" contain at least one Digit", JOptionPane.ERROR_MESSAGE);
  }
 else
  {
  passwordValidate();
  }
}
public static void passwordValidate()
{
 String pp = new String(JOptionPane.showInputDialog(null, "Please enter the" + 
 " password again: "));
 if (pp.equals(p))
 JOptionPane.showMessageDialog(null,"Password Accepted :)");
}
}

Any ideas? Thanks in advance. :)