Real Number DFA

gistfile1.java

import java.io.*;
public class Real
{
	public static void main(String[] args)
	{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String in;
		try{
			System.out.println("Enter string");
			in = br.readLine();
			fa(in);
		}
		catch(IOException e)
		{
			System.err.println(e.toString());
		}	
	}
	public static boolean isNum(char foo)
	{
		return (foo >= '0' && foo <= '9');
	}
	public static void fa(String in)
	{
		int state = 0;
		for(int i = 0; i<in.length(); i++)
		{
			char foo = in.charAt(i);
			
			switch(state){
				case 0:
				if(isNum(foo))
					state = 1;
				else if(foo == '+' || foo == '-')
					state = 1;
				else
					state = -1;
				break;
				
				case 1:
				if(isNum(foo))
					state = 1;
				else if(foo == '.')
					state = 7;
				else if(foo == 'e' || foo == 'E')
					state = 4;
				else
					state = -1;
				break;	
				
				case 3:
				if(isNum(foo))
					state = 3;
				else if(foo == 'e' || foo == 'E')
					state = 4;
				else
					state = -1;
				break;
				
				case 4:
				if(isNum(foo))
					state = 5;
				else if(foo == '+' || foo == '-')
					state = 6;
				else
					state = -1;
				break;
				
				case 5:
				if(isNum(foo))
					state = 5;
				else 
					state = -1;
				break;
				
				case 6:
				if(isNum(foo))
					state = 5;
				else
					state = -1;
				break;
				
				case 7:
				if(isNum(foo))
					state = 3;
				else
					state = -1;
			}
			if(state == -1)
				break;
			System.out.println("State: "+state+" "+foo);
		}
		if(state==1||state==3||state==5)
			System.out.println("Valid Real Number.");
		else
			System.out.println("Invalid String.");
		
	}
}