Polish notation JavaStackImpl

PrefixNotation.java

package prefixNotation;

public class prefix {

	/**
	 * @param args
	 */
	public static String reverse(String input){
		if(input.length()==1){
			return(input);
		}else{
			return(reverse(input.substring(1,input.length()))+input.charAt(0));
		}
	}
	public static double prefixEval(String input){
		java.util.Stack<Double> s = new java.util.Stack<Double>();
		//input
		System.out.println(input);
		input=reverse(input);
		int k2;
		String c;
		for(int k = 0 ; k < input.length() ; k++){
			c = input.substring(k,k+1);
			try{
				k2=0;
				while(!input.substring(k+k2,k+k2+1).equals("/") && !input.substring(k+k2,k+k2+1).equals("*") && !input.substring(k+k2,k+k2+1).equals("-") && !input.substring(k+k2,k+k2+1).equals("+") && !input.substring(k+k2,k+k2+1).equals(",")){
					k2++;
				}
				k+=k2;
				s.push(Double.parseDouble(reverse(input.substring(k-k2,k))));
				k--;
			}
			catch(Exception NumberFormatException){
				if(c.equals("+")){
					s.push(s.pop()+s.pop());
				}
				if(c.equals("-")){
					s.push(s.pop()-s.pop());
				}
				if(c.equals("/")){
					s.push(s.pop()/s.pop());
				}
				if(c.equals("*")){
					s.push(s.pop()*s.pop());
				}
			}
				
		}	
		return(s.pop());
	}
}