COS126

• Download PostfixL.java

/******************************************************************************
  * Name: COS 126 Staff
  * NetID: cos126
  * Precept: P00
  * 
  * Fall 15 Programming Exam 2, part 2
  * Description: Client class that simulates a stack machine to create
  * languages.
  * 
  * Started with code copied from Postfix.java in Lecture 12 slide 18:
  * http://www.cs.princeton.edu/courses/archive/fall15/cos126/lectures
  *  /CS.12.StacksQueues.pdf
  *  
  
*****************************************************************************/
public class PostfixL {
    public static void main(String[] args) 
    { 
        Stack<Language> stack = new Stack<Language>(); 
        while (!StdIn.isEmpty()) 
        { 
            String token = StdIn.readString(); 
            if (token.equals("UNION"))  
                stack.push(stack.pop().union(stack.pop())); 
            else if (token.equals("CONCATENATE")) {
                Language top = stack.pop();
                Language nextToTop = stack.pop();
                stack.push(nextToTop.concatenate(top));
            }
            else if (token.equals("CLOSURE")) {
                int n = StdIn.readInt();
                stack.push(stack.pop().closure(n)); 
            }
            else if (token.equals("PRINT")) {
                StdOut.println(stack.pop());
            }
            else {
                // new language formed from string
                Language newLang = new Language(token);
                stack.push(newLang); 
            }
        } 
    } 
}