// SimpleParens: make use of the a simple stack of chars
//    Check for matching parens
import java.util.*;
public class SimpleParens { 

   public static void main(String[] args) {
      Stack s = new Stack(); // create a stack
      GetData getData = new GetData(); // create input class
      // push non-blank chars.  Interested only in ()
      char ch = getData.getNextNonBlank();
      Character chWrap = new Character(ch); // must wrap char to push
      char stackCh;
      while (ch != 65535) { // as byte this is -1
         if (ch == '(') {
            chWrap = new Character(ch);
            s.push(chWrap);
         }
         else if (ch == ')') {
            if (s.empty()) error();
            chWrap = (Character)s.pop();
            stackCh = chWrap.charValue();
            if (stackCh != '(') error();
         }
         else error();
         ch = getData.getNextNonBlank();
      }
      if (!s.empty()) error();
      System.out.println("Balanced parens");
   }
   private static void error() {
      System.out.println("Error: unbalanced parens");
      System.exit(1);
   }
}

// GetData: fetch next char
import java.io.*;
public class GetData { 
   private Reader in; // internal file name for input stream
  
   // GetData: constructor  
   public GetData () { 
      in = new InputStreamReader(System.in);
   }

   // getNextChar: fetches next char
   private char getNextChar() {
      char ch = ' '; // = ' ' to keep compiler happy
      try {
         ch = (char)in.read();
      } catch (IOException e) {
         System.out.println("Exception reading character");
      }
      return ch;
   }

   // getNextNonBlank: fetch next non-whitespace char
   public char getNextNonBlank() {
      char ch = getNextChar();
      while (ch == ' ' || ch == '\n')
         ch = getNextChar();
      return ch;
   }
} 

% java SimpleParens
( ( ( ) ( () ) () ) () )
Balanced parens
% java SimpleParens
( ( ) ) )
Error: unbalanced parens
% java SimpleParens
( ( # ) )
Error: unbalanced parens
% java SimpleParens
( ( ( ) ) ( ) )
Balanced parens
% java SimpleParens
( ( ( ) ) ( )
Error: unbalanced parens