import java.util.Stack;
import java.util.EmptyStackException;
import javax.swing.JOptionPane;
 
public class ParenChecker {
 
   private static final String OPEN = "([{";
 
   private static final String CLOSE = ")]}";
 
     public static boolean isBalanced(String expression) {
     Stack s = new Stack(); // Create an empty stack.
     boolean balanced = true;
     try {
       int index = 0;
       while (balanced && index < expression.length()) {
         char nextCh = expression.charAt(index);
         if (isOpen(nextCh)) {
           s.push(new Character(nextCh));
         }
         else if (isClose(nextCh)) {
           char topCh = ( (Character) s.pop()).charValue();
           balanced = OPEN.indexOf(topCh)
               == CLOSE.indexOf(nextCh);
         }
         index++;
       }
     }
     catch (EmptyStackException ex) {
       balanced = false;
     }
     return (balanced && s.empty());
   }
 
    private static boolean isOpen(char ch) {
     return OPEN.indexOf(ch) > -1;
   }
 
   private static boolean isClose(char ch) {
     return CLOSE.indexOf(ch) > -1;
   }
 
   public static void main(String args[]) {
 
     String expression = JOptionPane.showInputDialog(
         "Enter an expression containing parentheses");
     if (ParenChecker.isBalanced(expression)) {
       JOptionPane.showMessageDialog(null, expression
                                     + " is balanced");
     }
     else {
       JOptionPane.showMessageDialog(null, expression
                                     + " is not balanced");
     }
     System.exit(0);
   }
}