// file ExpressionTree.java
// Expression tree. The internal nodes are labelled with the
// characters '+', -', '*', and '/' and correspond to these operations.
// The leaves have label 'C' (for constant).  The leaves have their
// value in an int field value.

public class ExpressionTree extends BinaryTree<Character> {
     private int value;

// Constructor for leaf node
       public ExpressionTree (int v) {       
            setLabel(new Character('C'));
            value = v; 
           }
//
// Constructor for internal node
       public ExpressionTree(Character c, ExpressionTree l, ExpressionTree r) {
            setLabel(c);
            setLeft(l);
            setRight(r);
         }

// Get the left or right hand subtree, annd cast it as an ExpressionTree
       public ExpressionTree expLeft() {
             return  (ExpressionTree) getLeft(); 
           }

       public ExpressionTree expRight() {
             return  (ExpressionTree) getRight(); 
           }

// Evaluate a node
       public int evaluate() {
           switch (getLabel()) {
               case 'C': 
                 return value;
               case '+':
                 return expLeft().evaluate() + expRight().evaluate(); 
               case '-':
                 return expLeft().evaluate() - expRight().evaluate(); 
               case '*':
                 return expLeft().evaluate() * expRight().evaluate(); 
               case '/':
                 return expLeft().evaluate() / expRight().evaluate(); 
               default: return 0; // should never reach this case
             }
          }
        
        public void displayNode(int indent) {
              for (int i=0; i < indent; i++) System.out.print(" ");
              if (getLabel() == 'C') System.out.println(value);
               else  System.out.println(getLabel());
          }

        public String parenthesizedExp() {
            if (getLabel()=='C') return new Integer(value).toString();
            else return "(" + expLeft().parenthesizedExp() + " " + 
                              getLabel() + " " +
                              expRight().parenthesizedExp() + ")";
            }
}