// file Sum.java

public class Sum extends ExpTree {

   public Sum (ExpTree[] c) {
       super(c);
     }

   public Object evaluate() {
       int sum = 0;
       for (int i=0; i<getChildren().length; i++) 
          sum = sum + (int) getChildren()[i].evaluate();
       return (Integer) sum;
     }

   public String display() {
       String s = "(" + getChildren()[0].display();
       for (int i=1; i<getChildren().length; i++) 
          s = s + " + " + getChildren()[i].display();
       return s + ")";
     }
}