//Overklasse af udtrykstræer med abstrakte metoder

class TestExpressionTree
{    public static void main( String [ ] args )
     { ExpressionTree exp  =
        new PlusTree ( new NumberTree(1),
                       new TimesTree( new NumberTree(2),
                                      new NumberTree(3)));
       exp.printStackCode();
       System.out.println();
       exp.printExpression();
       System.out.println();
       exp.printLispCode();
       System.out.println();}
}