public static void main(String[] args) {

        String str ="ab";

        Context context = new Context(str);

        List<Expression> expressions = new ArrayList<Expression>();

        expressions.add(new AExpression());
        expressions.add(new BExpression());

        for(Expression expression:expressions){
            expression.interpret(context);
        }

        System.out.println(context.getOutPut());
    }