More Practice with the Composite and Interpreter Patterns
¥In DrJava, open the file IntList.java.  We want to convert IntList.java to a program List.java that implements heterogeneous lists (lists that can hold arbitrary objects, not just elements of a particular type).  The element type in the program List.java must be Object.  Otherwise the code is unchanged.

¥Rewrite the concat and rev methods for heterogeneous lists.   Test your code on some lists of Integer.