Little Java Exerices 2
More Practice the Composite and Interpreter Patterns

Set Up

Problems

1. Define a method boolean member(int i) for IntList that returns true if i appears as an element of this and returns false otherwise. Modify the main method to test the new method.

2. Extend the preceding program by adding a subclass OrdCons extending Cons as defined in Exercise 3 in Section II of Tutorial 2. The IntList class should include the member method plus all methods in IntList introduced in Tutorial 2, except append. Modify the main method to test all of the methods in the new class including those inherited from Cons.

3. Override the definition of the member method in OrdCons to exploit the fact that any IntList that is an instance of OrdCons is sorted. Write appropriate code in main to test the the overriden method.

4. Make a new copy of the file teachjava.org/2002/hw/01/IntList.java and convert each occurrence of the the type int in a method signature to the equivalent "boxed" type Integer. You will have to insert some "transfer" functions to make the code work. The intValue method of class Integer converts this to the equivalent int. The construction new Integer(i) converts an int to an equivalent Integer.

5. Redo exercise 1 for the revised IntList class.

6. A BooleanExpression is either:

   • a Const(c) where c is either true or false;
   • And(b1,b2) where b1, b2 are BooleanExpressions;
   • Or(b1,b2) where b1, b2 are BooleanExpressions;
   • Not(b1) where b1 is a BooleanExpression; or
   • Implies(b1,b2) where b1, b2 are BooleanExpressions.
   Define a BooleanExpression class representing the preceding data definition. The class should include appropriate constructors of for each concrete class and overriding definitions of the toString() method so that:
   • Const(c) prints as "c"
   • And(b1,b2) prints as "(^ B1 B2)" where B1, B2 are the toString() forms for b1, b2
   • Or(b1,b2) prints as "(| B1 B2)"
   • Not(b1) prints as "~B1"
   • Implies(b1,b2) prints as "(> B1 B2)
   In addition, the class should include the method Constant eval() that evaluates this. Write a test method to test the class thoroughly.

7. Modify the definition your preceding BooleanExpression program as follows.
   • Delete the definition of the eval method.
   • Add the extra alternative
     • Variable(s) where s is a string
     to the definition of the BooleanExpression type.
   • Represent this alternative by a new subclass Variable containing an appropriate constructor and overriding definition of the toString method.
   • Define a new class Environment to represent an Environment where an Environment is defined either as:
     • Empty; or
     • Cons(name,value,tail) where name is string, value is a boolean, and tail is an Environment.
     The new class should include an appropriate constructor, an overriding definition of toString(), and a method boolean lookup(String name) that finds the first Cons object in this with a name field matching the name parameter and returns the value of the matching Cons object.
   • Add a new method Constant eval(Environment env) to the BooleanExpression class that evaluates this given the variable bindings in env. If this mentions a variable name that is not bound in env, then eval should throw a an UnboundVariableException where the class UnboundVariableException extends RuntimeException.
   • As always write a test method to thoroughly test your program.

8. Extra credit: define the class UnboundVariableException so that it records the name of the unbound variable and use a

   try 
   ... 
   catch 
   

   construction in main to accommodate multiple test cases involving unbound variables.