SUNY Geneseo Department of Computer Science

Introduction to Lists

Previous Lecture

Misc

Amendments to student association constitution need your vote

• Knightweb -> "Answer a Survey" -> "SA Constitutional Amendment"

Updated versions of

• List.java
• RobotRoom.java

Exam 2 will be next Thursday (April 1)

• Not Tuesday like syllabus says
• Mainly lists, design and analysis of list algorithms
• Rules and format similar to first exam
• I'll find practice exam

Questions?

Saving lists - save in internal binary format

• Not text, not code
• Can restore into another list

Exceptions?

• Error signalling mechanism
• e.g.,

        double divide( x, y ) throws InvalidArgumentException
            if y != 0
                return x / y
            else
                throw new InvalidArgumentException()

• Abort execution of a block, yet communicate error to client
  • "Throw" = signalling error
  • "Catch" = receive signal
• Client:

        main() {
            try {
                double a = divide( x, 0.0 );
                print a
            }
            catch ( InvalidArgumentException e ) {
                print "I'm a fool! y = 0"
                System.out.println( e );
            }
            catch ( Exception e ) {
                System.out.println( "D'Oh!" );
            }
        }

• Exception classes:

• You can make your own exceptions

        class MyException extends Exception {
            public MyException( String desc ) {
                super( desc );
            }
        }
        ...
        throw new MyException( "User Error" );

Reading files:

• Default directory
• CodeWarrior: default = project directory

Lists

Section 11.1 through Section 11.3.1

• Examples of lists, basic idea of what one is
• Importance to CS
• Elements
• Manipulating lists
  • Adding new elements
  • Deleting elements
  • Combining lists
• Structure of lists
  • Small lists within large ones
  • Empty lists
  • Recursive!
  • List =
    • Object (head) followed by List (tail)
    • or Empty
  • Second element is head of the tail
• Actual list operations
  • Constructors
  • Other messages for lists
  • Changes to contents happen by deleting and then adding
  • addItem
  • removeItem
  • isEmpty
  • getAndRemove
  • getFirst
  • getRest

Example list algorithms

• Get second item:

        // In a subclass of List:
        Object second() {
            return this.getRest().getFirst();
        }

Next

Continue looking at list algorithms

Mini-Assignment

• Delete all occurrences of x from a list

        // In some subclass of List...
        public void delete( Object x )
            ...
        // Postcondition: List contains no items equal to x.

• See Section 11.3.2 for more examples

Next Lecture