CS 112 - Introduction to Computer Science II Homework #12

Due: At the beginning of class 36.

NOTE: This work is to be done in pairs.  I strongly recommend the practice of Pair Programming described simply here.  Although team members are permitted to divide work, each team member should be able to informally present all work of his/her teammate.

Binary File I/O

1. Double File Conversion: In this exercise you will implement DoubleFileConverter.java according to this specification.

Consider the following three ways a list of double may be written out to a file:

• text file, one printed double per line
• binary file, one binary double at a time
• binary file, one ArrayList<Double> written once

Your task is to demonstrate an ability to write out and read in a list of doubles in any of these formats.

2. Two-Bit Random Access File: In this exercise you will modify BitRandomAccessFile (described in class) to allow the random access reading and writing of unsigned two-bit values (0, 1, 2, 3) in a file with TwoBitRandomAccessFile according to this specification.

Note:

• You cannot rely on the presence of BitRandomAccessFile.java. You must create TwoBitRandomAccessFile to operate independently of BitRandomAccessFile.
• For your development and debugging, it is helpful to study Java bitwise operators and how to print a Java byte as a binary representation String.

Guidance for implementation: Start with a copy of BitRandomAccessFile.java and rename it to TwoBitRandomAccessFile. In this file, you'll need 4 mask values for binary two-bit ranges 0b11000000, 0b00110000, 0b00001100, and 0b00000011. You'll also use integer division and modulus with 4 rather than 8.

• Setting a 2-bit value (0-3):
  • Compute the byte index (pos / 4) and the two-bit index (pos % 4).
  • Seek the byte position and read the byte into a variable b.
  • Clear the 2-bit position in b you want to write your (0-3) value into by doing a bitwise AND (&) with the complement (~) of the mask for that two-bit index.
  • Left-shift (<<) the value you want to write according to its two-bit index, and bitwise OR (|) with the 2-bit cleared byte b to get the byte you want to write back with the new value in place.
  • Re-seek the byte position and write the new byte b.
• Getting a 2-bit value (0-3):
  • Compute the byte index (pos / 4) and the two-bit index (pos % 4).
  • Seek the byte position and read the byte into a variable b.
  • Clear all bits except the 2-bit position in b you want to read by doing a bitwise AND (&) with the mask for that two-bit index.
  • Right-shift (>>) the value you want to read all the way to the right-most two bits according to its bit position.
  • Because right-shifting promotes to a 32-bit representation and a left-most 1 will fill positions with the same when right-shifting, mask the final result with a bit-wise AND of your mask for the right-most position (& 3).
  • Return this value.

3. Traffic Lights Solver: In this exercise, you will implement an algorithm that uses your TwoBitRandomAccessFile to compute and store whether or not each possible state in a 3-by-4 Traffic Lights game is a winning or losing state. Beginning with this starter code (including eval method pseudocode) implement TrafficLightsSolver to this specification. 

NOTE: This is a computationally intensive task, so testing may take several minutes.  You may want to set COLS = 3 for your own testing phase.  For submission (after you've thoroughly tested!), be sure that COLS = 4 and that there is no extra printing beyond that which is supplied.  As before, any excess printing that fills the submission system with large amounts of output will result in a 1 point (5%) deduction.

Rubric: (20 points total)

• 9 points: DoubleFileConverter (1.5 points per correct method)
• 6 points: TwoBitRandomAccessFile:
  • .5 points per constructor (×4), clear, close
  • 1.5 points per correct set, get
• 5 points: TrafficLightsSolver:
  • 4 points: eval
  • 1 point: isGameOver