Test 1 CompSci 6 Fall 2009

Problem 1

A1. [2] A class represents an object in an abstract way, specifying
the common attributes of all objects of a specific kind. An
object is a specific instantiation of a class whose attributes have
specific values.

A2. [2] A constructor is a method that is called only when an object is
  constructed. It should initialize all instance variables to a
reasonable state so that any method can be called safely.

B. [5]
public boolean majority(boolean a, boolean b, boolean c)
{ 
  return a&b || a && c || b && c;
}

C. [2] Change return x to return x - 1

D. [3] "H. Brodhead, Richard"

Problem 2

A. [8]
int[] numbers;
int max;
in maxCount = 0;

max = Integer.MIN_VALUE;
for (int k=0; k < numbers.length; k+=1)
  if (numbers[k] > max)
    max = numbers[k];

for (int elem: numbers)
  if (elem == max)
    maxCount += 1;

B1. [3] For the first loop: max is the largest value of the first k elements

B2. [2] {3,8,8,2,4,4,1,7}

B3. [2] {3,8,8,3,2,4,1,7}

B4. [3] After each iteration of the loop, the following is true

    numbers[0...k-1] == unknown
    numbers[k-1...index-1] == either max or other
    numbers[index...numbers.length-1] == in final order with no maxes

B5. [2] {8,8,8,3,2,4,1,7}

Problem 3

Part A [5]
public int weightToOz(String weight)
{
  int pos = weight.indexOf(" ");
  int pos2 = weight.indexOf(" ", pos+1);
  int pos3 = weight.indexOf(" ", pos2+1);
  int lbs = Integer.parseInt(weight.substring(0,pos));
  int oz = Integer.parseInt(weight.substring(pos2+1, pos3));
  return 1bs * 16  + oz;
}

Part A Alternate Soln

public int weightToOz(String weight)
{
  int pos = weight.indexOf(" ");
  int posb = weight.indexOf("b");
  int poso = weight.indexOf("o");
  int lbs = Integer.parseInt(weight.substring(0,pos));
  int oz = Integer.parseInt(weight.substring(posb+2, poso-1));
  return 1bs * 16  + oz;
}

Part A Alternate2 Soln

public int weightToOz(String weight)
{
  // convert a String into a stream
  Scanner stringStream = new Scanner(weight);
  int lbs = Integer.parseInt(stringStream.next());
  stringStream.next(); // ignore "lbs"
  int oz = Integer.parseInt(stringStream.next());
  return 1bs * 16  + oz;
}

Part B [3]

public String ozToWeight(int n)
{
    int lbs = n/16;
    int oz = n%16;
    return  lbs + " lb " + oz + " oz";
}

Part C [7] 

public String[] readWClasses(Scanner input)
{

   int number = input.nextInt();
   String line = input.nextLine();   // get rest of line

   String [] answer = new String [number];

   for (int k=0; k<answer.length; k++)
   {
       line = input.nextLine(); 
       answer[k] = line.substr(line.indexOf(" ")+1);
   }
   return answer;
}

Part C Alternate Solution

public String[] readWClasses(Scanner input)
{

   int number = input.nextInt();

   String [] answer = new String [number];
   String lb, oz, weightclass;
   int lbnum, oznum;

   for (int k=0; k<answer.length; k++)
   {
       weightclass = input.next();
       lbnum = input.nextInt();
       lb = input.next();
       oznum = input.nextInt();
       oz = input.next();
       answer[k] = ozToWeight(lbnum * 16 + oznum);
   }
   return answer;
}

Part D [9]

public String nextWClass(String weight, String[] classes)
{
   int [] ounces = new int[classes.length];
   for (int k = 0; k < classes.length; k++)
   {
        ounces[k] = weightToOz(classes[k]);
   }

   Arrays.sort(ounces);
   int w = weightToOz(weight);
   for (int k=0; k< ounces.length; k++)
   {
        if (ounces[k] >= w)
        {
            return ozToWeight(ounces[k]);
        }
   }
   return "Heavyweight";

}

Problem 4

Note: Almost everyone assumed that BouncingBall's instance variables were
public or protected, as we do below.

import java.awt.Dimension;
import java.awt.Point;
import java.util.Random;

public class ColorfulBall extends BouncingBall
{
    public ColorfulBall(Point center, Point velocity)
    {
        super(center, velocity, null);
        Random gen = new Random();
        myColor = new Color(gen.nextInt(256),gen.nextInt(256),
                gen.nextInt(256));
     }
    
    public void move(Dimension bounds)
    {
        super.move(bounds);
        if (myCenter.x < RADIUS || myCenter.x > bounds.width-RADIUS ||
                myCenter.y < RADIUS || myCenter.y > bounds.height-RADIUS)
            // shift colors
            myColor = new Color(myColor.getBlue(), myColor.getRed(),
                    myColor.getGreen());
    }
    
    
}