CS302 Exam 2 Spring 2013 Reference Solution

Part I: Write a complete program

import java.util.Scanner;
public class EstimatePI {
    public static void main(String[] args) {
        Scanner scnr = new Scanner(System.in);
        System.out.print("Enter the number of darts: ");
        if ( !scnr.hasNextInt() ) errorMsg();
        int darts = scnr.nextInt(); // random throws per trial
        if ( darts < 1 ) errorMsg();

        // The simulation
        int side = 2; // the length of the side of a rectangle
        int radius = side/2; // the radius of the circle

        int inCircle = 0;
        for ( int p=0; p < darts; p++ ) {
            double x = Math.random()*side;
            double y = Math.random()*side;
            double d = Math.sqrt(Math.pow(x-radius,2)+
                Math.pow(y-radius,2));
            if ( d <= radius )
                inCircle++;
        }
        double pi_est = 4.0*(inCircle/(double)darts);
        System.out.print("Darts IN="+inCircle);
        System.out.println(" PI="+pi_est);
    }

    private static void errorMsg() {
        System.out.println("Must [be|enter] a positive integer!");
        System.exit(-1);
    }
}

Part II: Using pre-built classes

1. Write a code fragment...

int MAX_CHARS = 140;
for ( int i = 0; i < phrases.size(); i++ ) 
  if ( phrases.get(i).numChars() > MAX_CHARS ) 
     System.out.println( phrase.get(i).numChars() + " " + phrases.get(i) );

2. Write a class method ...

public static char getFirstUpperCaseLetter(String input) {
   char U = '-';
   boolean found = false;
   for ( int i=0; !found && i < input.length(); i++ ) {
      if ( input.charAt(i) >= 'A' && input.charAt(i) <= 'Z' ) {
         U = input.charAt(i);
         found = true;
      }
   }
   return U;
}

3. Write a class method ...

    public static boolean isPalindrome(String input) {
       boolean isP = true;
       for ( int i=0, j=input.length()-1; isP && i < j; i++, j-- ) 
          if ( input.charAt(i) != input.charAt(j) ) 
           isP = false;
       return isP;
    }

Part III: Write an instantiable class...

import java.util.ArrayList;
public class BackPack {

    private ArrayList<String> items;
    private String name;
    private boolean open;

    //REQUIRED PUBLIC MEMBERS (no additional public members may be added. 
     public BackPack(String name, boolean open) {
        this.name = name;
        this.open = open;
        this.items = new ArrayList<String>();
    }

    @Override
    public String toString() {
        String s = name + "'s backpack contains " + items.size() + " items, ";
        if ( open )
            return s + "and is open.";
        return s + "and is closed.";
    }

    public void addItem(String item) {  items.add(item);    }
    
    public void setOpen(boolean open) {     this.open = open;   }
    
    public boolean isOpen() { return open; }

    public int numItems() { return items.size(); }

    private String itemAt(int index) {
        if ( index >=0 && index < items.size() ) 
            return items.get(index);
        return null;
    }
} // end class BackPack


Part IV

1. Write a class method ...

    public static void rotate( int [] a, boolean right ) {
        int t;
        if ( right ) { 
            t = a[a.length-1];
            for ( int i=a.length-1; i > 0; i-- ) 
                a[i] = a[i-1];
            a[0] = t;
        } else { 
            t = a[0];
            for ( int i=0; i < a.length-1; i++ ) 
                a[i] = a[i+1];
            a[a.length-1] = t;
        }
    }
    
    
2. Write a code fragment ...

   int [][] rValues = new int[rLetters.length][];
   for ( i = 0; i < rValues.length; i++ ) {
       rValues[i] = new int[rLetters[i].length];
       for ( int j = 0; j < rValues[i].length; j++ ) {
           rValues[i][j] = rLetters[i][j] - ’A’;
       }
   }