Midterm Exam Answers -- Winter 15

Part A.

 1. a. Use a "parse" method to convert a string to a numeric value.
 2. d. String.valueOf converts a numeric value to a string.  You can also use n + ""
       because whenever concatenation involves a string, the result is a string.
 3. a.
 4. c. This is the definition of an instance variable.
 5. a. r.nextDouble( ) is always a number between 0.0 and 1.0.
       Math.min(m, r.nextDouble( )) is always 0.0 because m starts out as 0.0 and is
       always smaller than the random number.
 6. d. The indices for the standard IO streams are 0 for stdin, 1 for stdout, and 2 for stderr.
 7. c or d. the statement  col.add = 5; should have been  col.add(5);
 8. b.
 9. d.
10. d.

Part B.

1. Since a.substring(i, i+1) returns the ith letter of a as a string,
   int h = Integer.parseInt(items.substring(i, i+1));  and
   int k = Integer.parseInt(letters.substring(i, i+1));
   pick out the ith digit of items and letters, respectively, converted to a digit.
   
     h     k    cities[h].charAt(k)   output
   =====+=====+=====================+================
     1  |  3  |         'v'         | "v"
     0  |  4  |         'a'         | "va"
     2  |  5  |         'l'         | "val"
     1  |  1  |         'e'         | "vale"
     1  |  2  |         'n'         | "valen"
     2  |  3  |         't'         | "valent"
     0  |  2  |         'i'         | "valenti"
     1  |  2  |         'n'         | "valentin"
     2  |  6  |         'e'         | "valentine"
     
Part C:

1. public static int findMaxIndex(int[ ] arr) {
       int maxVal = 0; maxIndex = 0;
       for(int i = 0; i < arr.length; i++) {
           if (arr[i] > maxVal) {
               maxVal = arr[i];
               maxIndex = i;
           }
       }
   }

   public static void main(String[ ] args) {
      int[ ] a = {5, 3, 1, 5, 9, 4, 2, 1}
      System.out.println(findMaxIndex(a);
   }
   
   // Output:
   3
   
2. public static String getMonthAbbrev(int month) {
      String[ ] abbrevs = {"JAN", "FEB", "MAR", "APR",
          "MAY", "JUN", "JUL", "AUG", "SEP", "OCT", "NOV", "DEC"};
      if (0 <= month && month <= 11) {
          return abbrevs[month];
      }
      else {
          return "Illegal month code.";
      }
   }
   
   public static void main(String[ ] args) {
       System.out.println(getMonthAbbrev(8));
       System.out.println(getMonthAbbrev(13));
       
   }
   
   // Output:
   SEP
   Illegal month code.
   
Part D:  See class notes.

Part E: Find the errors.  Corrections are marked with <--

==== Source code file Vehicle.java ==========================
// There are about 5 errors in this Vehicle class.  Correct them.
private class Vehicle {  <-- Change private to public.
    private String vin, color, driver;   <-- Delete , driver and add following line
    private Person driver;               <-- Add line
    public Vehicle(String theVin, String theColor, 
        Person theDriver) {
            vin = theVin;
            color = theColor;
            driver = theDriver;
    }
    Override   <-- Add @ before Override
    public String toString( ) {
        return String.format("VIN: %s Color: %s Driver: %d",  <-- change %s to %d.
            vin, color, driver.getName);   <-- Add ( ) after getName.
    }
    <-- Insert {  

==== Source code file Taxi.java =============================
     // There are about 5 errors in this Vehicle class. Correct them.
public class Taxi < Vehicle {   <-- Change < to extends.
    private String pickupLocation;
    private String dropoffLocation;
    private Person passenger;
    public void Taxi(String theVin, String theColor,  <-- delete void
        Person theDriver) {
        super(theVin, theColor, theDriver);
        pickupLocation = "";
        dropoffLocation = "";
        passenger = null;
    }
    public void pickup(Person thePassenger,    
        String theDropoffLocation)
        Person passenger = the_Passenger;   <-- delete Person
        dropoffLocation = theDropoffLocation;
    }

    @Override
    public String toString( ) {
        String passengerName = "";
        Person p = getPassenger( );
        if p != null {     <-- Add ( ) around p != null.
            passengerName = p.getName( );
        }
        else
        {
            passengerName = "No passenger";
        }
        return super.toString( ) + "\n" +
            String.format("Pickup Location: %s\n" +
                "Passenger Name: %s\n",
                "Dropoff Location: %s", pickupLocation,
                passengerName, dropoffLocation);
        }  <-- Delete
   } 
}    


==== Source code file Main.java =============================
// There are about 5 errors in this main class.  Correct them.
public class Main {
    public static String main(String args)  <-- Change 1st String to void, 
                                                insert [ ] after 2nd string
        Taxi t1 = new Taxi("abc34567", "yellow", 
            Person.new("Bruno", 'M', 45));   <-- Change Person.new to new Person.
        t1.setPickupLocation("Art Institute");
        t1.pickup(new Person("Julie", 'F', 29), 
            "Union Station");
        System.println(t1);  <-- Insert .out after System.
    }
}

2.    Write the source code for the getter getPickupLocation and the setter 
setPickupLocation for the pickupLocation instance variable in the Taxi class.  10 points.

public String getPickupLocation( ) {
    return pickupLocation;
}

public void setPickupLocation(String thePickupLocation) {
    pickUpLocation = thePickupLocation;
}

3.    Write a Junit test class that tests the getter getPickupLocation and the setter 
    setPickupLocation that you wrote in the preceding problem.  10 points.

import static org.junit.Assert.*;
import org.junit.Before;
import org.junit.Test;

public class JUnitTest {

    Taxi t;

    @Before
    public void setUp() {
        t = new Taxi("WEUR384293", "yellow");
    }

    @Test
    public void test() {

        assertEquals("", t.getPickupLocation( ));
        t.setPickupLocation("Art Institute");
        assertEquals("Art Institute", t.getPickupLocation( ));
    }
}


Part F: 

// main method:
import java.io.File;
import java.io.IOException;
public class Main {

    public static void main(String[] args) 
        throws IOException {
        
        File f = new File("test.txt");
        
        // Print false because file 
        // does not yet exist.
        System.out.println("can read?: " + f.canRead( ));
        
        // Print false because file 
        // does not yet exist.
        System.out.println("can write?: " + f.canWrite( ));

        // Print false because file 
        // does not yet exist.
        System.out.println("exists?: " + f.exists( ));
        
        // Create new file, then retest above methods.
        System.out.println(f.createNewFile( ));
        
        // Print true because now file exists. 
        System.out.println("can read?: " + f.canRead( ));
        
        // Print true because now file exists. 
        System.out.println("can write?: " + f.canWrite( ));

        // Print because now file exists. 
        System.out.println("exists?: " + f.exists( ));
    
        // Print name of file.
        System.out.println("File name: " + f.getName( ));

        // Print name of file.
        System.out.println("Absolute path: " + f.getAbsolutePath( ));

        // Print false because filename text.txt is not absolute.
        System.out.println("Is absolute?: " + f.isAbsolute( ));

        // Print false because file is not a directory.
        System.out.println("Is directory?: " + f.isDirectory( ));

        // Print 0 because file is empty.
        System.out.println("File length: " + f.length( ));
        
        // Create new filename for directory
        File g = new File("testdir");
        
        // Print true because directory is created.
        System.out.println("File name: " + g.mkdir( ));

        // Print false because file is a directory.
        System.out.println("Is directory?: " + g.isDirectory( ));
    }
}

// Output
can read?: true
can write?: true
exists?: true
true
can read?: true
can write?: true
exists?: true
File name: test.txt
Absolute path: C:\sjost\it313\java-workspace\TestFileMethods\test.txt
Is absolute?: false
Is directory?: false
File length: 0
File name: true
Is directory?: true