Last Updated: 2017-11-21 Tue 17:33

CSCI 1103 Lab11: Review

CODE DISTRIBUTION: lab11-code.zip

  • Download the code distribution every lab
  • See further setup instructions below

CHANGELOG:

1 Rationale

This lab does not introduce any additional new material and is intended mainly for review. Complete the previous lab on stacks if you have not done so already and submit it. Then proceed to the review problems to prepare for the upcoming exam.

There is no check-off for this lab. Instead, full credit will be given for submitting answers to the questions given below in the file QUESTIONS.txt. The deadline for submission is by the next lab. You do not need to complete all review problems to get full credit for the lab.

Associated Reading

The following material from Eck will be covered on Exam 2 though it builds on material prior to that in the course.

Week Dates Lecture Eck Book
7 10/16 Methods / Functions Ch 4
8 10/23 Basic Objects / Classes Ch 5
9 10/30 Classes with Methods Ch 5
10 11/06 Object-oriented Classes Ch 5
11 11/13 Simple Data Structures Ch 8.3.3, 7.4, 9.3

2 Download Lab Code and Setup

As in Lab01, download the code pack linked at the top of the page. Unzip this which will create a folder and create your files in that folder.

File State Notes
PARTNERS.txt Edit Fill in your name and the name of your partner in this text file
QUESTIONS.txt Edit Write your answers to review problems in this file and submit
Critter.java Provided/Edit Class for Review Problem 1
CritCompare.java Provided/Edit Class for Review Problem 1

3 Complete Lab10 on Stacks

If you have not completed work on the FixedStack and GrowableStack from lab10, do so before proceeding to review. Check-offs and submission on this lab will be allowed through the end of the day.

Importantly, make sure you understand how to make the GrowableStack appear to have an unlimited capacity by allocating larger arrays, copying elements, and referring to the new array as elements are push()'d in into it. Be able to draw pictures of how this process looks.

4 Review Problem 1: Critter Troubles

Consider the Critter class included with the lab code and answer questions about it. 

 1: // Represent a creature of some kind
 2: public class Critter{
 3:   private String kind;
 4:   private String eats;
 5:   private double ferocity;
 6: 
 7:   public Critter(String kind, double ferocity){
 8:     this.kind = kind;
 9:     ferocity = ferocity;
10:   }
11: 
12:   public String getEats(){
13:     return this.eats;
14:   }
15: 
16:   public void addToMenu(String kind){
17:     this.eats += kind + " ";
18:   }
19: 
20:   public static void encounter(Critter a, Critter b){
21:     if(a.ferocity > b.ferocity){
22:       System.out.printf("%s would beat %s\n",
23:                         a.kind,b.kind);
24:     }
25:     else if(a.ferocity < b.ferocity){
26:       System.out.printf("%s would beat %s\n",
27:                         b.kind,a.kind);
28:     }
29:     else{
30:       System.out.printf("%s and %s grab falafel together\n",
31:                         b.kind,a.kind);
32:       
33:     }
34:   }
35: }

4.1 Part A

Examine the constructor as it stands now. Draw a memory diagram of the following instance of the class (you do not need to include the picture in your submission but may have to draw one on an exam). 

public void main(){
  Critter hb = new Critter("Honey Badger",5.0);
  ...
}

Does anything look wrong about the picture compared to how objects are typically initialized?

4.2 Part B

In an interactive session, the following code is run which produces somewhat unexpected results. 

> Critter hb = new Critter("Honey Badger",5.0);
> hb.addToMenu("snakes")
> hb.getEats()
"null snakes"

Explain why the word null appears in the result of the getEats() method. Relate this to a problem in with the constructor about and describe fix in the constructor

4.3 Part C

An interactive session shows the following strange result. 

> Critter ra = new Critter("Rabbit",1.0);
> Critter fo = new Critter("Fox",3.0);
> Critter hb = new Critter("Honey Badger",5.0);
> Critter.encounter(fo, ra)
Rabbit and Fox grab falafel together             // Fox should beat Rabbit
> Critter.encounter(hb, ra)
Rabbit and Honey Badger grab falafel together    // Honey Badger should beat Rabbit
> Critter.encounter(hb, fo)
Fox and Honey Badger grab falafel together       // Honey Badger should beat Fox

The encounter() method appears to be broken. Identify a problem with the constructor which is causing this problems later with encounter(). Describe how to fix it.

4.4 Part D

Examine the encounter() method. It makes use of private variables of the Critter class like kind and ferocity. Compiling the Critter.java file appears to work fine as in 

> javac Critter.java
> ls Critter.class       // check for compiled class
Critter.class            // it is present

Compare to attempting to compile the separate class CritCompare.java that has the identical method in it: 

 1: public class CritCompare{
 2:   public static void encounter(Critter a, Critter b){
 3:     if(a.ferocity > b.ferocity){
 4:       System.out.printf("%s would beat %s\n",
 5:                         a.kind,b.kind);
 6:     }
 7:     else if(a.ferocity < b.ferocity){
 8:       System.out.printf("%s would beat %s\n",
 9:                         b.kind,a.kind);
10:     }
11:     else{
12:       System.out.printf("%s and %s grab falafel together\n",
13:                         b.kind,a.kind);
14:       
15:     }
16:   }
17: }

This leads to lots of errors: 

> javac CritCompare.java
CritCompare.java:3: error: ....
...
10 errors

Explain why compiling Critter.java works but CritCompare fails and the meaning of the private access modifier.

5 Review Problem 2: Portfolio Additions

5.1 Part A

Draw a memory diagram of the following interactive session of using the Portfolio class. 

> Portfolio barren = new Portfolio("Barren", 3);
> barren.deposit(200.00);
> barren.addStock("MSFT",10.00,"Microsoft");
> barren.addStock("AAPL",50.00,"Apple.");
> barren.buyShares("MSFT", 4);
> barren.buyShares("APPL", 2);
> barren.buyShares("GOOGL", 3);

5.2 Part B

Add a method to the Portfolio class with the following prototype. 

public class Portfolio{

  // Search the array of stocks for the given symbol and remove that
  // stock from the array by sellig off all shares of it. If any
  // shares exist, add the sale profit to the portfolio cash.  After
  // selling off all shares, eliminate the stock from the array by
  // shifting all remaining stocks back in the array and decreasing
  // the size. Return true if a stock is removed. If no stock with the
  // requested symbol exists, do not modify the portfolio and return
  // false.
  public boolean removeStock(String symbol){
    // YOUR CODE HERE
  }

5.3 Part C

Most actual stock portfolios change in value because the price of stocks is not fixed. Instead, stock prices fluctuate over time. To model this, consider the addition of the following method to the Portfolio class. 

public class Portfolio{

  // Search the array of stocks for the given symbol and change its
  // price to the given newPrice.  If a price is changed, return
  // true. If the requested symbol is not present, return false.
  public boolean updateStockPrice(String symbol, double newPrice){
    // YOUR CODE HERE
  }
  • Describe how one might implement this method in Portfolio perhaps giving code to do it.
  • You should encounter one major difficulty in your implementation of the updateStockPrice(). Describe this and an associated change that would be required in the Stock class.

6 Getting Credit for this Lab

There is no need to demonstrate / check-off your lab with staff. Discuss review problems with them to improve your understanding.

Full credit for the lab will be given for submitting your answers in QUESTIONS.txt to canvas.

On Canvas:

  • Click on the Assignments section
  • Click on the appropriate link for this lab
  • Scroll down to "Attach a File"
  • Click "Browse My Computer"
  • Select your QUESTIONS.txt file and press OK
Author: Chris Kauffman (kauffman@cs.gmu.edu)
Date: 2017-11-21 Tue 17:33