Cat Simulator 2015

I worked together with my friend Tim to make a 'cat simulator' of sorts in Java. After naming your virtual cat, you can use text commands to pet it, give it things to play with / eat, or watch it interact with things you've given it. Here's an example run of the program:

You got a new pet cat! What do you want to name him?

Tom

You named him Tom.

What do you want to do?

(pet, give, watch, exit)

give

What item is it?

paper ball

Is it edible?

no

Tom plays idly with the paper ball.

(pet, give, watch, exit)

give

What item is it?

catnip

Is it edible?

yes

Tom stares at the catnip.

(pet, give, watch, exit)

watch

Tom eats the catnip. Viciously.

(pet, give, watch, exit)

watch

Tom meows.

(pet, give, watch, exit)

pet

You pet Tom and he purrs softly.

(pet, give, watch, exit)

pet

You pet Tom the wrong way, and he scratches you!

(pet, give, watch, exit)

The program is split into three .java files and three separate classes; a main class, a cat class, and an Object class. The main class handles command inputs and stores objects, the cat class decides what it wants to do with with the objects it's given, and the Object class stores information about each object.

The project code can be viewed in this Eclipse project.

Chapter 3

In experimenting with the Dog program example, I learned that Java reads all the class definitions (variables, constructors, methods, etc.) before executing public static void main (String[] args). This means you can have the main program inside a class, and that the program will start with one copy of that particular class. This makes me wonder if you could refer to itself in an array.

class Dog {
   public String name = "Ben";
   public static void main (String[] args) {
      Dog[] myDogs = new Dog[2];
      myDogs[0] = new Dog("Bob");
      myDogs[1] = this;
      int x = 0;
      while (x < myDogs.length) {
         System.out.println(myDogs[x].name); // Would this print "Bob" and then "Ben"?
      }
   }
   public Dog(String newnname) {
      this.name = newname;
   }
}

     

Chapter 2

In the second chapter of Headfirst java, I learned about subclasses and superclasses, and how subclasses can override superclass methods. For example, if we have a superclass called Shape, we can have subclasses Square and Triangle. The subclasses can have their own unique variables and classes, while preserving any of Shape's methods assuming they haven't been overridden.

Chapter 1 findings

In the first chapter of Headfirst Java, the two biggest things I learned about are casts and declaring arrays. Casts allow you to change numbers from one data type to another, such as from Float to Int.
Example:

float x = 32.25f;
if ((int) x == 32) {
     System.out.println("This will print because 32.25 rounds to 32.")
}
if (x==32) {
     System.out.println("This won't print because x is still 32.25.")
}

Arrays in Java are created somewhat differently than other languages- You have to tell the code you want an array after the primitive type. This means the array will only accept one type of data (String, integer, etc).

String[] animals = {"cats", "dogs", "pigs"}
int[] numbers = {1, 30, 25, 22.5} // This will throw an error, since 22.5 is a float in an integer array.

Beersong

So today I fixed a program that prints the words to the Beer Song, AKA 99 Bottles of  Beer.
Original code:

public class BeerSong {
    public static void main(String[] args) {
        int beernum = 99;
        String word = "bottles";
        
        while (beernum>0) {

            if (beernum==1) {
                word = "bottle";
            }

            System.out.println(beernum + " " + word + " of beer on the wall");
            System.out.println(beernum + " " + word + " of beer");
            System.out.println("Take one down");
            System.out.println("Pass it around");
            
            beernum = beernum - 1;

            if (beernum > 0) {
                System.out.println(beernum + " " + word + " of beer on the wall");
            } else {
                System.out.println("No more bottles of beer on the wall");
            }
        }
    }
}

This works well, except towards the end it prints "Pass it around, 1 bottles of beer on the wall" because the variable "word" is updated at the beginning of the loop rather than after the beer count changes.

public class BeerSong {
    public static void main(String[] args) {
        int beernum = 99;
        String word = "bottles";
        
        while (beernum>0) {
            System.out.println(beernum + " " + word + " of beer on the wall");
            System.out.println(beernum + " " + word + " of beer");
            System.out.println("Take one down");
            System.out.println("Pass it around");
            
            beernum = beernum - 1;
            if (beernum==1) {
                word = "bottle";
            }
            if (beernum!=0) {
                System.out.println(beernum + " " + word + " of beer on the wall");
            } else {
                System.out.println("No more bottles of beer on the wall");
            }
        }
    }
}

1.3.8 Activity response: While loops

Here I made a guessing game where you have to guess a number between 1 and 20 inclusive. It tells you if you guessed too high or too low, and even if you guessed a number outside of 1-20.

import random
def goguess():
    maxval = 20
    minval = 1
    target = random.randint(minval, maxval)
    print("I have a number between " + str(minval) + " and " + str(maxval) + ".")
    guess = int(raw_input("Guess: ")) #We put our first guess here because we check
    count = 1                         #the guess at the beginning of the while loop.
    while (not (guess == target)): #the while loop ends when you guess the number.
        if (guess <= maxval and guess >= minval):
            if (guess < target):
                print(str(guess) + " is too low.")
            else:
                print(str(guess) + " is too high.") # Tells if the guess is high or low.
            count += 1 #adds 1  to the count... count.
        else:
            if guess > maxval:    #Remind them if they guess outside the range.
                print(str(guess) + "is higher than " + str(maxval) + ".")
            else:
                print(str(guess) + "is lower than " + str(minval) + ".")
        guess = int(raw_input("Guess: "))
    print("You got it! The number was " + str(target) + ", and you guessed it in " + str(count) + " turns.") #This prints when the 'while' loop ends.

Conclusion question answers:

Q1: If you change between 1 and 20 from the previous program to between 1 and 6000, how many guesses will you need to guarantee that you have the right answer? Explain.

A1: To figure out how many guesses you need, you need find the first power of two above the maximum number. For example, guessing a number in a range 1-7 inclusive would take only three guesses.
2^guesses > max
2^3   = 8       > 7       --3 guesses for a range 1-7
2^5   = 32     > 20     --5 guesses for a range 1-20
2^13 = 8192 > 6000 --13 guesses for a range 1-6000.


Q2: Explain the difference between a while loop and a for loop.

A1: A "while" loop repeats constantly until a condition is met, whereas a "for" loop iterates through a list of values. In some languages like java you could use them interchangeably, but it's generally easier and faster to use whichever one makes more sense for the situation.

1.3.7 Activity response: For loops

On this assignment I only needed to do two of these three, but I went ahead and did all of them.

The first function, hangman_display(), will return the 'secret' string with letters that aren't in 'guessed' hidden or crossed out, much like in Hangman.
ex: hangman_display("aeiou", "hello world") -> "-e--o -o---"

The second, matches(), counts how many items between the two lists match, assuming neither list has duplicate items.
ex: matches([1,2,3], [2,3,4]) -> 2

The last function, report(), functions like the game Mastermind, returning how many items are the same in value and position, and how many items are in both lists but in different positions.
ex: report([a, b, c, d], [a, c, b, e]) -> [1, 2]

def hangman_display(guessed, secret):
    ret = ""
    for i in secret:
        x = 0
        for j in guessed:
            if i.lower() in j.lower():
                x = 1
        if x == 1 or (i in " !,.?"):
            ret = ret + i
        else:
            ret = ret + "-"
    return ret


def matches(tickets, winners):
    ret = 0
    for i in tickets:
        x=0
        for j in winners:
            if i==j:
                x = 1
        if x==1:
            ret += 1
    return ret


def report(guess, secret):
    ret = [0, 0]
    used = []
    for i in range(len(secret)):
        if secret[i]==guess[i]:
            used.append(i)
            ret[0] += 1
    for i in range(len(secret)):
        for j in range(len(guess)):
            if (not(j in used or i in used)) and secret[i]==guess[j]:
                ret[1] += 1
                used.append(j)
    return ret

Conclusion question answers:

1. This practice, known as "loop unrolling", is actually used in some cases to speed up program execution at the cost of increasing the program size. Using unrolled loops during development is tedious, boring and just plain inefficient- it'd be a royal pain to change an unrolled version of "for i in range(10):" to "for i in range(1000):", and even more painful to change anything inside said loop.
2. A grocery store computer might iterate over a list of items in stock.
3. Both iteration and data analysis deal with large amounts of data. Iteration reads from and/or changes information about each item, whereas data analysis only reads from them to get statistics.