11. Simulations

What We Will Cover Reminders: Please silence all cell phones and pagers Sit at a computer station, start your computer, login and turn off your monitor When class is over, please shut down your computer. Remember that you lose any files not saved off the computer. Illuminations 11.1: Reviewing Ants 11.1.1: About Simulations 11.1.2: Setting up the Formicarium 11.1.3: Moving Towards an Object 11.1.4: Gaussian Distributions 11.1.5: Getting a Normally Distributed Random Number Exercise 11.1 11.1.6: Review 11.2: Adding Pheromones 11.2.1: Pheromones and the Search for Food 11.2.2: Drawing Pheromones 11.2.3: Dropping the Pheromones 11.2.4: Following the Trail 11.2.5: Path Forming Exercise 11.2 11.2.6: Review 11.3: Dialogs 11.3.1: Foxes and Rabbits 11.3.2: Java's GUI Libraries 11.3.3: User Dialogs 11.3.4: Dialog Arguments 11.3.5: Adding Dialogs to a Greenfoot Scenario 11.3.6: Project Dialog Exercise 11.3 11.3.7: Review Wrap Up Due Next: A8: Image Manipulation (4/25/12) A9: Project Proposal (5/2/12) Illuminations Questions from last week or the Reading? Midterm Questions? Has anyone NOT completed the second midterm yet? Midterm policy Grade calculation spreadsheet in Blackboard Tutoring resources How do you make a program with problems compile? Homework Questions? A8: Image Manipulation (4/25/12) ^ top 11.1: Reviewing Ants Learner Outcomes At the end of the lesson the student will be able to: Describe what is meant by the term "simulation" Write code to use the Random class of the Java API Write code to display a Gaussian distribution in two dimensions ^ top 11.1.1: About Simulations This week we get to explore an exciting topic: computer simulations A computer simulation is a program that imitates or models a particular system Simulations are used for many things, from training aircraft pilots to scientific modeling With simulations we can: Better understand the system we simulate Predict what will happen in the future These two capabilties make simulations a very powerful tool As an example, we worked with a simple physics simulation in lesson 7 (chapter 6) The simulation was too simple to accurately predict planteary motion very far into the future However, the simulation helped us to undersand how gravity interacts with objects in a planetary system Before we continue, lets review some key concepts from the chapter Concept Review Simulation: an imitation of some real thing or process. Computer simulation: a program that imitates or models a particular system. Pheromone: chemical signals that trigger a social response in members of the same species. Gaussian distribution: the normal distribution where values cluster around a mean value. Emergent behavior: the way complex behavior arises out of many simple interactions. Check Yourself Of the following, ________ is NOT an example of a simulation. a device that artifically re-creates aircraft flight a computer model of the solar system driving your car to school weather prediction True or false: a computer simulation is a simulation that runs on a computer. True or false: pheromones are chemicals used by some insects species to trigger behavior such as following a food trail. True or false: a Gaussian distribution is another term for normal distribution. True or false: it is possible for computer systems to have behaviors that are not directly traceable to specific objects, but rather to the interaction of objects. ^ top 11.1.2: Setting up the Formicarium A formicarium is an enclosed area used for studying ant colonies Some people may call this an ant f__m simulation However, we cannot use the word ant and the word farm next to each other because the term is trademarked by Uncle Milton Toys, Inc. Evidently, their lawyers send letters people who use the term "generically" (see here) One person who was harassed by the lawyers was Scott Adams, the creator of Dilbert He received threatening letters for using "the words" in a Dilbert comic strip To resolve the issue, he was forced to write a clarification Studing Ants Ants are particularly good at foraging for food Scientists study the behavior of ants and other insects to understand their successful strategies Finding good strategies can help solve engineering problems in human societies, like: Computer networks Routing cell phone signals Transmitting electricity efficiently Traffic systems Insects are somewhat machine-like and successful insect strategies can often be implemented on computers Ants Scenario The first simulation scenario we want to look at is Ants Lets download and install this scenario: Scenario file: ants-2b.zip. Save the file to a convenient location like the Desktop Start Greenfoot and open the scenario (Greenfoot unzips the file for us) Reviewing the Scenario At this point in the development, the ants wander around looking for food When an ant finds food, it brings the food back to its ant hill The Creature class contains the methods for ant movement The class contains a deltaX, deltaY pair used to calculate how far to move creatures It solves many of the problems of how to move creatures: randomWalk(): move in random directions and speeds headTowards(actorObj): move toward another Actor object walk(): change locations based on deltaX and deltaY We will look at movement methods in more detail in the next section Food Collection Efficiency As we run the scenario, look at how long it takes the ants to collect all the available food The search for food is completely random and the ants do not remember where they get food In the future we will look at how ants improve the efficiency of the food collection Check Yourself Two words commonly used for a formicarium are ________ ________. Studying ant behavior has applications in ________. routing computer networks transmitting electicity more efficiently improving traffic systems all of these True or false: the purpose of the Creature class is to contain common methods for creatures in the simulation. More information How ants find their way Animal Behavior: On Ant Navigation ^ top 11.1.3: Moving Towards an Object One problem we often run into in games and simulations is moving an actor towards another actor This scenario solves the problem in several ways: headTowards(target): adjust the walking direction towards a target actor walkAwayFromHome(): walk away from the home ant hill walkTowardsHome(): walk towards the home ant hill All the methods work in a similar way We will look at headTowards(target) since it is a more general method Moving Towards Another Actor To head towards another actor, we first get the (x, y) location of the target actor We then get (x, y) location of the object we want to move towards and subtract the two: deltaX = target.getX() - getX(); deltaY = target.getY() - getY(); This gives us the two components to calculate the direction of our movement vector We need to limit our movement to our maximum speed, for which we use if-statements like: if (deltaX > SPEED) { deltaX = SPEED; } if (deltaY > SPEED) { deltaY = SPEED; } After limiting the speed, we set our new location setLocation(getX() + deltaX, getY() + deltaY); Note that after we calculate the vector for moving towards an actor, it is easy to reverse direction and move away To move away, we simply subtract deltaX and deltaY from our current location Algorithm for Moving Towards Another Object Calculate the deltaX between this object and the target object Calculate the deltaY between this object and the target object Limit the deltaX so it does not exceed the maximum allowed speed Limit the deltaY so it does not exceed the maximum allowd speed Set the location of the object as (x + deltaX, y + deltaY) Methods headTowards(), capSpeed() and walk() of Creature public void headTowards(Actor target) { deltaX = capSpeed(target.getX() - getX()); deltaY = capSpeed(target.getY() - getY()); } private int capSpeed(int speed) { if (speed < -SPEED) return -SPEED; else if (speed > SPEED) return SPEED; else return speed; } public void walk() { setLocation(getX() + deltaX, getY() + deltaY); setRotation((int) (180 * Math.atan2(deltaY, deltaX) / Math.PI)); } Check Yourself True or false: deltaX and deltaY are the x- and y-components of the distance between two locations. To calculate deltaX, ________ the current location from the target location. To limit the length of a movement vector, we use an ________ statement with a test condition comparing the speed to a maximum speed. True or false: to move an actor you change its location. Enter the code to move an actor based on deltaX and deltaY. answer ^ top 11.1.4: Gaussian Distributions One of the objects we added to the scenario in our homework was Food One of the interesting problems we had to solve was making the piles of food look normal To randomly distribute food dots in the image, we first calculated random x and y coordinates, like: x = Greenfoot.getRandomNumber(image.getWidth()); y = Greenfoot.getRandomNumber(image.getHeight()); However, that made the piles of food look square as shown in Figure 9.3 of the textbook (see below) We can improve the distribution by using a Gaussian (or normal) distribution Distribution of Food Crumbs Uniform distribution Gaussian distribution Random Distributions Many random number generators produce a distribution that is uniform The chance of every possible number is the same A Gaussian random number generator produces a normal distribution An application like a dice game or card game needs a uniform distribution We want every roll of a die or draw of a card to have the same chance However, if we want to model dropping crumbs on the ground we need a normal distribution Crumbs dropped on the ground normally center around a central point Dropping crumbs follows the normal distribution's 68-95-99.7 rule where: About 68% of observations fall within 1 standard deviation of the mean About 95% of observations fall within 2 standard deviations of the mean About 99.7% of observations fall within 3 standard deviations of the mean We can see these standard deviations and percentages in the following diagram Normal Distribution Check Yourself Another term for a Gaussian distribution is __________ distribution. When we want random numbers to simulate rolling dice, we need a(n) __________ distribution. Besides dropping crumbs on the ground, what other common phenomena follow normal distributions? Age of populations Physical measurements like height and weight Test scores Time people spend playing video games To capture 99.7% of a normal population we need __________ standard deviations about the mean. ^ top 11.1.5: Getting a Normally Distributed Random Number To get numbers from a Gaussian distribution, we use the Random class from the Java API We construct an object from class Random in the usual way: Random randomizer = new Random(); After constructing an object, we can call any of its methods However, the method we are interested in is the nextGaussian() method nextGaussian(): returns a normally distributed double value with mean 0.0 and standard deviation 1.0. Getting a Normal Random Coordinate The nextGaussian() method returns a number between -infinity and +infinity However, 99.7% of the time the method will return a number between -3.0 and +3.0 We need to convert the random number into a positive integer within the size of the food image A good strategy is to add a shifting value to the number returned In this case, we could add the number 3 to the number returned 3 + random.nextGaussian() What range of numbers do we usually get now? Most of the time this will give us a positive number between 0 and 6 We then divide by 6 to get a number between 0 and 1 (3 + random.nextGaussian()) / 6 Now we need to scale the number to the size of the image (3 + random.nextGaussian()) / 6 * size The variable size is known as scaling the value To finish, we need to handle the 0.3% of the numbers we get outside the image size We can either limit the outliers to the image size or ignore them One solution is presented in the following method To call the method, we write code like: x = randomCoordinate(img.getWidth() - 1); y = randomCoordinate(img.getHeight() - 1); Method randomCoordinate() of Class Food private int randomCoordinate(int size) { int coord = (int) ((3 + randomizer.nextGaussian()) / 6 * size); if (coord < 0) { coord = 0; } if (coord > size) { coord = size; } return coord; } Check Yourself The Java API class we use to get a Gaussian distribution is named ________. The nextGaussian() method returns a negative number ________ the time. For the following code, ________ percent of the numbers output fall between 0.0 and 1.0. (3 + randomizer.nextGaussian()) / 6 For the above, ________ percent of numbers output will fall outside the range of 0.0 to 1.0. To scale a random number that is between 0.0 and 1.0, we ________ by the range we want. ^ top Exercise 11.1 In this exercise, we add a cycle counter to the simulation. Specifications Download the following file and save it in the scenario folder of Greenfoot. Scenario file: ants-2b.zip. Start Greenfoot and open the scenario. Greenfoot unzips the file for us. Open the AntWorld class and add an import statement for a List: import java.util.List; Also in the AntWorld class, add a private instance variable named ticks of type Counter. private Counter ticks = new Counter("Ticks:"); We will use this counter to measure food collection efficiency. In the constructor of AntWorld, add the ticks variable to the world that you created in the previous step. Compile the class and verify there are no errors. You should see the counter display on the screen at this step. Resolve any errors you find, getting help from a classmate or the instructor as needed. Add the following act() method to AntWorld: Compile and run your scenario to verify all the changes work well. If you have problems, ask a classmate or the instructor for help as needed. Run the scenario until all the food is gone. Write down the number of ticks counted until the food was collected. We will compare this measurement of food collection efficiency with other measurements. Save a copy of your scenario as we will be adding to it in the next exercise. Only submit the final scenario with all the lesson exercises completed, not the intermediate scenarios. As time permits, read the following sections and be prepared to answer the Check Yourself questions in the section: 11.1.6: Review. ^ top 11.1.6: Review Answer these questions to check your understanding. You can find more information by following the links after the question. Which of the following is NOT an example of a simulation? (11.1.1) Artificial re-creation of aircraft flight A computer model of the solar system Driving a car Weather prediction True or false: a computer simulation is a simulation that runs on a computer. (11.1.1) True or false: pheromones are chemicals used by some insects species to trigger behavior such as following a food trail. (11.1.1) True or false: a Gaussian distribution is another term for normal distribution. (11.1.1) True or false: it is possible for computer systems to have behaviors that are not directly traceable to specific objects, but rather to the interaction of objects. (11.1.1) Two words commonly used for a formicarium are ________ _______. (11.1.2) What is one good reason to study ant behavior? (11.1.2) What is the purpose of the Creature class? (11.1.2) What is the formula to calculate deltaX and deltaY? (11.1.3) How do we limit the length of a movement vector? (11.1.3) When we want random numbers to simulate rolling dice, we need a(n) ______________ distribution. (11.1.4) When we want to simulate dropping crumbs on the, we need a(n) ______________ distribution. (11.1.4) How many standard deviations about the mean do we need to capture 99.7% of a normal population? (11.1.4) What Java API class do we use to get a Gaussian distribution? (11.1.5) How often do we get a negative number from the nextGaussian() method? (11.1.5) For the following code, what percentage of the numbers output fall between 0.0 and 1.0? (11.1.5) (3 + randomizer.nextGaussian()) / 6 What percentage of numbers output from the above will fall outside the range of 0.0 and 1.0? (11.1.5) What technique do we use to scale a random number that is between 0.0 and 1.0 to a different range of values? (11.1.5) ^ top 11.2: Adding Pheromones Learner Outcomes At the end of the lesson the student will be able to: Implement pheromones in an ant colony simulation Describe a use of simulations in solving real life problems Discuss emergent behavior ^ top 11.2.1: Pheromones and the Search for Food Our current population of ants randomly search for food In nature, ants improve their food search through the use of pheromones Pheromone: chemical signals that trigger a social response in members of the same species. In this lesson we add pheromones to our scenario to see how this affects the ants search for food What we discover may give us ideas for solving other problems Dropping Phermones Each pheromone object represents a small drop of a chemical that ants leave on the ground An important property of pheromones is that each drop evaporates fairly quickly and then disappears Ants leave the pheremone drops when they return to the hill with a load of food When other ants smell the pheromones, they follow the trail of drops to the food By directing their search, food collection should be more efficient than random walking Starting Class Pheromone Pheromones start out strong and fade fairly quickly We will need a variable to save the intensity of the pheromone Also, we will display the pheromone in our simulation using an image We will have our program draw the pheromone image as a circle Once we have some idea what our class will do, we add class Pheromone to the simulation Variables for Class Pheromone private static final int MAX_INTENSITY = 180; private int intensity; Check Yourself Ants drop chemical signals known as __________ to tell other ants of a path to food True or false: pheromones evaporate and disappear over a short time. We can simulate the intensity of a pheromone using a(n) __________. ^ top 11.2.2: Drawing Pheromones Our ants are going to drop pheromones while returning to their home with food In our simulation, we will see the trail of pheromone drops as images We need to simulate phermones fading with time Our ants should find it harder to detect faded pheromone drops One way is to shrink the size of the image we display for the pheromone Ants are less likely to run into smaller images than larger images We can control the size of our pheromone image with our intensity variable The following is one way to write the updateImage() method Method updateImage() of Class Pheromone private void updateImage() { int size = intensity / 3 + 3; GreenfootImage img = new GreenfootImage(size, size); int alpha = intensity / 3; img.setColor(new Color(255, 255, 255, alpha)); img.fillOval(0, 0, size, size); setImage(img); } Transparency Notice how the transparency of the image (alpha) is controlled by the intensity int alpha = intensity / 3; img.setColor(new Color(255, 255, 255, alpha)); The lower alpha values gives us another way to see the fading of the pheromone Since we are working with colors we need to import the color library from the Java API: import java.awt.Color; When the pheromone gets created, we need to call the updateImage() method from the constructor After that we will use the act() method to control the fading effect Constructor of Class Pheromone public Pheromone() { intensity = MAX_INTENSITY; updateImage(); } Fading Over Time With the image controlled by intensity, we simply change the intensity in the act() method As you can see, we use the same recursive pattern we discussed in lesson 8.1.4 Use an instance variable to control the intensity and give the variable a starting value Change the value of the intensity in the act() method Test if the intensity has reached its goal with an if-statement Method act() of Class Pheromone public void act() { intensity--; if (intensity < 3) { getWorld().removeObject(this); } else { updateImage(); } } Manual Testing We can now manually test the Pheromone class with: new Pheromone() As the scenario runs, the Pheromone object fades away and disappears Check Yourself When first displayed, the size of the pheromone image is ________ pixels square. For the pheromone to disappear, the intensity must be less than ________. The alpha value of a pheromone is ________ when it disappears. What code would we add to updateImage() to show a small dot in the center of the image? img.setColor(Color.BLACK); img.fillOval(size / 2, size / 2, 2, 2); ^ top 11.2.3: Dropping the Pheromones Now that we have pheromones we need to get the ants to drop them Our ants should drop a pheromone only when carrying food as they move towards home Dropping a pheromone is a separate task so we should write a separate method We will need to call the new method from the act() method We can see the method below and we can test the scenario to see how it works Ant Method act() Calls dropPheromone() public void act() { if (carryingFood) { walkTowardsHome(); dropPheromone(); checkHome(); } else { searchForFood(); } } private void dropPheromone() { Pheromone ph = new Pheromone(); getWorld().addObject(ph, getX(), getY()); } Tesing Pheromone Drops When we test dropping the pheromone, we see that too much gets dropped into the world Ants cannot produce so much pheromone and do not need to either After placing a drop they need some time to produce more Thus we want to delay the production and only produce one pheromone drop over several cycles The textbook suggests 18 cycles as the correct amount private static final int MAX_PH_LEVEL = 18; We use a constant to avoid magic numbers and make the number of cycles easy to adjust (see lesson 6.1.4) What are the three steps to controlling timing over multiple scenario cycles? Add an instance variable to hold counting values and intialize the variable private int pheromoneLevel = 0; Change the value of the count in the dropPheromone() method pheromoneLevel++; Use an if-statement to test if the count has reached its goal if (pheromoneLevel >= MAX_PH_LEVEL) Since we want the pheromone level to repeat, we reset the pheromone level after every drop pheromoneLevel = 0; Updated Method dropPheromone() private void dropPheromone() { pheromoneLevel++; if (pheromoneLevel >= MAX_PH_LEVEL) { Pheromone ph = new Pheromone(); getWorld().addObject(ph, getX(), getY()); pheromoneLevel = 0; } } Testing the Improvement When we test the scenario now we see the drops are spread out However, our ants do not follow the pheromone trail yet We will add this capability in the next section Check Yourself True or false: separate tasks should be written in their own method. What are the three steps to controlling timing over multiple scenario cycles? Add an instance variable to hold counting values and intialize the variable private int pheromoneLevel = 0; Change the value of the count in the dropPheromone() method pheromoneLevel++; Use an if-statement to test if the count has reached its goal if (pheromoneLevel >= MAX_PH_LEVEL) We set pheromoneLevel = 0 after adding a pheromone to the world to ________ the count. ^ top 11.2.4: Following the Trail We need our ants to follow a pheromone trail If an ant smells a pheromone, it should first go the the center of the drop After reaching the center, the ant whould walk away from its home for some limited time Why should the ant walk away from home? Pheromone drops are made in approximately a straight line from the food to home. Because of how the path was created, the ant is following the path to the source If the ant does not shortly smell a new pheromone drop or find food, it should revert to random walking The textbook provides the logic for following the path in the form of psuedocode After working out the logic of a method in psuedocode we translate the method into program code Psuedocode for Following a Pheromone Trail if (we recently found a drop of pheromone) { walk away from home; } else if (we smell pheromone now) { walk toward the center of the pheromone drop; if (we are at the pheromone drop center) { note that we found pheromone; } } else { walk randomly; } check for food; The logic of searching for food belongs in our searchForFood() method However, we may need a few other helper methods to support searching for food Method searchForFood(): Psuedocode Implemented private void searchForFood() { if (foundLastPheromone > 0) { foundLastPheromone--; walkAwayFromHome(); } else if (smellPheromone()) { walkTowardsPheromone(); } else { randomWalk(); } checkFood(); } Notice that we need to control the timing of the search over multiple cycles Thus we add another instance variable to store the cycle counts private int foundLastPheromone = 0; Also, we use a constant for the number of cycles our ants move away from home: private static final int PH_TIME = 30; In addition, we implement the two helper methods Note the use of collision detection in the helper methods Method smellPheromone() public boolean smellPheromone() { Actor p = getOneIntersectingObject(Pheromone.class); return (p != null); } Method walkTowardsPheromone() public void walkTowardsPheromone() { Actor p = getOneIntersectingObject(Pheromone.class); if (p != null) { headTowards(p); walk(); if (p.getX() == getX() && p.getY() == getY()) { foundLastPheromone = PH_TIME; } } } Helper Methods Notice that the above methods help searchForFood() perform its task Separarate tasks should each have their own methods Sometimes, one method needs another to perform its task more easily These methods that help other methods are known as helper methods Check Yourself After working out the logic of a method in ________ we translate the method into program code The name of the variable used to control how long an ant walks away from home is ________. Why does walking away from home help an ant find the next pheromone drop or food? (answer) The method call in the above helper methods that checks for a collision is ________. When a method helps another method it is known as a ________ method. ^ top 11.2.5: Path Forming In nature, ants follow a phermone trail using their antennae to smell After following a path they are able to recognize and remember visual clues This makes traversing the path easier and faster than by using smell alone In the simulation, ants also follow the trail using the technique: Go to the center of the phernome drop Head away from home for a short time If another pheromene or food is not found then resume random walking Why does this work? Ants go directly home when they have food, dropping pheronomes along the way Thus, all pheromone drops are located directly between the food and home Also, the simulation has no obstacles that ants must go around With these simplifications, can we still learn about ants from our simulation? Ant Colony Optimization Algorithms It turns out that ant behavior was the inspiration for a set of optimization techniques in computer science Ant colony optimization algorithms are a part of computer science studies known as swarm intelligence Ant colony algorithms have produced an optimal solution to classic computer problems such as the Traveling Salesman Problem The traveling salesman problem is about how to find the shortest distance between the cities on the route of a traveling salesman Solutions to the problem has applications in business such as for delivery vehicles Emergent Behavior One interesting aspect of this simulation is that there is no code anywhere that talks about forming paths The programmed behavior of the individual ants is quite simple: If you have food go home while dropping pheromones; If you smell pheromones go away from home; Otherwise walk around randomly; However, together the ants display some sophisticated behavior They form stable paths, refreshing the pheromones as they evaporate Also, they efficiently transport food back to their ant hill This is known as emergent behavior The observed behavior is not programmed into an individual actor Instead, the behavior arises from the interaction of many simple actors Efficiency of Food Collection With pheromones added, the efficiency of the food collection increases We will explore how much the efficiency increases in the next exercise Check Yourself What aspects of the simulation regarding pheromone use are realistic and where have we made simplifications? True or false: ant behavior was the inspiration for solutions to computer problems that save businesses money on deliveries.) When complex behavior arises out of simple interactions, this is known as ________ behavior. How much improvement in food collection times do you think that adding pheromones produces, if any? More Information Ant colony optimization algorithms Swarm intelligence Traveling Salesman Problem Der Travelling Salesman und die Ameisen: Visualization of traveling salesman problem solved by ant systems. (Java Applet) ^ top Exercise 11.2 In this exercise, we test the impact of adding pheromones to the ants search for food. Specifications Start Greenfoot and open the scenario from the last exercise. If you are reinstalling the exercise, then download your AntWorld.java file from Blackboard and save it in the unzipped scenario folder. If you did not complete the last exercise, then you should do so now. Create a new subclass of actor named Pheromone, open the editor and copy this code to the new class. Compile the class after copying in the code and verify there are no errors. Resolve any errors you find, getting help from a classmate or the instructor as needed. Open the Ant class and add the following constants and instance variables: private static final int MAX_PH_LEVEL = 18; private int pheromoneLevel = 0; private static final int PH_TIME = 30; private int foundLastPheromone = 0; Compile the class after copying in the code and verify there are no errors. Resolve any errors you find, getting help from a classmate or the instructor as needed. In the Ant class and add the following methods: private void dropPheromone() { pheromoneLevel++; if (pheromoneLevel >= MAX_PH_LEVEL) { Pheromone ph = new Pheromone(); getWorld().addObject(ph, getX(), getY()); pheromoneLevel = 0; } } public boolean smellPheromone() { Actor p = getOneIntersectingObject(Pheromone.class); return (p != null); } public void walkTowardsPheromone() { Actor p = getOneIntersectingObject(Pheromone.class); if (p != null) { headTowards(p); walk(); if (p.getX() == getX() && p.getY() == getY()) { foundLastPheromone = PH_TIME; } } } Compile the class after copying in the code and verify there are no errors. Resolve any errors you find, getting help from a classmate or the instructor as needed. In the Ant class replace the act() method with the following: public void act() { if (carryingFood) { walkTowardsHome(); dropPheromone(); checkHome(); } else { searchForFood(); } } Compile the class after copying in the code and verify there are no errors. Resolve any errors you find, getting help from a classmate or the instructor as needed. In the Ant class replace the searchForFood() method with the following: private void searchForFood() { if (foundLastPheromone > 0) { foundLastPheromone--; walkAwayFromHome(); } else if (smellPheromone()) { walkTowardsPheromone(); } else { randomWalk(); } checkFood(); } Compile and run your scenario to verify all the changes work well. At this point your ants should drop phomones when they carry food and follow the pheromone trails when searching. If you have problems, ask a classmate or the instructor for help as needed. Run the scenario until all the food is gone. Write down the number of ticks counted until the food was collected. We will compare this measurement of food collection efficiency with other measurements. Assume that pollution has introduced a toxic substance into the ant's environment, such that the time between dropping pheromones is 4 times as long. Change the MAX_PH_LEVEL as follows and rerun the scenario until all the food is collected. Record the number of ticks counted for comparison with previous settings. private static final int MAX_PH_LEVEL = 18 * 4; Restore the MAX_PH_LEVEL setting and assume instead that another pollutant has decreased the ant's ability to remember when they smelled a pheromone. Instead of 30 steps they can only remember for 10 steps. Change the PH_TIME constant and rerun the scenario until all the food is collected. Record the number of ticks counted for comparison with previous settings. private static final int PH_TIME = 30 / 3; Save your completed scenario to upload to Blackboard as part of assignment 9. As time permits, read the following sections and be prepared to answer the Check Yourself questions in the section: 11.2.6: Review. ^ top 11.2.6: Review Answer these questions to check your understanding. You can find more information by following the links after the question. Ants drop chemical signals known as _____________ to tell other ants of a path to food (11.2.1) We can most easily simulate the intensity of a pheromone over time using: (11.2.1) an actor a chemical a variable a method Which of the following code statements add a small dot in the center of the GreenfootImage variable named img? (11.2.2) img.fillRect(size / 2, size / 2, 2, 2); img.drawLine(size / 2, size / 2, 2, 2); img.drawDot(size / 2, size / 2); img.setcolorAt(size / 2, size / 2); True or false: images can change size as a scenario runs. (11.2.2) To make a single object disappear from a scenario, use the following code in the class for the object: getWorld().removeObject(this); getWorld().removeLastObject(); getWorld().removeObjects(getObjects(this)); removeFromWorld(anObject); True or false: images can change transparency as a scenario runs. (11.2.2) Which of the following is NOT part of controlling timing of multiple scenario cycles? (11.2.3) Declare and initialize a counter instance variable. Change the value of the counter in the act() method. Use an if-statement to test if the counter has reached its goal. Call the setImage() method of the actor. Which of the following is a good reason to use a constant? (11.2.3) To document numbers To reduce code size To obfuscate numbers To use a static variable True of false: separate tasks should be written in their own method. (11.2.3) Methods that help other methods do their job are known as ___________ methods. (11.2.4) True or false: psuedocode can show us the logic of a method. (11.2.4) True or false: to follow a pheromone path an ant needs to walk away from home. (11.2.4) True or false: a simulation mimics real world behavior exactly. (11.2.5) True or false: ant behavior was the inspiration for solutions to computer problems that save businesses money on deliveries. (11.2.5) When complex behavior arises out of simple interactions, this is known as __________________ behavior. (11.2.5) ^ top 11.3: Dialogs Learner Outcomes At the end of the lesson the student will be able to: Describe what is meant by a GUI Collect user input in an input dialog box Confirm information with a confirmation dialog Show messages using a message dialog ^ top 11.3.1: Foxes and Rabbits The textbook provides a complete simulation known as foxes and rabbits The scenario attempts to predict the relationship in populations between an isolated population of foxes and rabbits Lets download and install this scenario: Scenario file: foxes-and-rabbits.zip. Save the file inside the Greenfoot scenarios folder. Start Greenfoot and open the scenario (Greenfoot unzips the file for us) Examining the Scenario The scenario is interesting and we looked at it during our homework However, the scenario has an extra feature not discussed in the textbook An extra window pops up and displays a graph The graph window is created by a Plotter object The Plotter object is constructed in the Field world in the usual way Looking at Plotter in more detail, we see class types like JFrame and JLabel JFrame and JLabel are part of the GUI somponent library that comes with Java Graphical User Interfaces GUI is an acronym for Graphical User Interface Graphical User Interface (GUI) -- pronounced "gooey" Graphical: not just text or characters but includes windows, menus, buttons, etc. User: person using the program via mouse, keyboard, etc. Interface: interaction with the program using visual controls, widgets, etc. Note that Greenfoot uses some standard GUI components -- where are they? We will take a closer look at some GUI components in the following sections Check Yourself GUI stands for G________ U________ I________. True or false: Java has a standard GUI libarary. What GUI components does Greenfoot itself use? ^ top 11.3.2: Java's GUI Libraries GUIs provide a graphical way to interact with a program The program presents information and users can enter information Users interact with GUI components using a mouse, keyboard or other input device Most modern applications use a GUI Typical graphical components include: Window: portion of screen providing an area for the other components Button: looks like a button that can be pressed Labels: Displays text or images in the window Text field: place where users can type values We can see the typical GUI components in the following image Example GUI Java's GUI Libraries GUIs are built from objects called components: Also called controls or widgets Java provides two sets of GUI components: AWT and Swing AWT (Abstract Window Toolkit) is the older set of components: Relies on the underlying visual components of the operating system AWT GUIs look different on every operating system Swing (like the dance) is the newer set of components: Extends AWT components and adds new capabilities Components draw their own visual shapes on the screen GUIs look about the same on every operating system The inheritance hierarchy below shows how Swing extends AWT Note that Swing components all start with the letter "J" As we can see, the GUI libraries are extensive with over 250 classes in Swing alone We will focus on only a small part in this lesson: JDialog Inheritance Hierarchy for GUI Components Check Yourself True or false: Java has two GUI libraries: AWT and Swing. True or false: Swing components all start with the letter "S" (for Swing). True or false: Swing components extend AWT components. ^ top 11.3.3: User Dialogs Sometimes we need a user to enter information into our scenario For example, we want their name to add to a high score list Other times we may want to provide them with a help window One easy way to solve these problems is to use dialog boxes Making a Dialog Dialogs provide a simple "popup" type of interaction with users JOptionPane provides several static methods for constructing dialogs Code for dialogs can be minimal For instance, to collect text input from a dialog: String inputString = JOptionPane.showInputDialog( "Enter your first name:"); Produces the following input dialog: Most dialogs are small windows with minimal options like the above Example Dialog Scenario Let's look at a simple scenario that demonstrates how to use dialogs: Scenario file: dialogs.zip. The scenario has three simple classes: DialogWorld: constructs the world and adds a Dialog object Telephone: displays an image, rings and starts the dialog sequence when clicked with a mouse Label: provides a simple way to display text in the scenario We will use three types of dialog boxes in sequence: showInputDialog: ask for name showConfirmDialog: verify entry showMessageDialog: display results These dialogs are created in the makeDialog() method of Dialog Method makeDialog() of Class Telephone public void makeDialog() { inputStr = JOptionPane.showInputDialog( "Hello, who is this?"); buttonNbr = JOptionPane.showConfirmDialog( null, "Are you sure?"); String msg = "First name: " + inputStr + "\nButton number: " + buttonNbr + "\nPress OK or Enter key to exit."; JOptionPane.showMessageDialog(null, msg); } Input Dialogs We use the showInputDialog() method of JOptionPane to get text input from users In the above example, we created the first dialog like this: inputStr = JOptionPane.showInputDialog( "Hello, who is this?"); Notice that we created the dialog in a single statement Confirmation Dialogs We use the showConfirmDialog() method of JOptionPane to confirm information The method will provide the user with three buttons: Yes, No and Cancel In the above example, we created the first dialog like this: buttonNbr = JOptionPane.showConfirmDialog( null, "Are you sure?"); Again, notice that we created the dialog in a single statement Message Dialogs We use the showMessageDialog() to show the user a message From the above example: String msg = "First name: " + inputStr + "\nButton number: " + buttonNbr + "\nPress OK or Enter key to exit."; JOptionPane.showMessageDialog(null, msg); Notice the "\n" character sequences in the above code These are known as newline characters and start a new line in text Dialogs let us use newline characters to layout text within our message string Commonly-Used Methods of JOptionPane Static Method Description showConfirmDialog Asks a confirming question, like yes/no/cancel and returns an int number corresponding to the button pressed. showInputDialog Prompts for user text input and returns a string containing the text entered by the user. showMessageDialog Displays a message and waits until the user presses a button in confirmation. Check Yourself True or false: dialog boxes can be constructed using class JOptionPane. True or false: dialogs can be created with a single statement. The type of data returned by the showInputDialog() method is ________. The type of data returned by the showConfirmDialog() method is ________. ^ top 11.3.4: Dialog Arguments Most methods of JOptionPane that create dialogs are overloaded to provide display options These options control dialog placement, messages and icons displayed, and title-bar wording Both showInputDialog() and showMessageDialog() accept the arguments listed in the table below For example, one method of showInputDialog() can accept four arguments: JOptionPane.showInputDialog(parentComponent, messageString, titleString, messageTypeInt); To display a different dialog without an input field: JOptionPane.showMessageDialog(parent, message); If the parent component is unknown, we use null for that argument JOptionPane.showMessageDialog(null, "Hello, world!"); Note that we cannot use our main Greenfoot window as a parent compoent Thus, we normally use null as the parent argument We can look up the exact usage for the various methods in the JOptionPane API documentation Commonly-Used Arguments in JOptionPane Methods Argument Description parentComponent An object representing the frame of the dialog box and controls its placement on the screen. If null is used, the dialog is centered on the screen. messageString A descriptive message displayed in the dialog box. titleString A title typically placed in the title bar above the dialog box. messageTypeInt Indicates the type of icon to display in the dialog box. Choosing one of the message types shown below will display the corresponding icon. icon Used if you want to display your own icon image rather than a built-in icon. Icons provided by JOptionPane Metal Windows Message Type Description ERROR_MESSAGE Displays an error icon. INFORMATION_MESSAGE Displays an information icon. WARNING_MESSAGE Displays an warning icon. QUESTION_MESSAGE Displays an question icon.     PLAIN_MESSAGE Does not display an icon. Check Yourself True or false: we can adjust the look of dialogs by changing arguments to the creation methods. True or false: we can set text in the title bar of a dialog. Enter a statement that creates an input dialog with the following options: A message that says, "Enter your name:". A title that says, "Winner". An icon that displays a question mark. answer More Information How to Make Dialogs ^ top 11.3.5: Adding Dialogs to a Greenfoot Scenario Let us look at how we can add dialogs to our scenario Step-by-Step Procedure for Adding Dialogs The first step is to decide which class will conduct the dialog In our example, the class is named Telephone The next step is to import JOptionPane: import javax.swing.JOptionPane; Set up a condition, usually in our act() method, that starts the dialog In our example, we used a mouse click: if (Greenfoot.mousePressed(this)) { // ... makeDialog(); // ... } Next, construct the sequence of dialog statements and save the user input we need public void makeDialog() { inputStr = JOptionPane.showInputDialog( "Hello, who is this?"); buttonNbr = JOptionPane.showConfirmDialog( null, "Are you sure?"); String msg = "First name: " + inputStr + "\nButton number: " + buttonNbr + "\nPress OK or Enter key to exit."; JOptionPane.showMessageDialog(null, msg); } Dialog Modality Note that dialogs are modal: they stop the scenario from running until the user finishes her input This is usually the behavior you want Why keep running a game while the user is looking at the instructions dialog? If we do not want modal behavior we will need a different approach We will look at more user input options later in the course Check Yourself Import the ________ API library when using dialogs. True or false: a scenario stops running while a dialog is displayed and resumes when the dialog is closed. The reason to use an if-statement in the act() method when creating a dialog is that the dialog ________ the scenario. ^ top 11.3.6: Project Dialog Over the next few weeks we will work on the final course project You have wide freedom in defining your project, though there are requirements to meet A project is a powerful way to develop a deeper understanding of programming You will work with many of the Java and Greenfoot features to develop your project At the end you will have created a program you can be proud of You will develop your project over four phases as shown below You will have about one week to complete each phase Project Phases Project proposal: define what your project is about Initial prototype: find out if your core concepts work User-testable prototype: get suggestions from other students Final project: the final version (at least for this course) ^ top Exercise 11.3 In this exercise, we explore the use of dialogs in Greenfoot. Specifications Download the following file and save it in the scenario folder of Greenfoot. Scenario file: dialogs.zip. Start Greenfoot and open the scenario. Greenfoot unzips the file for us. Open the Telephone class and locate the makeDialog() method. We will use this method to create our dialogs. Change the first dialog to ask the user to enter a name. Save the answer in the variable inputStr. Add another instance variable to the Telephone class, like: private String codeStr; Add a second input dialog statement asking the user to enter a code and save the answer in the above variable. For more information on input dialogs see section: 11.3.3: User Dialogs. Construct a message like the following: String msg = "Your name is " + inputStr + " and the code is " + codeStr + ". \nIs this correct?"; Show a dialog with the above message, and save the answer the user enters in the variable buttonNbr. For more information on confirmation dialogs see section: 11.3.3: User Dialogs. If the user pressed the No or Cancel button, then return from the method immediately. Hint: buttons are numbered from left to right with the first button on the left being number 0. If the user entered the code "42" (without the quotation marks), then show a message dialog saying, "The meaning of life." Otherwise, show a message dialog saying, "Wrong code. Try entering the number 42." For more information on message dialogs see section: 11.3.3: User Dialogs. Compile and run your scenario to verify all the changes work well. If you have problems, ask a classmate or the instructor for help as needed. Save your Telephone.java file to submit to Blackboard as part of assignment 9. As time permits, read the following sections and be prepared to answer the Check Yourself questions in the section: 11.3.7: Review. ^ top 11.3.7: Review Answer these questions to check your understanding. You can find more information by following the links after the question. GUI stands for G___________ U_________ I___________. (11.3.1) True or false: Java has a standard GUI libarary. (11.3.1) What are three components typically used in GUIs? (11.3.2) True or false: Java has two GUI libraries: AWT and Swing. (11.3.2) True or false: Swing components all start with the letter "S" (for Swing). (11.3.2) True or false: Swing components extend AWT components. (11.3.2) True or false: dialog boxes can be constructed using class JOptionPane. (11.3.3) What is the name of the method to create input dialogs? (11.3.3) What is the name of the method to create confirmation dialogs? (11.3.3) What is the name of the method to create message dialogs? (11.3.3) True or false: dialogs can be created with a single statement. (11.3.3) What type of data does the showInputDialog() method return? (11.3.3) What type of data does the showConfirmDialog() method return? (11.3.3) True or false: we can set text in the title bar of a dialog. (11.3.4) Write a statement that creates an input dialog with the following options: (11.3.4) A message that says, "Enter your name". A title that says, "Winner's name". An icon that displays a question mark. Which API library do you import when using dialogs? (11.3.5) True or false: a scenario stops running while a dialog is displayed and resumes when the dialog is closed. (11.3.5) ^ top Wrap Up Due Next: A8: Image Manipulation (4/25/12) A9: Project Proposal (5/2/12) When class is over, please shut down your computer You may complete unfinished lesson exercises at any time before the due date. ^ top Home | Blackboard | Schedule | Syllabus | Room Policies Help | FAQ's | HowTo's | Links Last Updated: April 29 2012 @00:45:34