space wars

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity

Let us create a small scenario in Greenfoot using what we have reviewed.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity We will create a new instance of the World class and name it Space. Right mouse click on World and select New subclass, name the new class Space, In this scenario we will not use a background image for the world.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity Now we have our world created let us look at the code editor and the Space constructor.

super(600,400,1);Construct a board(world) 600 x 400 pixels with a pixel size of 1x1

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity A world will be empty unless we add some Actors to it. We will create 3 Actor classes and assign an image to them.

Right mouse click on Actor and select New subclass, name the new classes Alien, Rocket and Shot and assign an image from the gallery, robot, rocket and beeper which are all in the Gallery.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity Now we have to rotate the images for both the Alien and the Rocket.

Right mouse click on the Alien actor and select Set Image, Select theimage from the Scenario images box, click settings and select Edit

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity The image will open up in paint, rotate the image right 90 degrees from the Rotate drop down.

Now do the same for Rocket only rotate it to an upright position left 90 degrees.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity Now we have created the Actors we can add instances of them to the World.

There are 3 ways to add instances of our Actor classes to the world.

Manually while the Scenario is running.Automatically When constructing the World.Automatically while the Scenario is running.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity Manually while the Scenario is running.

Compile and Run your scenario. Right mouse click onOne of the classes and select new then click where you want to place them on the world.

Add one instance of Rocket and two instances of Alien to your world.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity Manually while the Scenario is running.

Positives : Encourages users to add own instances where they want them.

Negatives : After each compilation and placed instances will be removed and world refreshed to blank.

Users will have the ability to add instances at any time no matter which method of adding instances is used.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity 2.Automatically When constructing the World.

Open the code editor of the Space class and add the followingcode :

addObject(new Rocket(),300,340);

Compile and run your scenario, you should now automatically have two an instance of Rocket positioned bottom centre of the world. We will cover Automatically while the Scenario is running later .

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity Now we have a Rocket let us make it move. We will use the left and right arrow keys to move the Rocket along the bottom of the world. To do this we will use the Greenfoot.isKeyDown() method. In the Act method of the Rocket enter the following code :

if (Greenfoot.isKeyDown("left")) { setLocation(getX()-5,getY()); }if (Greenfoot.isKeyDown("right")) { setLocation(getX()+5,getY()); }

Compile and run your scenario, the Rocket should now move left and right using the arrow keys.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity What use is having a space Rocket if it cant shoot anything that gets in its way? Let us add a way for the rocket to shoot a shot Actor.

In the Act method of the Rocket enter the following code after our left and right controls :

if (Greenfoot.isKeyDown("space")) { getWorld().addObject(new Shot(), getX(), getY()); }

Compile and run your scenario, the Rocket should now move left and right using the arrow keys and a shot should appear when space is pressed.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity Notice our shot just stays in the same place? Let us give the shot some movement.

In the Act method of the Shot Actor enter the following code :

if (getY() > 0) { setLocation(getX(), getY() -5); }Compile and run your scenario, shot should appear when space is pressed and move to the top of the world.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity Notice our shot just stays at the top of the screen? Let us remove the shot once it goes out of our world.

In the Act method of the Shot Actor edit the previous if statement to include the following code as an else

if (getY() > 0) { setLocation(getX(), getY() -5); }else { getWorld().removeObject(this);}Compile and run your scenario, shot should appear when space is pressed and move to the top of the world where it is removed.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity Let us now make it a little less easier to shoot all of those shots off, we will limit the shots to a short time delay in between.

Outwith the Act method of the Rocket Actor enter the following code To create a variable we can use to control the timing of shots.

private int shotTimer = 0;

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity Now edit the code to create a shot to the following :

if (shotTimer > 0) { shotTimer = shotTimer - 1; } else if (Greenfoot.isKeyDown("space")) { getWorld().addObject(new Shot(), getX(), getY()); shotTimer = 50; }

Compile and run your scenario, now the shot should not appear every time space is pressed but at a slower interval.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity Now we can shoot all we need is something to shoot at, how about one of those Alien actors we created earlier?

Open the code editor of the Space class and add the followingCode to the world constructor :

addObject(new Alien(),30,30);

Compile and run your scenario an Alien should have appeared and we can shoot right at it but nothing happens when we hit it.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity When we hit an Alien we need to remove both the alien and the aimed shot from the world. We will edit the code in the Act method of our Shot class to the following code :if (getY() > 0) { setLocation(getX(), getY() 5 ); Actor hit = getOneIntersectingObject(Alien.class); if (hit != null) { getWorld().removeObject(hit); getWorld().removeObject(this); } } else { getWorld().removeObject(this); }

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity One Alien is easy to hit, let us add some more.

Open the code editor of the Space class and edit the code to place the Alien instance to the following :

for(int i =1; i

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity Stationary Aliens are too easy to hit, let us give them some movement.

Open the code editor of the Alien class and edit the Act method to the following :

setLocation(getX(), getY()+1);

Compile and run your scenario those Aliens should be moving towards earth now.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity Now the Aliens are too fast to hit before they reach earth, let us give them a little less movement.

Open the code editor of the Alien class and edit the Act method to the following :

if (Greenfoot.getRandomNumber(4) == 2) { setLocation(getX(), getY()+2);}

Compile and run your scenario those Aliens shoot be moving towards earth a little faster now.

Greenfoot Activity Finally, let us add a Label class to keep track of our score.Create a new sub-class of Actor, give it the name Label, and leave the image empty.Open the code editor for the new class, and add a class-level attribute to keep track of the score:private int score;Create a constructor to initialise the score to 0 and use setImage() method to display the score variable on screen public Label() { score=0; setImage(new GreenfootImage("Score: "+ score, 30,Color.black, Color.white)); }

Greenfoot Activity Next, we need to add a method, to update the score.Add the following code below the existing act() method of the Label class:public void updateScore(int amount){ score+=amount; setImage(new GreenfootImage("Score: "+score,30,Color.black, Color.white));}Compile and correct any errors

Greenfoot Activity Now, we need to add an instance of the Label class to our world. Open the code editor of the Space class, declare a new object of class label (after the Space Class declaration the before the constructor.private Label scoreLabel;

Add code to the constructor of the world, to create a Label object, and place it in the World Label scoreLabel = new Label(); addObject(scoreLabel,60,380);

Compile and test your code. You should now see your score at the bottom left of the screen (although we still need to add code to make it update!)

Greenfoot Activity To understand the relationship between our objects, the diagram below illustrates how they currently interact.

The Space class creates instances of the Rocket, Alien and Label classes, and the Rocket creates instances of the Shot class when the space bar is pressed.SpaceLabelRocketAlienShot

Greenfoot Activity To update the score, we would need to do this in the Shot class, as this is where checks for collisions with the Alien Class take place.The problem we have is that the Shot class and the Label class have no way of communicating directly (as they are not visible to each other).To solve this issue, we can pass a reference to the Label when we create the Rocket, and then pass this to the instances of the Shot class when they are created. This will allow the Shot class to call the UpdateScore () method of the Label when a collision with an Alien takes place.This is much simpler than it sounds, and only requires a few alterations to our existing code!

Greenfoot Activity

The Shot class will then be able to call the updateScore() method of the LabelupdateScore()

Greenfoot Activity First we need to make some changes to the constructor of the Rocket ClassOpen the code editor for the Rocket classDeclare a class-level private attribute of type Label, and name it tempLabel (below the existing variable for private int shotTimer=0;)public Label tempLabel;Create a new constructor to take the label as a parameter and assign it to the tempLabel we have created public Rocket(Label inLabel) { tempLabel= inLabel; }In the act() method of Rocket, where the code creates a new shot (when the space bar is pressed), amend the code to pass tempLabel to the Shot:getWorld().addObject(new Shot(tempLabel),getX(),getY());

Greenfoot Activity We need to make similar changes to the Shot class. Create a class level variable for tempLabel, and create a constructor to accept a label as a parameter, and assign to our new tempLabel.Open the code editor for the shot class and amend as shown:public class Shot extends Actor{ private Label tempLabel; public Shot(Label inLabel) { tempLabel=inLabel; }

Greenfoot Activity Next, we need to add one line of code in the Shots act() method if (getY() > 0) { setLocation(getX(), getY()-5); Actor hit = getOneIntersectingObject(Alien.class); if (hit != null) { tempLabel.updateScore(10); getWorld().removeObject(hit); getWorld().removeObject(this); } } else { getWorld().removeObject(this); }This calls the Labels updateScore() method adding the value 10 to the score

Greenfoot Activity Now we need to make one change to the world class. Open the code editor for the Space Class.Amend the line of code in the constructor that adds a new Rocket to the world, to pass the scoreLabel as a parameter

super(600, 400, 1); Label scoreLabel = new Label(); addObject(scoreLabel,60,380); addObject(new Rocket(scoreLabel),300,340);

Compile, run and test, the score should now increase by 10 points every time an alien is hit.

*Oracle Academy Java Fundamentals Institute: Day 1Greenfoot Activity We now have a working scenario which allows keyboard control and interaction between Actors in our world.

Possible Additions :

End game scenarios :Alien crashes into RocketAlien reaches earthNo Aliens left (add more Aliens)TimerAlien shoots backMultiple rows of AliensLevels

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space wars