Applet Orchard

Java Programming: Let’s Build a Game #5

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In this video we take care of full on collision within our game and also a particle trail effect. If you have any questions then be sure to leave a comment or contact me on twitter; realtutsgml. If you learned something then be sure to leave a like, comment, and favorite.

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42 responses to “Java Programming: Let’s Build a Game #5”

  1. skuul88 Avatar
    skuul88

    ok so im pretty new to this whole programming thing, and I managed to set the ID of the trail to BasicEnemy. This caused a collision issue where the trail was colliding with the enemy square due to the nature of the collision method and how it loops through the whole object list. I was able to locate and remedy the issue after about 10 minutes, and it felt so damn good.

    Reply
  2. Kyle Pereira Avatar
    Kyle Pereira

    How are you not getting ConcurrentModificationExceptions rn?

    Reply
  3. Scarlet Chiira Avatar
    Scarlet Chiira

    I did the exact same stuff as in the video but somehow I botched it and its not working. I was having real fun with this but sadly I can't continue because there's no source code. And if there is then if you have to buy it. I'm not going to, because that is a poor way to actually educate someone on how to build a game. If you want to educate people at least lend the source code off to a repository on GitHub so that way people can write the code at their own pace and see where they made the mistake.

    Reply
  4. swishy _ fishy Avatar
    swishy _ fishy

    lol i thought he said in our sex method at: 1:58

    Reply
  5. Your Average Joe Avatar
    Your Average Joe

    For anyone having trouble with key inputs, (pressing multiple keys at once causes the player to stop moving in the correct direction) here are the correct functions for the KeyInput class

    public void keyPressed(KeyEvent e) {
    int key = e.getKeyCode();

    for(int i = 0; i < handler.object.size(); i++) {
    GameObject tempObject = handler.object.get(i);

    if(tempObject.getId() == ID.Player) {
    //key events for player

    if(key == KeyEvent.VK_W) tempObject.setVelY(tempObject.getVelY()-5);
    if(key == KeyEvent.VK_A) tempObject.setVelX(tempObject.getVelX()-5);
    if(key == KeyEvent.VK_S) tempObject.setVelY(tempObject.getVelY()+5);
    if(key == KeyEvent.VK_D) tempObject.setVelX(tempObject.getVelX()+5);
    tempObject.setVelY(Game.clamp(tempObject.getVelY(),-5,5));
    tempObject.setVelX(Game.clamp(tempObject.getVelX(),-5,5));
    }
    }

    if(key == KeyEvent.VK_ESCAPE) System.exit(1);
    }

    public void keyReleased(KeyEvent e){
    int key = e.getKeyCode();

    for(int i = 0; i < handler.object.size(); i++) {
    GameObject tempObject = handler.object.get(i);

    if(tempObject.getId() == ID.Player) {
    //key events for player

    if(key == KeyEvent.VK_W) tempObject.setVelY(tempObject.getVelY()+5);
    if(key == KeyEvent.VK_A) tempObject.setVelX(tempObject.getVelX()+5);
    if(key == KeyEvent.VK_S) tempObject.setVelY(tempObject.getVelY()-5);
    if(key == KeyEvent.VK_D) tempObject.setVelX(tempObject.getVelX()-5);
    tempObject.setVelY(Game.clamp(tempObject.getVelY(),-5,5));
    tempObject.setVelX(Game.clamp(tempObject.getVelX(),-5,5));
    }
    }

    }

    Reply
  6. Zachary Young Avatar
    Zachary Young

    in the method public Rectangle getBounds() in the BasicEnemy class, if you use: return new Rectange(velX, velY, 16, 16); instead of x and y, it is much smoother than using x & y.

    Reply
  7. Karex_ Avatar
    Karex_

    i don't know why but my health doesn't go down for some reason. Can someone please help me? 11:03

    Reply
  8. Vitex Avatar
    Vitex

    This is actually really fun, I've never had so much fun on a 2D game before, this is great! Thank you <3

    Reply
  9. Robert Balassan Avatar
    Robert Balassan

    anyone got any suggestion on how to differentiate player 1 from player 2 in the getBounds method? (i kept the game 2 players) the problem is when any player collides both health bars decrease

    Reply
  10. Marcus Case Avatar
    Marcus Case

    Just wondering, in that for loop, u make a temporary object. Would it be faster memory wise to have tempObject as a local variable, and set it to the handler.object.get(i), and then set it to null afterwards?

    Reply
  11. SauceMaster2K Avatar
    SauceMaster2K

    Why does it say Exception in thread "Thread-2" java.lang.IllegalArgumentException: alpha value out of range

    Reply
  12. Ephraim Bane Avatar
    Ephraim Bane

    ===============================
    HELP HELP HELP HELP HELP HELP
    HELP HELP HELP HELP HELP HELP
    ===============================

    No trail shows up, as far as I know it's not creating the object.
    Code:
    In BasicEnemy:
    public void tick() {
    x += velX;
    y += velY;

    if (y <= 0 || y >= Game.HEIGHT – 45) velY *= -1;
    if (x <= 0 || x >= Game.WIDTH – 22) velX *= -1;

    handler.addObject(new Trail(x, y, ID.Trail, Color.red, 16, 16, 0.01f, handler));
    }

    Reply
  13. Rens Hulsebosch Avatar
    Rens Hulsebosch

    I fucked up, but don't know where… And you didn't post source code. Shame, I was enjoying this…

    Reply
  14. TheBrohman Avatar
    TheBrohman

    I have an issue. In my player class It can't get "handler.object.size" because "object" is not public. Do I need to change it to public or have I missed something? I do have "private Handler handler;" and "this.handler = handler" etc.

    Reply
  15. Or Dadush Avatar
    Or Dadush

    hi I'm having a problem about min 23I run the game and after a second the Player and the BasicEnemy disappears (the HUD not) I don't get any error the game is still running I have no idea what do to someone has any answer

    Reply
  16. Teofilo Francisco Avatar
    Teofilo Francisco

    Hi, I was having an error: java.util.ConcurrentModificationException, because I used an iterator to loop over the GameObject list, then I used a CopyOnWriteArrayList and every thing goes well. Thanks for your tutorial.

    Reply
  17. Remag Avatar
    Remag

    Whenever I run it the trails are synced but they don't line up which causes them to move at the same time but when I press w the trail moves left and the player move up. PLZ Help

    Reply
  18. SkViX Avatar
    SkViX

    If your getting an error "Thread-2". Its because u haven't written Handler code in player class 8:11

    Reply
  19. Smily Clown Avatar
    Smily Clown

    handler.addObject(new Trail(x + 4, y + 4, ID.Trail, Color.WHITE, 24, 24, 0.02f, handler));

    for better effect on player's trail.
    If trails is equal to player, when you move horizontal or vertical it looks like a line.
    So i make trail smaller and now you can see where is head and where is trail.

    Reply
  20. Nicolas Bohnenberger Avatar
    Nicolas Bohnenberger

    As soon as I run the code with the collision method I get a NullPointerExpection coming from the loop. Just throws the error:

    Exception in thread "Thread-2" java.lang.NullPointerException
    at com.frogger.Player.tick(Player.java:25)
    at com.frogger.Handler.tick(Handler.java:19)
    at com.frogger.Game.tick(Game.java:76)
    at com.frogger.Game.run(Game.java:59)
    at java.lang.Thread.run(Unknown Source)

    +RealTutsGML any idea why?

    Reply
  21. TRESCHK Avatar
    TRESCHK

    I'm getting an error:

    Exception in thread "Thread-2" java.lang.NullPointerException
    at java.awt.Rectangle.intersects(Unknown Source)
    at de.cryptodev.game2.main.Player.collision(Player.java:38)
    at de.cryptodev.game2.main.Player.tick(Player.java:23)
    at de.cryptodev.game2.main.Handler.tick(Handler.java:14)
    at de.cryptodev.game2.main.Game.tick(Game.java:86)
    at de.cryptodev.game2.main.Game.run(Game.java:67)
    at java.lang.Thread.run(Unknown Source)

    Reply
  22. Adam Hussain Avatar
    Adam Hussain

    My player is laggy anyone know how to fix it.It has something to do with the buffer strategy

    Reply
  23. Mahdi Avatar
    Mahdi

    This is quite old but I have the code perfectly fine but I keep getting lag spikes every 5-10 seconds and it gets worse after every spike does anyone know how to fix that?

    Reply
  24. Roy Westerhof Avatar
    Roy Westerhof

    the line "else handler.removeObject(this);" makes the game crash for me… why?

    Reply
  25. ⊆Roovy⊇ Avatar
    ⊆Roovy⊇

    Dat lion!

    Reply
  26. Sasha Omerasvic Avatar
    Sasha Omerasvic

    for the if(getBounds().intersects(tempObject.getBounds())){
    I keep getting an error under the second getBounds. Any idea why?

    Reply
  27. Kimera / キメラ Avatar
    Kimera / キメラ

    For those getting errors with the collision function in the "player class", make sure you added this line of code in the "public Player": this.handler = handler;
    I did that and it cleared the problem right up and now it works as intended

    Reply
  28. MrBearcat82 Avatar
    MrBearcat82

    Totally been using these videos for an FBLA State competition learning tool!

    Reply
  29. PumpkiNot Avatar
    PumpkiNot

    Is the whole video about trails?

    Reply
  30. Manfred Orse Avatar
    Manfred Orse

    7:20 is it colliding if its fully inside?

    Reply
  31. Chocolate Storm Avatar
    Chocolate Storm

    my game starts stuttering when i add trails… any ideas?

    Reply
  32. Cosme Tejeda Avatar
    Cosme Tejeda

    Is there a way to edit the code so the BasicEnemy bounces off of the Player when hit instead of going through?

    What I did was make another collision method for the BasicEnemy and if it collides with the player I changed the BasicEnemy's velX *= -1 and velY *= -1 but sometimes the player will keep moving towards the enemy and a weird glitch will happen. Is there a more efficient way to do this?

    Reply
  33. Sam Mader Avatar
    Sam Mader

    Can't fix a bug where my health drops to 0 after one hit. Everything is the same as in his code.

    Reply
  34. The Gaming Koala Avatar
    The Gaming Koala

    im making a tower defense type of game, so im having the towers attacking the soldiers, i have them all placed and moving how id like(besides the fact id like the hitbox to be a circle) . this is what id like to know. how would i go about making the towers hitting one enemy at a time, and hitting the closest one. and how would i make the hitbox being a circle

    Reply
  35. LOST CHROMEAZONE Avatar
    LOST CHROMEAZONE

    Trying to keep up with the furious typing is actually really fun to do

    Reply
  36. Bananasfan Avatar
    Bananasfan

    there is something wrong with the controlls when ever im using it for a little while the controlls stop working

    Reply
  37. Pop Club Avatar
    Pop Club

    Anyone's Game Freezing after adding the Trail? Here's a fix!

    Check your Handler Class and see if the addObject and removeObject methods are exactly like this:

    public void addObject(GameObject object){
    this.object.add(object);
    }

    public void removeObject(GameObject object){
    this.object.remove(object);
    }

    Reply
  38. Tim Studio Avatar
    Tim Studio

    Health bar is not getting low need help. Please do something.

    Reply
  39. Raxx Scar Avatar
    Raxx Scar

    i love your desktop picture!

    Reply
  40. Raxx Scar Avatar
    Raxx Scar

    HAHAHAHAH I WAS DOING THAT ALL IN BASICENEMY LOLOLOL… mb

    Reply
  41. Rhoncus Vitae Avatar
    Rhoncus Vitae

    My player trail refuses to be any size other than 16, 16. I copied
    handler.addObject(new Trail(x, y, ID.Trail, Color.red, 16, 16, 0.05f, handler));
    from BasicEnemy class into Player class and changed it to
    handler.addObject(new Trail(x, y, ID.Trail, Color.white, 32, 32, 0.05f, handler));

    The color changed to white but the size of the trail didn't.

    Reply
  42. LGsmoesie Avatar
    LGsmoesie

    I'm trying to follow along with the series so I'm doing everything the same as you (apparently not) and there's no error in my code. Still, when I'm launching the game there is no trail. Can anyone tell what is wrong or what could be wrong?

    Reply

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