Java questions which don't deserve their own thread, yet.

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Jehde: Apr 21, 2010

I'm creating a simple game, main algorithm for the game is in a main method along with this additional method on how to choose the player difficulty:

code:

    private void createPlayerOne(int difficulty, int startx, int starty, int tactic)
    {
    	if (difficulty == 1)
    	{
    		Easy player = new Easy(startx, starty);
    	}
    	else if (difficulty == 2)
    	{
    		Medium player = new Medium(startx, starty);
    	}
    	else if (difficulty == 3)
    	{
    		Hard player = new Hard(startx, starty);
    	}
    	else
    	{
    		Expert player = new Expert(startx, starty, tactic);
    	}
    }

But ofcourse these are initialized out of scope, is there any way to get around this?

# ? Dec 6, 2010 13:41

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# ? Apr 25, 2024 00:56

Paolomania: Apr 26, 2006

What language are you coming from? It is fairly clear that you are not "thinking in Java".

# ? Dec 6, 2010 14:51

epswing: Nov 4, 2003; Soiled Meat

You probably want something more like...

code:

    
abstract class Player { ... }
class EasyPlayer extends Player { ... }
class MediumPlayer extends Player { ... }
class HardPlayer extends Player { ... }
class ExpertPlayer extends Player { ... }

private Player createPlayer(int difficulty, int startx, int starty, int tactic)
{
    Player player;
    
    switch (difficulty) {
        case 1:
            player = new EasyPlayer(startx, starty);
            break;
        case 2:
            player = new MediumPlayer(startx, starty);
            break;
        case 3:
            player = new HardPlayer(startx, starty);
            break;
        default:
            player = new ExpertPlayer(startx, starty, tactic);
    
    return player;
}

E: The idea that you can do Player p = new EasyPlayer() is called polymorphism.

epswing fucked around with this message at 16:07 on Dec 6, 2010

# ? Dec 6, 2010 15:58

Dub Step Dad: Dec 29, 2008

Recently I've begun taking classes at my university in Java, which is my first language, so I have a question that's probably pretty simple.
We just started covering MVC architecture, and in a project we're doing I have to create a class "Tile" that extends JButton, and then in my GUI create a 9x9 2D array of Tile objects to be displayed as a big square of buttons, and then using a set of radio buttons and a combo box I can set the background and the foreground of the tiles. Holding the Color information of the tiles I have another array of a class, TileInfo.
My problem is that my Tile class is my view, the main GUI class is the controller, and the TileInfo is the model, but when my ActionListener for the tiles is called, I don't know how I can make my program differentiate between different objects in the Array without creating 81 if statements, and then after that be able to reference the TileInfo object that corresponds to the Tile.

# ? Dec 6, 2010 18:33

tef: May 30, 2004; -> some l-system crap ->

epswing posted:

You probably want something more like...

An enum for difficulty, stored as an attribute somewhere it makes sense.

# ? Dec 6, 2010 19:34

epswing: Nov 4, 2003; Soiled Meat

His program might depend on the implementation of each player class...

:negative:

# ? Dec 6, 2010 19:41

Parantumaton: Jan 29, 2009; The OnLy ThInG
i LoVe MoRe
ThAn ChUgGiNg SeMeN
iS gEtTiNg PaId To Be A
sOcIaL MeDiA sHiLl
FoR mIcRoSoFt
AnD nOkIa

epswing posted:

His program might depend on the implementation of each player class...

...so it should be encapsulated inside the player class itself to avoid doing extra conditionals in various places.

Well OK, "player" as a class concept for difficulty most likely isn't the correct place for that code but anyways.

# ? Dec 6, 2010 19:50

epswing: Nov 4, 2003; Soiled Meat

I don't presume to know how you're building your program. I'm just showing you a way to create and return a new Player, because your original problem was scope.

# ? Dec 6, 2010 19:54

ShardPhoenix: Jun 15, 2001; Pickle: Inspected.

Puppet Pal Claudius posted:

Recently I've begun taking classes at my university in Java, which is my first language, so I have a question that's probably pretty simple.
We just started covering MVC architecture, and in a project we're doing I have to create a class "Tile" that extends JButton, and then in my GUI create a 9x9 2D array of Tile objects to be displayed as a big square of buttons, and then using a set of radio buttons and a combo box I can set the background and the foreground of the tiles. Holding the Color information of the tiles I have another array of a class, TileInfo.
My problem is that my Tile class is my view, the main GUI class is the controller, and the TileInfo is the model, but when my ActionListener for the tiles is called, I don't know how I can make my program differentiate between different objects in the Array without creating 81 if statements, and then after that be able to reference the TileInfo object that corresponds to the Tile.

It's hard to say without seeing the code in more detail, but it sounds like you want to do something like storing the x coordinate and y coordinate of the tiles (or some other unique identifier) in both the Tile and TileInfo objects, which will allow you to check which corresponds to which. The most straightforward thing would be for Tile to have a direct reference to TileInfo, but I'm not sure if that would make sense in your specific case.

# ? Dec 7, 2010 01:02

Lumpy: Apr 26, 2002; La! La! La! Laaaa!; College Slice

I have created an SSL socket server, I think correctly using code similar to:

code:

SSLServerSocketFactory ssocketFactory = (SSLServerSocketFactory) SSLServerSocketFactory.getDefault();
server = ssocketFactory.createServerSocket(port);

where server is an SocketServer and port == 443

I have created a certificate using:

keytool -genkey -keystore mySrvKeystore -keyalg RSA

I have code else where that starts a listener and accepts when a connection is made.

I started up the java server with the additional vm params:

-Djavax.net.ssl.keyStore=<the store filename> -Djavax.net.ssl.keyStorePassword=<the password>

I created a quick java client to connect (and have also used openssl for testing). I see on the server side the connection made, but the client:

1. Cannot retrieve the certificate for viewing
2. Writes data on the socket, but nothing appears on the server side

What am I missing?

# ? Dec 7, 2010 17:34

Janitor Prime: Jan 22, 2004; PC LOAD LETTER

What da fuck does that mean; Fun Shoe

You need to use the certificate you created in your client and add it to the truststore for the SSLConnectionFactory or whatever it's called before trying to connect to the server. Or you can disable the check for the server's certificate but that's not a good idea in the real world.

Oh also make sure that your certificate includes your hostname in the common name field.

# ? Dec 7, 2010 17:50

DholmbladRU: May 4, 2006

I am trying to create a server and client java classes that communicate through socket. I can create a connection, however when I attempt to pass data I get a null pointer.

I can successfully connect, however I am having some problems passing messages back and fourth.

code:

try{
					message = (String)in.readObject();
					System.out.println("Enter either add or mult and two integers");
					s = new Scanner(System.in);
					while(s.nextLine() != null){
						String temp = s.nextLine();
						sendMessage(temp);


						
					}
				}

And here is where I am receiving the message.

code:

	try{
					message = (String)in.readObject();
					s = new Scanner(message);
					System.out.println(message);
					String operator = s.next();
					System.out.println(operator);
					int numA = Integer.parseInt(s.next());
					System.out.println(numA);
					int numB = Integer.parseInt(s.next());
					System.out.println(numB);
					int tempInt = 0;
					if (operator.equals("add") && operator != null)
						
						tempInt = numA+numB;
						sendMessage(tempInt+"");
				}

Haven't programed java that much, so im probably breaking a number of rules.

# ? Dec 7, 2010 21:32

epswing: Nov 4, 2003; Soiled Meat

Where (which line) does the NPE occur?

You're not showing us enough code. Show us the sendMessage method, and the rest of the body of your receiveMessage method.

# ? Dec 7, 2010 21:43

DholmbladRU: May 4, 2006

send method was taken from the fallowing, http://zerioh.tripod.com/ressources/sockets.html

This seems to be doing what I need it to on the client side.

code:

try{
					message = (String)in.readObject();
					System.out.println("Enter either add or mult and two integers");
					s = new Scanner(System.in);
					while(s.hasNext() || message !=null){
						String temp = s.nextLine();
						sendMessage(temp);
					
					}
				}

code:

message = (String)in.readObject();
					s = new Scanner(message);
					System.out.println(message);
					String operator = s.next();
					int numA = Integer.parseInt(s.next());
					int numB = Integer.parseInt(s.next());
					
					int tempInt = 0;
					if (operator.equals("add") && operator != null){
						tempInt = numA+numB;
						System.out.println("server>" + tempInt);
						sendMessage(tempInt+"");
						
					}if(operator.equals("mult") && operator != null){
						tempInt = numA*numB;
						System.out.println("server>" + tempInt);
					}

This all works properly, however the wrong class is sending out the answer. I need the answer of 'add 10 10' to be output to the clients console. At the moment it is output by the servers console in this line
'System.out.println("server>" + tempInt);'

DholmbladRU fucked around with this message at 22:49 on Dec 7, 2010

# ? Dec 7, 2010 21:47

fletcher: Jun 27, 2003; ken park is my favorite movie; Cybernetic Crumb

Instead of:

while(s.nextLine() != null)

don't you want:

while (s.hasNextLine())

# ? Dec 7, 2010 22:50

DholmbladRU: May 4, 2006

thanks got that all figured out. havnt programed any java in awhile.

# ? Dec 8, 2010 00:29

Trick Question: Apr 9, 2007

I am trying to use a priority queue to hold objects for a game I and some others are creating, as such:

code:


...
public Hand()
	{
		Comparator<Card> comparator1 = new CardComparator();
		ourHand = new PriorityQueue<Card>(108, comparator1);
	}
	
	public class CardComparator implements Comparator<Card>
	{
		public CardComparator(){
			super();
		}
		
		public int compare(Card c, Card d)
		{
			if(c.getSuit() > d.getSuit()) return 1;
			if(c.getSuit() < d.getSuit()) return -1;
			if(c.getValue() < d.getValue()) return -1;
			if(c.getValue() > d.getValue()) return 1;
			else return 0;
		}
	}
...

The problem is, I can't remove anything from this queue, and it doesn't actually sort the contained objects in any way, shape, or form. So, what am I loving up?

# ? Dec 8, 2010 22:10

Surface: May 5, 2007; <3 boomstick

Trick Question posted:

I am trying to use a priority queue to hold objects for a game I and some others are creating...

Doesn't look like the problem is here, what method are you using to remove something

code:

ourHand.remove(aCardObject)

should work... I can't see a reason it wouldn't work unless you are doing something like:

code:

Card spades5 = new Card(Spades,5);
Card anotherSpades5 = new Card(Spades,5);
ourHand.add(spades5);
ourHand.remove(anotherSpades5); //wont do anything

This wont work because even though both cards are 5 of spades, they are two different instances, and PriorityQueue tests for object equality via object.equals(object2);

If you override the .equals() and .hashCode() method of your card class the above code will work, but instead consider only instantiating one card object per card.

As for the sorting, does this line of the PriorityQueue javadocs apply to you:

JavaDocs posted:

The Iterator provided in method iterator() is not guaranteed to traverse the elements of the PriorityQueue in any particular order. If you need ordered traversal, consider using Arrays.sort(pq.toArray()).

Surface fucked around with this message at 21:28 on Dec 9, 2010

# ? Dec 8, 2010 22:47

brosmike: Jun 26, 2009

To clarify, if you mean you want to remove the highest-priority item in the queue, the method you're looking for is poll, not remove.

# ? Dec 8, 2010 23:05

epswing: Nov 4, 2003; Soiled Meat

Surface alluded to this, but I'll make it clear.

When ~~using collection-like classes (List, Set, Map, Queue, etc)~~ writing anything non-trivial, you really should properly implement .equals() and .hashCode() methods for the objects you want to reference, otherwise Java won't really understand how to compare anything, and you'll end up with undefined behavior that'll make you want to set yourself on fire.

# ? Dec 9, 2010 00:32

Internet Janitor: May 17, 2008; "That isn't the appropriate trash receptacle."

Epswing is totally on the money here. And whatever you do, don't just overload .equals() and leave .hashCode() as the default implementation- it'll violate the .equals() contract and gently caress things up in hilariously subtle ways.

# ? Dec 9, 2010 06:45

Paolomania: Apr 26, 2006

especially if you are fond of using HashMap and HashSet

# ? Dec 9, 2010 19:26

Surface: May 5, 2007; <3 boomstick

Internet Janitor posted:

Epswing is totally on the money here. And whatever you do, don't just overload .equals() and leave .hashCode() as the default implementation- it'll violate the .equals() contract and gently caress things up in hilariously subtle ways.

Haha yes I should edit this into my post.

# ? Dec 9, 2010 21:28

Flobbster: Feb 17, 2005; "Cadet Kirk, after the way you cheated on the Kobayashi Maru test I oughta punch you in tha face!"

What's really fun is teaching students in a second-semester Java data structures class the proper way to implement equals and hashCode, especially when the concept of hash tables hasn't been introduced yet so a hash code seems pointless to them. (Why teach hashCode without mentioning hash tables? If we're teaching them to override equals, it's better that we mention hashCode at the same time since the two are so closely related.)

I saw so much of this last semester:

code:

public boolean equals(Object other)
{
    return hashCode() == other.hashCode();
}

Some students at least understood that you could use the hashcodes to short-circuit for inequality but that it doesn't say anything about equality, but even that makes my skin crawl a little bit for some reason.

# ? Dec 9, 2010 22:04

Fly: Nov 3, 2002; moral compass

Flobbster posted:

code:

public boolean equals(Object other)
{
    return hashCode() == other.hashCode();
}

Please teach them. I've been seeing this in job candidates, too. :ughh:

# ? Dec 9, 2010 23:30

Janitor Prime: Jan 22, 2004; PC LOAD LETTER

What da fuck does that mean; Fun Shoe

Flobbster posted:

What's really fun is teaching students in a second-semester Java data structures class the proper way to implement equals and hashCode, especially when the concept of hash tables hasn't been introduced yet so a hash code seems pointless to them. (Why teach hashCode without mentioning hash tables? If we're teaching them to override equals, it's better that we mention hashCode at the same time since the two are so closely related.)

I saw so much of this last semester:
code:
public boolean equals(Object other)
{
    return hashCode() == other.hashCode();
}
Some students at least understood that you could use the hashcodes to short-circuit for inequality but that it doesn't say anything about equality, but even that makes my skin crawl a little bit for some reason.

I always thought the contract for hashCode was that it had to match the same things that equals did, but after reading the spec that's not the case. God drat that's a terrible way to introduce subtle bugs.

That code is still inexcusable, they should at least check for nulls and that's its the same type!

# ? Dec 10, 2010 01:27

trex eaterofcadrs: Jun 17, 2005; My lack of understanding is only exceeded by my lack of concern.

MEAT TREAT posted:

I always thought the contract for hashCode was that it had to match the same things that equals did, but after reading the spec that's not the case. God drat that's a terrible way to introduce subtle bugs.

That code is still inexcusable, they should at least check for nulls and that's its the same type!

Whoops missed an important word! nvm this

# ? Dec 10, 2010 01:29

Trick Question: Apr 9, 2007

Thanks for all the help. After adding

code:

public boolean equals(Object card2){
	   if(card2 instanceof Card){
		   if(value == ((Card) card2).getValue() && suit == ((Card) card2).getSuit()){
			   return true;
		   }
		   return false;
	   }
	   else return false;
   }
   
   public int hashCode(){
	   int suitOffset = 15*suit;
	   int returnCode = suitOffset + value;
	   return returnCode;
   }

The remove works just fine, and our game is basically working. Still, it ain't quite sorting as I'd like it to. Anyone have any idea why this is?

# ? Dec 10, 2010 02:42

Necc0: Jun 30, 2005; by exmarx; Broken Cake

for the life of me I can't figure out how graphics2D is supposed to work. the two relevant classes:

http://pastebin.com/vMsCXtcC

and:

http://pastebin.com/PjzNe2hD

I've tried setting jPanel1 equal to the draw object, then running the draw object. I've tried passing display.jPanel1 into the drawImage functions, and now I've tried the current iteration. No matter what I do I get nothing to the screen.

I know the images are in the right place because the older iteration of this program was just using the graphics library to draw, and while it worked it looked terrible and took forever to refresh.

edit: sorry about all the commented out lines I've been throwing poo poo at this for a few hours now and I know it's something really minor and easy

edit2: not nearly as annoying now

Necc0 fucked around with this message at 05:12 on Dec 10, 2010

# ? Dec 10, 2010 04:07

RitualConfuser: Apr 22, 2008

Trick Question posted:

The remove works just fine, and our game is basically working. Still, it ain't quite sorting as I'd like it to. Anyone have any idea why this is?

In what way is it not sorting correctly?

# ? Dec 10, 2010 04:24

fletcher: Jun 27, 2003; ken park is my favorite movie; Cybernetic Crumb

Necc0 posted:

for the life of me I can't figure out how graphics2D is supposed to work. the two relevant classes:

Might wanna use something like http://www.pastebin.com/ instead of posting a ton of code in the thread.

# ? Dec 10, 2010 04:48

Trick Question: Apr 9, 2007

RitualConfuser posted:

In what way is it not sorting correctly?

Preferably, I'd have it sorting by suit then value. However, right now, it doesn't appear to be sorting at all, as such:

code:

[1 of Red, 2 of Red, 2 of Blue, wild draw four of Black, 7 of Red, 2 of Green, 2 of Yellow]

I'd assumed making a comparator for it like

code:

private PriorityQueue<Card> ourHand;
private Comparator<Card> comparator1;
...
public Hand()
	{
		comparator1 = new CardComparator();
		ourHand = new PriorityQueue<Card>(108, comparator1);
	}

...
public class CardComparator implements Comparator<Card>
	{
		public CardComparator(){
			
		}
		
		public int compare(Card c, Card d)
		{
			if(c.getSuit() > d.getSuit()) return 1;
			if(c.getSuit() < d.getSuit()) return -1;
			if(c.getValue() < d.getValue()) return -1;
			if(c.getValue() > d.getValue()) return 1;
			else return 0;
		}
	}

would cause it to sort like that, but it doesn't seem to have worked. Any advice?

# ? Dec 10, 2010 04:57

RitualConfuser: Apr 22, 2008

I made a simple implementation of Card with suit and value as int's and it sorts fine for me using that Comparator. What does the implementation of Card look like?

# ? Dec 10, 2010 05:09

Necc0: Jun 30, 2005; by exmarx; Broken Cake

fletcher posted:

Might wanna use something like http://www.pastebin.com/ instead of posting a ton of code in the thread.

thanks a bunch

# ? Dec 10, 2010 05:11

Trick Question: Apr 9, 2007

RitualConfuser posted:

I made a simple implementation of Card with suit and value as int's and it sorts fine for me using that Comparator. What does the implementation of Card look like?

Like this.

be forewarned, I probably haven't commented that as well as I should have.

# ? Dec 10, 2010 05:53

RitualConfuser: Apr 22, 2008

OK, the issue is in the comparator. Basically, you need a simple way to generate a unique number for each suit/value combo such that it maintains ordering (hint: it's already somewhere in your code). Then in the comparator, you can return the difference of the 2 card's unique numbers. So, if you had a deck of 52 cards, how would you order them such that the cards are assigned a unique number between 0 and 51? Does that make sense? You could also use something other than a PriorityQueue but that might require more changes in your code.

E: I probably should have tested that out first... I think what you might be looking for is a SortedSet instead of a PriorityQueue. That assumes that you can't have more than one card of the same suit/value though, which may not be what you want.

RitualConfuser fucked around with this message at 07:13 on Dec 10, 2010

# ? Dec 10, 2010 06:34

rjmccall: Sep 7, 2007; no worries friend; Fun Shoe

RC: what you even I don't know

TQ, neither Card and CardComparator is the source of your bugs. You problem is that you have code that looks something like this:

code:

for (Card c : ourHand) { ... }

This is wrong because PriorityQueue does not guarantee that it will keep the entire queue sorted at all times; it guarantees only that, at any given point, the element returned by peek() and poll() will not be greater than anything left in the queue.

I know you are doing this, or something equivalent, because these elements are actually in heap order, where the element at index N is smaller than the elements at index 2(N+1)-1 and 2(N+1). That is because PriorityQueue is internally implemented using the "heap" data structure.

What you should be doing instead is something like:

code:

while (!ourHand.empty()) { Card c = ourHand.poll(); ... }

# ? Dec 10, 2010 06:55

RitualConfuser: Apr 22, 2008

rjmccall posted:

RC: what you even I don't know

For some reason I was thinking that the value returned from the comparator was being used as the priority and causing the sorting to be dependent upon the order in which the values were added... which wouldn't be much of a sort. And now I don't even know how I got to that conclusion.

TQ: what was the purpose of keeping the cards in a queue rather than a set or other collection?

# ? Dec 10, 2010 07:11

Trick Question: Apr 9, 2007

The main purpose was that i could just import the priorityQueue and it'd auto-sort real easy.

# ? Dec 10, 2010 08:07

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# ? Apr 25, 2024 00:56

RitualConfuser: Apr 22, 2008

What I'm getting at is that using a queue would suggest that the cards are going to be queued and then dequeued at some point. But, it seems like you'd probably want to iterate through the hand multiple times, and as rjmccall and Surface said, you can't iterate through the items in a PriorityQueue in sorted order without dequeueing them. So, if you need the ability to iterate through the cards multiple times (in order), then it's probably not the right structure.

RitualConfuser fucked around with this message at 08:43 on Dec 10, 2010

# ? Dec 10, 2010 08:40

The Something Awful Forums > Discussion > Serious Hardware/Software Crap > The Cavern of COBOL > Java questions which don't deserve their own thread, yet.

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