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Java Forum / First Aid / February 2005Get array index on MouseEvent
Hi, Is it possible to get the index of an item stored in an array via a MouseEvent? E.g., if a GUI uses a JLabel array to create a grid of JLabels, and a MouseListener is used on each JLabel, can the index of a given JLabel be retrieved when a user clicks on it? The following code will hopefully clarify what I'm asking: =================================================== private JLabel[] lblArray = new JLabel[8]; public void addArray() { for (int i = 0; i < lblArray.length; i++) { lblArray[i] = new JLabel("" + i); lblArray[i].addMouseListener(this); add(lblArray[i]); } } public void mouseClicked(MouseEvent e) { JLabel tempLabel = (JLabel)e.getSource(); // Creates reference to orig object... is this necessary to get index? // Imaginary use of "getIndex()". There're a lot of "getIndex()" methods in the API, but none seem to apply here... not sure what to do. JOptionPane.showMessageDialog(null, tempLabel.getIndex()); } =================================================== Thanks. One suggestion I would have is to make a simple extension of JLabel called MyJLabel. Add one field to it that's an int. When you create the MyJLabel, send all of the usual information to the JLabel class through the constructor of MyJLabel and set the value of the int to the index of the MyJLabel in the array. Then when you cast the source to a MyJLabel, just retrieve the value of the int. klynn47@comcast.net coughed up: > One suggestion I would have is to make a simple extension of JLabel > called MyJLabel. Add one field to it that's an int. [quoted text clipped - 5 lines] > Then when you cast the source to a MyJLabel, just retrieve the value > of the int. IMHO, this is not particularly clean. That would mean having the object itself be cognizant of its own order in a wrapping list somewhere. What if the object was added to multiple lists, or if one of the JLabel's is removed from the list? Seems a little like inverted incapsulation to me. If you have a ArrayList of JLabels, then use the getIndex() method on the list itself. IOW, have the container be in charge of what it regards as the index, and not the object itself. and *to the OP*, why do you find it necessary to know the index anyway? If you have the JLabel itself, isn't that all you need? Are you trying to maintain parallel arrays?  Signature"It's easier to be terrified by an enemy you admire." -Thufir Hawat, Mentat and Master of Assassins to House Atreides Thomas G. Marshall coughed up: > klynn47@comcast.net coughed up: >> One suggestion I would have is to make a simple extension of JLabel [quoted text clipped - 11 lines] > That would mean having the object itself be cognizant of its own > order in a wrapping list ...or array, of course... > somewhere. What if the object was added to > multiple lists, or if one of the JLabel's is removed from the list? Seems [quoted text clipped - 9 lines] > anyway? If you have the JLabel itself, isn't that all you need? Are > you trying to maintain parallel arrays? Signature"It's easier to be terrified by an enemy you admire." -Thufir Hawat, Mentat and Master of Assassins to House Atreides Jay skrev: > Hi, > [quoted text clipped - 25 lines] > > Thanks. If you had your labels in an ordered collection (such as an ArrayList), you should be able to get the index like so: mylabelCollection.getIndx(evt.getSource()); Another way would be to map label vs. index separately (e.g. HashMap?). (Or do it like klynn47 suggests. Propably best OO..) /ulf Thanks klynn and Ulf. So, does that mean that, in general, an object isn't able to access info about the array in which it is contained? Jay > Thanks klynn and Ulf. So, does that mean that, in general, an object isn't > able to access info about the array in which it is contained? An object is never contained in an array (nor in any other object), only a reference to it is. And since an object doesn't have any notion of what references might be pointing to itself (unless specifically coded and used that way), it follows that the answer to your question is yes, that's what it means. (Whatever `it' was, which is hard to say since you didn't quote any context.) SignatureCheers, Tilman `Boy, life takes a long time to live...' -- Steven Wright >> Thanks klynn and Ulf. So, does that mean that, in general, an object >> isn't >> able to access info about the array in which it is contained? > > An object is never contained in an array (nor in any other object), > only a reference to it is. Of course, you're right. I should've used more careful language to prevent responses such as yours. > And since an object doesn't have any notion > of what references might be pointing to itself (unless specifically > coded and used that way), it follows that the answer to your question > is yes, that's what it means. Thanks, that answers my question. > (Whatever `it' was, which is hard to > say since you didn't quote any context.) Thought it was pretty apparent that, since I addressed both respondents, I was responding to the points made in both their posts... but no matter; you answered my question. Thanks. Jay [...] >> (Whatever `it' was, which is hard to >> say since you didn't quote any context.) > > Thought it was pretty apparent that, since I addressed both respondents, I > was responding to the points made in both their posts... Yes, but not everyone has the time to follow every thread very closely, or the incliniation to look up preceding posts in a thread just to get context. So by not quoting anything, you artificially limit the group of people who might usefully follow up to it. > but no matter; you answered my question. Thanks. You're very welcome. SignatureCheers, Tilman `Boy, life takes a long time to live...' -- Steven Wright > In message <421e5d2f$0$22518$2c56edd9@news.cablerocket.com>, > > Yes, but not everyone has the time to follow every thread very > closely, or the incliniation to look up preceding posts in a thread > just to get context. So by not quoting anything, you artificially > limit the group of people who might usefully follow up to it. I would respectfully suggest then that if one doesn't have the time to read a (short) thread, one should not post a response and then criticize another poster because one doesn't understand the context. Jay Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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