thanks for the idea, it seems to work. about Integer class, I haven't been able to add it to the tree. I guess for the time being this homework will have to wait.
----- Original Message ----- From: Hallgrímur Njálsson To: [email protected] Sent: Saturday, September 12, 2009 3:54 PM Subject: Re: [java programming] Java Collections Framework - lab 1008; TreeSet I have figured out this part of the homework... You have to write your "MyOwnClass" so it implements Comparable I did it like this... class MyOwnClass extends Object implements Comparable { . . . Then you have to implement the method compareTo so it can compare MyOwnClass object to the calling object I include my compareTo method... public int compareTo(Object o) { return (this.toString().compareTo(o.toString())); } Hope this will help you. I am still having problem comparing the Integer object to the String and MyOwnClass Objects... Have you figured that out yet? My regards -Halli 2009/9/12 Deyan Pavlov <[email protected]> if you mean: TreeSet<Object> ts = new TreeSet<Object>(); ts.add("one") ; ts.add("two") ; MyOwnClass obj1 = new MyOwnClass( ); ts.add(obj1) ; this still has the same error ClassCastException Maybe another idea? ----- Original Message ----- From: Zahari Palazov To: [email protected] Cc: [email protected] Sent: Friday, September 11, 2009 7:26 PM Subject: Re: [java programming] Re: Java Collections Framework - lab 1008; TreeSet TreeSet<Object> ts = new TreeSet<Object>(); try with this On Fri, Sep 11, 2009 at 6:48 PM, Deyan Pavlov <[email protected]> wrote: Hi, I understand Treeset is a collection of elements that are comparable. But the homework is to put in this collection String, Integer and MyOwnClass objects, so three very different types. I think that so far there hasn't been any idea in previous lessons about how to put all these things together in one group. So far I have solved all homeworks completely on my own but now this seems to be a bit out of boundary exception for me. Any practical idea how to put these objects together? Thanks in advance!! ----- Original Message ----- From: "Ashok A V" <[email protected]> To: <[email protected]> Cc: "Free Java Programming Online Training Course By Sang Shin" <[email protected]> Sent: Friday, September 11, 2009 9:45 AM Subject: Re: [java programming] Java Collections Framework - lab 1008; TreeSet Hi , TreeSet is the Set which actually sorts your added items. So now the confusion happens when you add objects of different types. Say first you add two Strings : ts.add("one") ; ts.add("two") ; Then you add three Integers : ts.add(new Integer(1)) ; ts.add(new Integer(2)) ; ts.add(new Integer(3)) ; And finally you add MyOwnClass object to the set MyOwnClass obj1 = new MyOwnClass( ); ts.add(obj1) ; Now remember Tree Set is a collection that sorts the objects in your Set collection. public TreeSet() Constructs a new, empty set, sorted according to the elements' natural order. All elements inserted into the set must implement the Comparable interface. Furthermore, all such elements must be mutually comparable: e1.compareTo(e2) must not throw a ClassCastException for any elements e1 and e2 in the set. If the user attempts to add an element to the set that violates this constraint (for example, the user attempts to add a string element to a set whose elements are integers), the add(Object) call will throw a ClassCastException. So if you added only string then String Class implements Comparable interface which has a compareTo() method. So Sorting of strings is possible.The problem occurs when it comes to the integer objects , the string class is not able to cast it and it fails saying that : Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Integer So if you plan to use TreeSet see to that you add the same kind of objects which are sortable by a compareTo() method For more reading : http://java.sun.com/j2se/1.4.2/docs/api/java/util/TreeSet.html Thanks, Ashok A V On Fri, Sep 11, 2009 at 1:17 AM, Deyan Pavlov <[email protected]> wrote: > Lab 1008, 2.4 homework - TreeSet iterator: > > import java.util.TreeSet; > import java.util.Iterator; > import java.util.*; > > public class Main { > > > public static void main(String[] args) { > // TODO code application logic here > TreeSet ts = new TreeSet(); > ts.add("one") ; > ts.add("two") ; > > // HERE comes the problem, trying to add the Integer(1), (2) and (3) > > ts.add(new Integer(1)) ; > ts.add(new Integer(2)) ; > ts.add(new Integer(3)) ; > > MyOwnClass obj1 = new MyOwnClass( ); > ts.add(obj1) ; > > } > } > Result is: > Exception in thread "main" java.lang.ClassCastException: java.lang.String > cannot be cast to java.lang.Integer > at java.lang.Integer.compareTo(Integer.java:35) > at java.util.TreeMap.put(TreeMap.java:545) > at java.util.TreeSet.add(TreeSet.java:238) > at mytreeset.Main.main(Main.java:21) > Java Result: 1 > ------------------------------------------------------------------------------------------- > > MyOwnClass obj1 = new MyOwnClass( ); > ts.add(obj1) ; > > If I add the two rows above, adding the MyOwnClass obj1, which is properly > created in another file, > then comes an even longer list of errors that didn't happen when applying > this same method ADD() in LinkedList, ArrayList and HashSet > > Exception in thread "main" java.lang.NoClassDefFoundError: > mytreeset/MyOwnClass > at mytreeset.Main.main(Main.java:16) > Caused by: java.lang.ClassNotFoundException: mytreeset.MyOwnClass > at java.net.URLClassLoader$1.run(URLClassLoader.java:200) > at java.security.AccessController.doPrivileged(Native Method) > at java.net.URLClassLoader.findClass(URLClassLoader.java:188) > at java.lang.ClassLoader.loadClass(ClassLoader.java:307) > at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) > at java.lang.ClassLoader.loadClass(ClassLoader.java:252) > at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320) > > > Why can't I add objects to the TreeSet, while I could add them with not > exceptions in the case of LinkedList, ArrayList and HashSet ? > > Thank you!! > > > -- Victory belongs to the most persevering. - Napoleon --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/javaprogrammingwithpassion?hl=en -~----------~----~----~----~------~----~------~--~---
