HI,
Is it possible to do the homework like this:
ts.add(new Integer(1).toString());
Not sure whether it is agree to the homeworks expectation of "Add Integer
Object".
Thanks & Regards,
Hiran
On Sat, Sep 12, 2009 at 7:28 PM, Deyan Pavlov <[email protected]>wrote:
> *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 <[email protected]>
> *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 <[email protected]>
>> *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
>>> >>>
>>>
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