• Post Reply Bookmark Topic Watch Topic
  • New Topic
programming forums Java Mobile Certification Databases Caching Books Engineering Micro Controllers OS Languages Paradigms IDEs Build Tools Frameworks Application Servers Open Source This Site Careers Other all forums
this forum made possible by our volunteer staff, including ...
Marshals:
  • Campbell Ritchie
  • Ron McLeod
  • Paul Clapham
  • Bear Bibeault
  • Junilu Lacar
Sheriffs:
  • Jeanne Boyarsky
  • Tim Cooke
  • Henry Wong
Saloon Keepers:
  • Tim Moores
  • Stephan van Hulst
  • Tim Holloway
  • salvin francis
  • Frits Walraven
Bartenders:
  • Scott Selikoff
  • Piet Souris
  • Carey Brown

why ClasscastException????

 
Ranch Hand
Posts: 481
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
why ClasscastException??? do explain me clearly

i didnot get it

import java.util.*;
public class test1{
public static void main(String a[]){
Set s = new TreeSet();
s.add(new Person(20));
s.add(new Person(10));
System.out.println(s);
}
}
class Person{
Person(int i){}
}
 
Ranch Hand
Posts: 40
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
TreeSet implements SortedSet. When elements are added to the TreeSet collection it has to compare the to-be-added object against the existing collection elements. So either the to-be-added object has to implement comparable or a comparator has to be provided during TreeSet creation. If u try to add only one element u wont get this exception.

Try this and hope this is of some use.

import java.util.*;
public class SetTest{
public static void main(String a[]){
Set s = new TreeSet();
s.add(new Person(20));
s.add(new Person(10));
s.add(new Person(20));
System.out.println(s);
}
}
class Person implements Comparable
{
int i=0;
Person(int i){this.i=i;}
public int compareTo(Object o)
{
if ((o instanceof Person) && (((Person)o).i==i))
return 0;
else
return 1; // not equal
}
}
 
Ranch Hand
Posts: 1277
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
you wont see such questions in the 1.4 exam
 
Yeah, but how did the squirrel get in there? Was it because of the tiny ad?
the value of filler advertising in 2020
https://coderanch.com/t/730886/filler-advertising
    Bookmark Topic Watch Topic
  • New Topic