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why the output is classcastexception ?

 
Greenhorn
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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
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Person is not comparable: if you change to this, all works

 
Ranch Hand
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TreeSet is a container which put objects in sorted order.
In order to sort data , object being added should be of type Comparable .
In class Person implements Comparable interface and implements its method.
When you add any new object , this method will be called for comparison .
 
Ranch Hand
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This code will compile and run without exceptions:

import java.util.*;
public class Test1{
public static void main(String a[]){
Set s = new HashSet(); <--- guess why
s.add(new Person(20));
s.add(new Person(10));
System.out.println(s);
}
}
class Person{
Person(int i){}
}
[ November 13, 2007: Message edited by: Andry Dub ]
 
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