generics...

[Preethi Dev]

Hi ,i am just trying to understand the concept of generics and this is my own.


import java.util.*;
class card
{

public static void main(String args[])
{

card[] pair=new card<?,?>[10];
pair[0]=new card<Long,Long>(0L,0L);
pair[1]=new card<String,String>("","");
pair[2]=new card<String>("");

}
}
here i am getting compiler errors as "type card does not take parameters for each line in the main method".
should i create constructor for card?
if so how can i create it for unbounded wildcard parameterized type?

please clear this...

Thanks
Preetha

[Chandra Bhatt]

Hi Preetha,

What do you want to achieve here?
Generic array creation is not allowed.

[Punit Singh]

import java.util.*;
public class card<T,E>
{

public card(T obj1, E obj2){

}

public card(T obj1){

}
public static void main(String args[])
{

card[] pair=new card[10];
pair[0]=new card<Long,Long>(0L,0L);
pair[1]=new card<String,String>("","");

}
}

You have to make generic card class.
[ December 07, 2008: Message edited by: Punit Singh ]

[Preethi Dev]

Hi Chandra,
It is allowed to create an array whose component type is an unbounded wildcard parameterized type.
just go through this www.angelikalanger.com

Thanks
Preetha

[Deepak Jain]

Yes you should
Two Fixes:
Non Generic Code:

  
class Card<T, E> {
 
public Card(long l, int i) {
// TODO Auto-generated constructor stub
}
 
public Card(String string, String string2) {
// TODO Auto-generated constructor stub
}
 

}
 
public class GenericTest {
public static void main(String args[]) {
Card[] pair = new Card<?,?>[10];
pair[0] = new Card<Long, Integer>(0L, 0);
pair[1] = new Card<String, String>("", "");
}
}
 
  

Generic Code: This shows generics are power full

   
 
class Card<T, E> {
 
public Card(T obj1, E obj2) {
 
}
 
public Card(T obj1) {
 
}
}
 
public class GenericTest {
public static void main(String args[]) {
Card[] pair = new Card<?,?>[10];
pair[0] = new Card<Long, Integer>(0L, 0);
pair[1] = new Card<String, String>("", "");
}
}
 
 

Card[] pair = new Card<?,?>[10];
This line says that the array pair can take objects of any type . Since we have ? ? [2 ?] this implies that the objects must have a constructor that can take 2 arguments.

[Preethi Dev]

Thanks Deepak,

i tried with constructor it works.

Preetha