generic and arrays

[Tian Zhang]

hello!

could someone suggest what a solution for the following code would be?

public class foo<MyType>{
   MyType[] myTypeArray = null;
 
   public foo(){
      myTypeArray = new MyType[10];
   }
}

at the moment i have to up cast everything to Object as the above is illegal:

public class foo<MyType>{
   Object[] myTypeArray = null;
 
   public foo(){
      myTypeArray = new Object[10];
   }
}

this creates a problem as if i wanted to iterate through the array using the new syntax:

for(MyType i : myTypeArray){}

becomes illegal.

thanks,
tian

[marc weber]

See if this helps.

[Tian Zhang]

hello,

thanks for the link, though unfortunatly i didnt find it that useful i'm sure it will be useful to others!

i've ended up with some ugly casting as googling: generic arrays by luck landed me on page that comfirmed what i had suspected in the first post.

thanks,
tian

[Jim Yingst]

One option is to not use arrays at all, and use List<MyType> instead. Another, if you really really need arrays of the appropriate type, is to have your instance keep a reference to the Class it's associated with (require it in the constructor or factory method). Then use java.lang.reflect.Array.newInstance(clss, size) to create the appropriate array.

[Tony Morris]

Originally posted by Tian Zhang:
hello!

could someone suggest what a solution for the following code would be?

public class foo<MyType>{
   MyType[] myTypeArray = null;
 
   public foo(){
      myTypeArray = new MyType[10];
   }
}

at the moment i have to up cast everything to Object as the above is illegal:

public class foo<MyType>{
   Object[] myTypeArray = null;
 
   public foo(){
      myTypeArray = new Object[10];
   }
}

this creates a problem as if i wanted to iterate through the array using the new syntax:

for(MyType i : myTypeArray){}

becomes illegal.

thanks,
tian

You have found (one of many limitations) a limitation of generics. You'll find evidence of your best case scenario in places such as the source to java.util.ArrayList or net.tmorris.adt.set.MutableSet, which amounts to a compile-time warning (or alternatively, something other than an array without O(1) seek).

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