• 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 ...
  • Liutauras Vilda
  • Campbell Ritchie
  • Tim Cooke
  • Bear Bibeault
  • Devaka Cooray
  • Jeanne Boyarsky
  • Knute Snortum
  • Junilu Lacar
Saloon Keepers:
  • Tim Moores
  • Ganesh Patekar
  • Stephan van Hulst
  • Pete Letkeman
  • Carey Brown
  • Tim Holloway
  • Ron McLeod
  • Vijitha Kumara

toArray(arr[])  RSS feed

Ranch Hand
Posts: 278
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator
I have a doubt with the concept of Collection.toArray() method
1.I could really get the difference between
toArray() and toArray(arr[])
In ,my code snippet , even after using toarray(some array) syntax ,i have to explicitly cast my Object array to String ,otherwsie ClassCastException comes .

hashset = is some HashSet Collection having Strings
//Converting HashSet to objectArray for Sorting elements
String obj[]=(String [])hashset.toArray(new String[2]);

Object obj1[]=hashset.toArray();
//Sorting string array
(instanceof Sidekick)
Ranch Hand
Posts: 8791
  • Mark post as helpful
  • send pies
  • Quote
  • Report post to moderator

String obj[]=(String [])hashset.toArray(new String[2]);

Yes, you still have to cast the results of toArray to String[]. The toArray method here well and truly does return a String[] but the compiler can't know that. The compiler only knows the signature of toArray which promises to return Object[]. Here you have the confidence to tell the JVM at runtime to do the cast.

Have you looked into Generics in Java 5 and later? They allow us to eliminate some, but not all, cast operations like this.

Now we've told the compiler that the set will only contain Strings and the compiler enforces that rule so it knows that toArray will return String[].
[ June 16, 2007: Message edited by: Stan James ]
  • Post Reply Bookmark Topic Watch Topic
  • New Topic
Boost this thread!