New characteristics of j2se5.0 generis

J2se








The following procedure is easy to understand, and it is easy to understand the generis feature by comparing two programs.



Oldlist.java







/**



* @author Roson



*



* 2005-4-11



*/



Package collection;







Import java.util.*;







public class Oldlist {







private void Testlist ()



{



List list=new ArrayList ();



List.add (New String ("helloworld!"));



List.add (New String ("goodbye!"));



List.add (New Integer (95));



Printlist (list);



}







private void Printlist (List list)



{



Iterator I=list.iterator ();



while (I.hasnext ())



{



String item= (String) i.next ();



System.out.println ("Item:" +item);



}



}







public static void Main (string[] args) {



Oldlist old=new oldlist ();



Old.testlist ();



}



}







Can be compiled, but will error when performing to the third print.



















Newlist.java







/**



* @author Roson



*



* 2005-4-11



*/



Package collection;







Import java.util.*;







public class NewList {







private void Testnew ()



{



List<string> list=new arraylist<string> ();



List.add (New String ("helloworld!"));



List.add (New String ("goodbye!"));



List.add (New Integer (95)); There's no extra plastic.



Printlist (list);



}







private void Printlist (List list)



{



Iterator<string> I=list.iterator ();



while (I.hasnext ())



{



String Item=i.next ();



System.out.println ("Item:" +item);



}



}



public static void Main (string[] args) {



NewList list=new newlist ();



List.testnew ();



}



}











If you add a comment here, you will not be able to compile it and not be wrong in the run-time times. It is helpful to check out errors in advance.















Oldloop.java







/**



* @author Roson



*



* 2005-4-11



*/



Package collection;







Import java.util.*;







public class Oldloop {







public static void Main (string[] args) {



List list=new ArrayList ();



List.add (New String ("helloworld!"));



List.add (New String ("goodbye!"));



For (iterator I=list.iterator (); I.hasnext ();)



{



String item= (String) i.next ();



System.out.println ("Item:" +item);



}



}



}











Newloop.java



/**



* @author Roson



*



* 2005-4-11



*/



Package collection;







Import java.util.*;







public class Newloop {







public static void Main (string[] args) {



List<string> list=new arraylist<string> ();



List.add (New String ("helloworld!"));



List.add (New String ("goodbye!"));



for (String str:list)//It's a lot simpler than it used to be.



{



System.out.println ("Item:" +str);



}



}



}



From the above two programs can be easily seen, the second is much simpler:







Discuss:



Here only take list as an example, of course there are other, such as Hashmaps,linklists and other collection.



There are a lot of improvements in j2se5.0, and there's not much to say. However, you can refer to the English document J2SE5 Nutshell and J2se5. At first, I still feel generis bad, but see the JBSS useful to also feel simple and then see the file, really very convenient oh. You may try!