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Doubt in Generics...  RSS feed

 
Ranch Hand
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1)
import java.util.*;
public class gen{
public static void main(String[] str){
List<? extends Number> list1 = new ArrayList<Integer>();
}
}


Number Is Super Class For Integer..Why This Code Shows Compile Error...


2)
import java.util.*;
class animal{
}
class dog extends animal{
}

class test{
public static void main(String[] str){
List<? extends animal> lst = new ArrayList<dog>();
}

}


But This Second Code Is Not Showing Compile Error
 
Ranch Hand
Posts: 893
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With your first and second code I don't get a compile error. What is your fault message?
 
Ranch Hand
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nothing wrong with 1) or 2)
 
Greenhorn
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I compiled both codes with eclipse; they were fine.
 
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No compiler errors
 
Sheriff
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thangraj please tell the error that you are receiving as there is no compilation error as everyone is saying...You may have posted incomplete code... If you try to add any element to this list, then it will give you an error...
 
Thangaraj Selvamani
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Sorry to late Reply... The Error Which Im getting is

C:\SCJP>javac gen.java
gen.java:4: incompatible types
found : java.util.ArrayList<Integer>
required: java.util.List<? extends java.lang.Number>
List<? extends Number> list1 = new ArrayList<Integer>();
^
1 error
C:\SCJP>java -version
java version "1.5.0-beta2"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-beta2-b51)
Java HotSpot(TM) Client VM (build 1.5.0-beta2-b51, mixed mode, sharing)

Please Tell Me Why This Error Comes For First Program.... But Second Program Is Working Correctly...Does Any Thing Problem With Version...

[ November 04, 2008: Message edited by: Thangaraj Raj ]
[ November 04, 2008: Message edited by: Thangaraj Raj ]
 
Remko Strating
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Try a different java version. I use 1.6.0.7.
 
Thangaraj Selvamani
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Im Preparing For Java5(Scjp)..... But According To That It Must Not Give Compilation error??...
 
Ankit Garg
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thangraj did you create any class of your own with the name Integer??? Also the version of your JDK is Beta. So try a newer version...
 
Thangaraj Selvamani
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Ankit Garg...I have Not Created Integer Class..Ya I Tried In Other Version...its working...Correctly...What Will Be The Reason Not To Work In JDK1.5(Beta)...
 
Ankit Garg
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well Beta is a testing stage of a software's life cycle. There are bugs in software at Beta stage (there are bugs in final softwares too ). So it must be a bug...
 
Thangaraj Selvamani
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Thanks Ankit Garg.. To Cleare My Doubt...
 
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