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warning: [unchecked] unchecked method invocation  RSS feed

 
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Hi guys. Apologies if this should be obvious. When I compile the following -Xlint I'm warned:

CompareMe.java:27: warning: [unchecked] unchecked method invocation: <T>sort(java.util.List<T> ;) in java.util.Collections is applied to (java.util.List<scratch.Item> ;)
Collections.sort(list);
^
1 warning

list is declared to hold only <Items>, and I assume Collections.sort is a generic method. What am I missing?

Thanks much.


[ June 18, 2008: Message edited by: Mike Mitchell ]
 
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You need to make Item implement Comparable<Item>, not just Comparable (which is a raw type). That is:
 
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public int compareTo(Object o) { Item i = (Item) o; if (this.number < i.number) { return -1; } else if (this.number > i.number) { return 1; } else { return 0; } }



Hi

compareTo() method's signature must be the same, as you are overriding it and not overloading. That means, you are implementing the method from the interface Comparable.

public int compareTo(Object o) {
Item i = (Item) o;
if (this.number < i.number) {
return -1;
} else if (this.number > i.number) {
return 1;
} else {
return 0;
} }

and not

public int compareTo(Item o) {
Item i = (Item) o;
if (this.number < i.number) {
return -1;
} else if (this.number > i.number) {
return 1;
} else {
return 0;
} }

Kind Regards
Kris
 
Mike Mitchell
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Thanks much Matt and Kris -- that got me straightened out.
 
It is sorta covered in the JavaRanch Style Guide.
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