Re: unsafe or unchecked operations
dvd.regal@gmail.com wrote:
Of course, I might be guilty of looking for the 'easy' button and
Clearly you are.
maybe I should sit down for a week of studying generics in Java. But
Clearly you should.
really, there is not much ROI when all I wanted to change was a
cosmetic text in the program someone else wrote back in JDK 1.4 and
not any logic of the program.
Yet you use generics anyway, then complain that you don't understand them, but
refuse to study them.
Things I tried:
1. Tried more recent example file ExampleFileView.java but get the
same warning
2. Tried casting similar to example above from Knute J but get
warning.
Question:
But how does casting happen when 'filters != null'?
Example from above:
Hastable<String,CustomFileFilter> filters =
It is better to copy and paste than to type with typographic errors.
Hashtable is old, ten years obsolete - use HashMap, and declare the variable Map.
new Hashtable<String,CustomFileFiler>(5);
This implies you won't want to hold more than three entries in the Map.
Applying to file ExampleFileFilter.java:
Was:
/**
* Creates a file filter.
*/
public ExampleFileFilter() {
this.filters = new Hashtable();
Mixing raw types and generics is always trouble. You should have made this an
SSCCE.
}
/**
* Adds a filetype "dot" extension to filter against.
*/
public void addExtension(String extension) {
if(filters == null) {
filters = new Hashtable(5);
Again with the raw types.
}
filters.put(extension.toLowerCase(), this);
fullDescription = null;
}
Tried:
public ExampleFileFilter() {
this.filters = new Hashtable<String,ExampleFileFilter>();
} // DR: I think the 'this.filters' needs to be casted as well.
The past participle of "cast" is "cast".
If 'filters' is declared as you stated, as
'Hashtable<String,CustomFileFiler>', then you cannot assign it a
'Hashtable<String,ExampleFileFilter>' - one is not a subtype of the other.
public void addExtension(String extension) {
if(filters == null) {
Hashtable<String,ExampleFileFilter> filters = new
Hashtable<String,ExampleFileFilter>(5);
This variable 'filters' is a different variable than the one in the '== null'
clause. The one inside the 'if' block hides the instance variable (assuming
it was an instance variable - impossible to tell without an SSCCE).
} // DR: How does casting happen when 'filters != null'?
filters.put(extension.toLowerCase(), this);
If 'filters' is declared as you stated, as 'Hashtable<String,
CustomFileFiler>' [sic], then you cannot put into it a pair of '<String,
ExampleFileFilter>' unless 'ExampleFileFilter' is a subtype of
'CustomFileFiler' [sic]. Even then, you lose the information that the value
is a 'ExampleFileFilter', as your 'Hastable' [sic] only holds the information
told it.
fullDescription = null;
}
Maybe it's the 'put' method. I learned about warning suppression and
No, it's your other errors, that mostly have nothing to do with generics.
generics. Couldn't apply because I have little knowledge on how to
'generify' the 'put' method. I briefly considered digging into
finding the method 'put' but really sounded like a bad idea and not
much ROI compared with the alternatives (see 'What I did').
There would be a huge "ROI" on fixing your errors, though.
What I did:
1. Ignored the JDK 1.6 warning
2. Found out the JRE on the server is still at 1.4
3. Went back to compiling in JDK 1.4 with no warning
No warning, but not without error.
--
Lew