private final String[] okFileExtensions = new String[] { "csv" };
Would someone please explain why {} is written after a String array declaration?
Thanks.
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1Consider using an enumeration, instead of explicitly hardcoding the file extensions.Dave Jarvis– Dave Jarvis2010-01-11 17:01:26 +00:00Commented Jan 11, 2010 at 17:01
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4 Answers
It's an array of one element. In this case containing the String "csv".
When written as part of a declaration, this can be written in a more concise form:
private final String[] okFileExtensions = { "csv" };
Multiple-element arrays use commas between values. There needn't be any values at all.
private final String[] okFileExtensions = { "csv", "tsv" };
private final String[] noFileExtensions = { };
It may be worth noting that although the reference is final the array is not. So you can write:
okFileExtensions[0] = "exe";
A way to get around this is to switch to collections and use an unmodifiable implementation:
private final Set<String> okFileExtensions = Collections.unmodifiableSet(
new HashSet<String>(Arrays.asList({
"csv"
}));
JDK8 is intended to have enhancement to collections that will make this more concise. Probably List and Set literals within the language. Possibly:
private final Set<String> okFileExtensions = { "csv" };
Collections should generally be preferred over arrays (for reference types).
answered Jan 11, 2010 at 15:57
Tom Hawtin - tackline
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4 Comments
TabbyCool
If you wanted to add multiple file extension values to the array you would just separate them with commas eg. private final String[] okFileExtensions = { "csv", "txt", "sql" };
Tom Hawtin - tackline
I have now added that to my answer.
rsp
Collections should generally be preferred over arrays (for reference types) that depends largely on what the purpose and scope of the array is. As given here this is much too general for my taste.
BalusC
+1 for mentioning the JDK7 enhancement. Didn't knew that particular one. Looks very useful.
That's the Java's valid syntax for array declaration.
You may use that when you are passing an array without declaring a variable:
public void printArray( String [] someArray ) {
for( String s : someArray) {
System.out.println( s );
}
}
And invoke it like this:
printArray( new String [] { "These", "are", "the", "contents"} );
The curly braces can only be used when declaring the array so the following is not allowed:
Stirng [] a;
a = {"on", "two"};
Comments
Creating an array of strings inline.
Comments
I think a less verbose (also confusing) declaration would have been :
private final String[] okFileExtensions = {"csv"};
1 Comment
Stephen C
Maybe ... but the
new <type>[] {...} syntax can do more.