private final String[] okFileExtensions = new String[] { "csv" };
Would someone please explain why {}
is written after a String array declaration?
Thanks.
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).
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"};
Creating an array of strings
inline.
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