Return Not-Hidden Files

Question

Prior to Java 8, this method would be used to create a list of hidden files:

    File[] hiddenFiles = new File("./directory/").listFiles(new FileFilter() {
        public boolean accept(File file) {
            return file.isHidden();
        }
    });

In Java 8, this can be shortened to:

File[] hiddenFiles = new File("./directory/").listFiles(File::isHidden);

Returning non-hidden files in the original code was a trivial change: return file.!isHidden(); as a substitute for return file.isHidden();. I cannot recreate this functionality within a single line.

There is no isNotHidden function within the File class. Without creating one (or without deferring to the original, more verbose code), is there a way to recreate it using the new single-line style?

You can use `listFiles(f -> !f.isHidden())`. You can't negate a method reference. — daniu, Aug 08 '18 at 15:11
**"Returning non-hidden files in the original code was a trivial change: `return file.!isHidden();`"** Not that trivial apparently, because that's not valid syntax. ;) — Michael, Aug 08 '18 at 15:26
@daniu you can do via `Predicate.not(File::isHidden)` in java-11 — Eugene, Aug 08 '18 at 15:44
Here's the original bug: https://bugs.openjdk.java.net/browse/JDK-8050818 — Ravindra Ranwala, Aug 08 '18 at 16:32
@Michael: Hah, oops. Maybe I should start copying code in from my IDE rather than trying to remember it! It does look like that other answer hits mine though, thanks for that. — MK_Codes, Aug 09 '18 at 07:29
@Eugene for completeness sake: you can also negate the predicate itself in Java 8 if you assign it first: `Predicate notHidden = File::isHidden; notHidden = notHidden.negate();` — daniu, Aug 13 '18 at 05:52
@daniu or even `((Predicate)File::isHidden).negate()`, but neither is as nice as the java-11 one — Eugene, Aug 13 '18 at 07:56

Ravindra Ranwala · Accepted Answer · 2018-08-08T15:35:10.233

3

How about this,

File[] hiddenFiles = new File("c:/data").listFiles(f -> !f.isHidden());

edited Aug 08 '18 at 15:35

answered Aug 08 '18 at 15:11

Ravindra Ranwala

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score 3 · Answer 2 · answered Aug 08 '18 at 15:41

3

Coming in java-11 Predicate.not, until then you can't via a method reference

Predicate.not(File::isHidden)

answered Aug 08 '18 at 15:41

Eugene

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Return Not-Hidden Files

2 Answers2