Check if String Array contains a Substring without loop

Question

I want to find a substring in an array of strings, without using loop. I'm using:

import java.util.Arrays;

public class MyClass {
    public static void main(String args[]) {

        String[] files = new String[]{"Audit_20190204_061439.csv","anotherFile"};
        String substring= ".csv";

        if(!Arrays.stream(files).anyMatch(substring::contains)) {
            System.out.println("Not found:" + substring);
        }
    }
}

I'm always getting Not found. What is wrong with the approach?

You are just hiding the loop via the stream. That doesn't make the approach any better not faster than a straightforward, understandable, for loop. — Has QUIT--Anony-Mousse
– Has QUIT--Anony-Mousse, Commented Feb 4, 2019 at 9:11
On the contrary, see how the overuse of lambdas caused you to make a mistake that is hard to find (wrong parameter order in the substring function). — Has QUIT--Anony-Mousse
– Has QUIT--Anony-Mousse, Commented Feb 4, 2019 at 9:12

user5155835 · Accepted Answer · 2019-02-04 13:44:47Z

4

You are checking whether the String ".csv" does not contain any of the elements of your Stream, which is the opposite of what you wanted.

It should be:

if (!Arrays.stream(files).anyMatch(s -> s.contains(substring))) {
    System.out.println("Not found:" + substring);
}

P.S. As commented, you can use noneMatch instead of anyMatch, which will save the need to negate the condition:

if (Arrays.stream(files).noneMatch(s -> s.contains(substring))) {
    System.out.println("Not found:" + substring);
}

and if the ".csv" substring should only be searched for in the end of the String (i.e. treated as a suffix), you should use endsWith instead of contains.

edited Feb 4, 2019 at 13:44

user5155835

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answered Feb 4, 2019 at 7:25

Eran

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2 Comments

Lino Over a year ago

! + anyMatch() -> noneMatch()

Tim Biegeleisen Over a year ago

The OP probably wants to use String#endWith here, since .csv is an extension, should only appear at the end of the string.

Naman · Accepted Answer · 2019-02-04 07:29:26Z

2

You possibly need to check the file extension and can use endsWith for it instead and improve your condition to:

if (Arrays.stream(files).noneMatch(a -> a.endsWith(substring))) {
    System.out.println("Not found:" + substring);
}

answered Feb 4, 2019 at 7:29

Naman

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Comments

Tim Biegeleisen · Accepted Answer · 2019-02-04 07:36:32Z

1

I am not a streams guru, but I believe that you want something like this:

String[] files = new String[] { "Audit_20190204_061439.csv", "anotherFile" };

for (String file : files) {
    if (file.endsWith(".csv")) {
        System.out.println("found a CSV file");
    }
}

I use String#endsWith here because presumably .csv refers to a file extension, and should only register a hit if occur at the end of the filename.

We could also use String#matches here:

Pattern pattern = Pattern.compile(".*\\.csv$");
for (String file : files) {
    Matcher matcher = pattern.matcher(file);
    if (matcher.find()) {
        System.out.println("found a CSV file");
    }
}

edited Feb 4, 2019 at 7:36

answered Feb 4, 2019 at 7:29

Tim Biegeleisen

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2 Comments

Lino Over a year ago

I would recommend against file#matches() inside loops, better create a Pattern beforehand: Pattern.compile(".*.csv$")

Tim Biegeleisen Over a year ago

@Lino And in fact you have told me this before. I guess old habits die hard :-(

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