Applying regex to Java8 List<String>

Question

I have an array list

List<String> items = Arrays.asList("date=2017-01-10", "date=2017-02-10");

I want to convert this list and have quotes for each item in the list so date=2017-01-10 can be converted to date='2017-01-10'

List<String> items = Arrays.asList("date='2017-01-10'", "date='2017-02-10'");

How can i do in Java 8 ?

UPDATE: I want to use regex to achieve this.

To do it in Java 8, try first doing it in Java 7 with regex, and then... leave it as is, because Java8 doesn't bring anything new to this table other than minor quality of life improvements. — M. Prokhorov
– M. Prokhorov, Commented Aug 15, 2017 at 10:13
@Clijsters, the definition of "quality of life improvement" for this task. There's nothing you can achieve with Stream that you couldn't achieve with Java7-style code. — M. Prokhorov
– M. Prokhorov, Commented Aug 15, 2017 at 10:28
Sure, I'd however tell it bad style, not use java8-style code in a java-8 code environment. — Clijsters
– Clijsters, Commented Aug 15, 2017 at 10:30
@Clijsters, The bad style in my opinion is trying to shoe-horn lambdas and streams literally everywhere, regardless of how they look and behave. For example, a Stream creates way more garbage than side-effectful forEach, and the actual for-each Java7-style creates almost no garbage. — M. Prokhorov
– M. Prokhorov, Commented Aug 15, 2017 at 10:34

Youcef LAIDANI · Accepted Answer · 2017-08-15 10:21:55Z

3

You can use replaceAll with this regex ^(.*?)=(.*?)$ which return two groups one before the = the second after, so you can replace the input with group 1 $1 followed by =' then group 2 between two quotes '$2':

List<String> items = Arrays.asList("date=2017-01-10", "date=2017-02-10");
items = items.stream()
        .map(t -> t.replaceAll("(.*?)=(.*?)$", "$1='$2'"))
        .collect(Collectors.toList());

items.forEach(System.out::println);

Outputs

date='2017-01-10'
date='2017-02-10'

answered Aug 15, 2017 at 10:21

Youcef LAIDANI

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Comments

holi-java · Accepted Answer · 2017-08-15 10:20:06Z

I have seen your profile, I found you start to Java. so I'll give you the answer just for learning purpose.

use lookbehind to skip replacement. e.g: (?<==)
use group to capture the matched result in group, e.g: (.+)

use $ sign to references to captured group, e.g: $1.

List<String> result = items.stream()
//                                 match `=`            ---v
                           .map(it -> it.replaceFirst("(?<==)(.+)", "'$1'"))
//                     capture the rest substring in group  ---^
                           .collect(Collectors.toList());

You also can simply to use String#substring to achieve your way. for example:

int prefix = "date=".length();
List<String> result =items.stream()
                          .map(it->String.format("date='%s'",it.substring(prefix)))
                          .collect(Collectors.toList());

marvel308 · Accepted Answer · 2017-08-15 10:05:37Z

0

you can use the following code

    List<String> items = Arrays.asList("date=2017-01-10", "date=2017-02-10"), result = new ArrayList<String>();
    for(String item : items){
        item = item.replace("date=", "date='");
        item = item + "'";
        result.add(item);
    }
    for(String item : result){
        System.out.println(item);
    }

demo

answered Aug 15, 2017 at 10:05

marvel308

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