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joining

joining()​

joining() is a static method of Collectors that returns a Collector that concatenates the input elements with the specified delimiter. There are three variations of the joining() method:

Example​

streamJoining()​

    public void streamJoining() {
        List<String> stringList = Arrays.asList("zjc", "streams", "collectors");
        System.out.println("Stream before modification - " + stringList);

        Stream<String> stringStream = stringList.stream();
        // concat the elements of the list using the joining method
        String concatenatedString = stringStream.map(String::toUpperCase).collect(Collectors.joining());

        // result after the concatenation
        System.out.println(concatenatedString);
    }

output​

ZJCSTREAMSCOLLECTORS

joining(CharSequence delimiter)​

Example​

streamJoiningDelimiter()​

    public void streamJoiningDelimiter() {
        List<String> stringList = Arrays.asList("zjc", "streams", "collectors");
        System.out.println("Stream before modification - " + stringList);

        Stream<String> stringStream = stringList.stream();
        // delimiter to use
        String delimiter = "-";
        // concat the elements of the list using the joining method
        String concatenatedString = stringStream.map(String::toUpperCase).collect(Collectors.joining(delimiter));

        // result after the concatenation
        System.out.println(concatenatedString);
    }

output​

ZJC-STREAMS-COLLECTORS

joining(CharSequence delimiter, CharSequence prefix, CharSequence suffix)​

Example​

streamJoiningDelimiterChars()​

    public void streamJoiningDelimiterChars() {
        List<String> stringList = Arrays.asList("zjc", "streams", "collectors");
        System.out.println("Stream before modification - " + stringList);

        Stream<String> stringStream = stringList.stream();

        // delimiter to use
        String delimiter = "-";

        // prefix to use
        String prefix = "prefix-";

        // suffix to use
        String suffix = "-suffix";

        // concat the elements of the list using the joining method
        String concatenatedString = stringStream.map(String::toUpperCase).collect(Collectors.joining(delimiter, prefix, suffix));

        // result after the concatenation
        System.out.println(concatenatedString);
    }

output​

prefix-ZJC-STREAMS-COLLECTORS-suffix