如何转换“流<string> " 到 "字符串"</string>

Question

I want to convert Stream<String> to String and print all the string.

Stream<String> result= Stream.of("do","re","ma","po","fa","si")
                             .filter(str -> str.length()>5)
                             .peek(System.out:: println);
                           //.allMatch(str -> str.length() >5);

System.out.println(result);

Here down output i get

java.util.Spliterators$1Adapter@63961c42

The result is printing an object but not a String and while converting to toString() also printing the same but how to print as a String

Answer 1

In java 8, there is method joining() , Which is the part of Collectors class . You have to join this string using Collectors.joining() .

Here down is code:

String result = Stream.of("do", "re", "ma", "po", "fa", "si")
                .filter(str -> str.length() > 1)
                .collect(Collectors.joining());

Or

String result= Stream.of("do","re","ma","po","fa","si")
                .filter(str -> str.length() > 1)
                .peek(System.out::println)
                .collect(Collectors.joining());

Answer 2

Do you looking for something like this?

    String result = Stream.of("do","re","ma","po","fa","si").
                collect(Collectors.joining(""));
    System.out.println(result);

Output:

doremapofasi

Or:

        String result = Stream.of("do", "re", "ma", "po", "fa", "si")
            .filter(str -> str.length() > 1)
            .peek(System.out::println)
            .collect(Collectors.joining(""));
        System.out.println(result);

Output:

do
re
ma
po
fa
si
doremapofasi

Answer 3

You misunderstand the mechanisms behind the Stream API .

A stream pipeline consists of a source (which might be an array, a collection, a generator function, an I/O channel, etc), zero or more intermediate operations (which transform a stream into another stream, such as filter(Predicate)), and a terminal operation (which produces a result or side-effect, such as count() or forEach(Consumer)). Streams are lazy ; computation on the source data is only performed when the terminal operation is initiated , and source elements are consumed only as needed.

The main conclusion:

Operations on the data in the pipeline will be performed only if the terminal operation is initiated .

Stream without a terminal operation is perfectly valid from the compiler's perspective of view. It will compile, but it'll not be executed.

And what you have tried to print ( java.util.Spliterators$1Adapter@63961c42 ) isn't a result, but the stream object itself.

To produce a result or side-effect Stream-pipeline must end with a terminal operation ( collect() , reduce() , count() , forEach() , findFirst() , findAny , anyMatch() - which commented out in your code). Note, that peek() is an intermediate operation and confuse it with forEach() . You can use peek() as many time as need, which can be useful for debugging purposes.

    public static void main(String[] args) {

        String result = getStream()
                .filter(str -> str.length() > 5 && str.length() < 8)
                .findFirst() // that will produce a single result that may or may not be present
                .orElseThrow(); // action for the case if result is not present

        System.out.println("Single result: " + result + "\n");

        getStream()
                .filter(str -> str.contains("a"))
                .peek(System.out::println) // intermediate operation that will print every element that matches the first filter
                .filter(str -> str.length() > 8)
                .forEach(System.out::println); // terminal operation that prints every element remained after processing the pipeline
    }

    private static Stream<String> getStream() {
        return Stream.of("Ignoranti", "quem", "portum", "petat", "nullus", "suus", "ventus", "est");
    }

output

Single result: portum

Ignoranti
Ignoranti
petat

Answer 4

If you really only want to only print the elements rather than getting them in return, you can just

Stream.of("do","re","ma","po","fa","si")
    .filter(str -> str.length()>5)
    .forEach(System.out:: println);

forEach is also a "terminating" operation on the stream, which means that it "actually executes" it.

Answer 5

you need to 'execute' the stream by calling collect or reduce

assertEquals("ab", Arrays.stream(new String[]{"a", "b"}).reduce("", (s,x) -> s + x));