Java – 怎样将 Array 转为 Stream

╰半夏微凉° 2022-06-15 08:11 162阅读 0赞

在java 8中，您可以使用arrays.stream或Stream.of将 `Arrays` Array into a Stream.

## 1. Object Arrays ##

For object arrays, both `Arrays.stream` and `Stream.of` returns the same output.

TestJava8.java

package com.mkyong.java8; import java.util.Arrays; import java.util.stream.Stream; public class TestJava8 { public static void main(String[] args) { String[] array = { "a", "b", "c", "d", "e"}; //Arrays.stream Stream<String> stream1 = Arrays.stream(array); stream1.forEach(x -> System.out.println(x)); //Stream.of Stream<String> stream2 = Stream.of(array); stream2.forEach(x -> System.out.println(x)); } }

Output

a
    b
    c
    d
    e
    a
    b
    c
    d
    e

检查JDK源代码.

Arrays.java

/** * Returns a sequential {@link Stream} with the specified array as its * source. * * @param <T> The type of the array elements * @param array The array, assumed to be unmodified during use * @return a {@code Stream} for the array * @since 1.8 */ public static <T> Stream<T> stream(T[] array) { return stream(array, 0, array.length); }

Stream.java

/** * Returns a sequential ordered stream whose elements are the specified values. * * @param <T> the type of stream elements * @param values the elements of the new stream * @return the new stream */ @SafeVarargs @SuppressWarnings("varargs") // Creating a stream from an array is safe public static<T> Stream<T> of(T... values) { return Arrays.stream(values); }

注  
对象数组的stream.of方法调用arrays.stream内部。

## 2. 原始数组 ##

对原始数组, 用`Arrays.stream` 和`Stream.of` 将返回不同的输出结果.

TestJava8.java

package com.mkyong.java8; import java.util.Arrays; import java.util.stream.IntStream; import java.util.stream.Stream; public class TestJava8 { public static void main(String[] args) { int[] intArray = { 1, 2, 3, 4, 5}; // 1. Arrays.stream -> IntStream IntStream intStream1 = Arrays.stream(intArray); intStream1.forEach(x -> System.out.println(x)); // 2. Stream.of -> Stream<int[]> Stream<int[]> temp = Stream.of(intArray); // Cant print Stream<int[]> directly, convert / flat it to IntStream IntStream intStream2 = temp.flatMapToInt(x -> Arrays.stream(x)); intStream2.forEach(x -> System.out.println(x)); } }

Output

1
    2
    3
    4
    5
    1
    2
    3
    4
    5

Review the JDK source code.

Arrays.java

/** * Returns a sequential {@link IntStream} with the specified array as its * source. * * @param array the array, assumed to be unmodified during use * @return an {@code IntStream} for the array * @since 1.8 */ public static IntStream stream(int[] array) { return stream(array, 0, array.length); }

Stream.java

/** * Returns a sequential {@code Stream} containing a single element. * * @param t the single element * @param <T> the type of stream elements * @return a singleton sequential stream */ public static<T> Stream<T> of(T t) { return StreamSupport.stream(new Streams.StreamBuilderImpl<>(t), false); }

选择哪一个？  
对象的数组，都是调用同一个arrays.stream（参见例1，JDK源代码）。原始数组，我更喜欢arrays.stream为好，因为它返回固定大小的intstream，容易操作。

P.S Tested with Oracle JDK 1.8.0\_77

References

1.  [Arrays JavaDoc][]
2.  [Stream JavaDoc][]
3.  [How to print an array, java and java 8 examples][How to print an array_ java and java 8 examples]

[Arrays JavaDoc]: https://docs.oracle.com/javase/8/docs/api/java/util/Arrays.html
[Stream JavaDoc]: https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html
[How to print an array_ java and java 8 examples]: http://www.mkyong.com/java/java-how-to-print-an-array/