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Java Primitive Type Stream Boxed - Java 147

Java Primitive Type Stream Boxed – Java 147

Java Primitive Type Stream Boxed

提供 Primitive Stream 轉換成 Object Stream ，支援 Stream 排序、並行處理、聚合操作等，可以避免大量不必要的物件建立，節省系統資源，本篇增加了範例，並透過單元測試來驗證產出結果。

檔案目錄

./
   +- src
       +- test
       |   +- org
       |       +- ruoxue
       |           +- java_147
       |               +- stream
       |                   +- PrimitiveStreamBoxedTest.java

單元測試

Primitive Type Streams API 是 Java 8 中增加的特性之一，允許通過提供聲明性 API 來方便且更有效地處理集合和其他元素序列。

intStreamBoxed

建立一個 IntStream，增加三個元素，使用 boxed 轉成 Object Stream ，內有三個元素。

	@Test
	public void intStreamBoxed() {
		int expectedCount = 3;
		IntStream stream = IntStream.of(1, 2, 3);
		Stream<Integer> boxedStream = stream.boxed();
//		 boxedStream.forEach(System.out::println);
		long count = boxedStream.peek(System.out::println).count();
		assertEquals(expectedCount, count);
	}
1
2
3

intStreamToList

建立一個 IntStream，增加三個元素，使用 boxed 、 collect 轉成 List ，內有三個元素。

	@Test
	public void intStreamToList() {
		int expectedSize = 3;
		IntStream stream = IntStream.of(1, 2, 3);
		List<Integer> list = stream.boxed().collect(Collectors.toList());
		System.out.println(list);
		assertEquals(expectedSize, list.size());
	}
	
1
2
3

intStreamToArray

建立一個 IntStream，增加三個元素，使用 boxed 、 toArray 轉成 Array ，內有三個元素。

	@Test
	public void intStreamToArray() {
		int expectedSize = 3;
		IntStream stream = IntStream.of(1, 2, 3);
		Integer[] array = stream.boxed().toArray(Integer[]::new);
		System.out.println(Arrays.toString(array));
		assertEquals(expectedSize, array.length);
	}
[1, 2, 3]

longStreamBoxed

Boxed Streams in Java 建立一個 LongStream，增加三個元素，使用 boxed 轉成 Object Stream ，內有三個元素。

	@Test
	public void longStreamBoxed() {
		int expectedCount = 3;
		LongStream stream = LongStream.of(4, 5, 6);
		Stream<Long> boxedStream = stream.boxed();
//		 boxedStream.forEach(System.out::println);
		long count = boxedStream.peek(System.out::println).count();
		assertEquals(expectedCount, count);
	}
4
5
6

longStreamToList

Boxed Streams in Java 建立一個 LongStream，增加三個元素，使用 boxed 、 collect 轉成 List ，內有三個元素。

	@Test
	public void longStreamToList() {
		int expectedSize = 3;
		LongStream stream = LongStream.of(4, 5, 6);
		List<Long> list = stream.boxed().collect(Collectors.toList());
		System.out.println(list);
		assertEquals(expectedSize, list.size());
	}
4
5
6

longStreamToArray

Boxed Streams in Java 建立一個 LongStream，增加三個元素，使用 boxed 、 toArray 轉成 Array ，內有三個元素。

	@Test
	public void longStreamToArray() {
		int expectedSize = 3;
		LongStream stream = LongStream.of(4, 5, 6);
		Long[] array = stream.boxed().toArray(Long[]::new);
		System.out.println(Arrays.toString(array));
		assertEquals(expectedSize, array.length);
	}
[4, 5, 6]

doubleStreamBoxed

Stream Boxed 建立一個 DoubleStream，增加三個元素，使用 boxed 轉成 Object Stream ，內有三個元素。

	@Test
	public void doubleStreamBoxed() {
		int expectedCount = 3;
		DoubleStream stream = DoubleStream.of(7.0, 8.0, 9.0);
		Stream<Double> boxedStream = stream.boxed();
//		 boxedStream.forEach(System.out::println);
		long count = boxedStream.peek(System.out::println).count();
		assertEquals(expectedCount, count);
	}
7.0
8.0
9.0

doubleStreamToList

Stream Boxed 建立一個 DoubleStream，增加三個元素，使用 boxed 、 collect 轉成 List ，內有三個元素。

	@Test
	public void doubleStreamToList() {
		int expectedSize = 3;
		DoubleStream stream = DoubleStream.of(7.0, 8.0, 9.0);
		List<Double> list = stream.boxed().collect(Collectors.toList());
		System.out.println(list);
		assertEquals(expectedSize, list.size());
	}
7.0
8.0
9.0

doubleStreamToArray

Stream Boxed 建立一個 DoubleStream，增加三個元素，使用 boxed 、 toArray 轉成 Array ，內有三個元素。

	@Test
	public void doubleStreamToArray() {
		int expectedSize = 3;
		DoubleStream stream = DoubleStream.of(7.0, 8.0, 9.0);
		Double[] array = stream.boxed().toArray(Double[]::new);
		System.out.println(Arrays.toString(array));
		assertEquals(expectedSize, array.length);
	}
[7.0, 8.0, 9.0]

StreamBoxedTest.java

Primitive Type Streams 新增單元測試，驗證 Boxed Stream 是否符合預期。

package org.ruoxue.java_147.stream;

import static org.junit.Assert.*;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.DoubleStream;
import java.util.stream.IntStream;
import java.util.stream.LongStream;
import java.util.stream.Stream;

import org.junit.Test;

public class StreamBoxedTest {

	public StreamBoxedTest() {

	}

	@Test
	public void intStreamBoxed() {
		int expectedCount = 3;
		IntStream stream = IntStream.of(1, 2, 3);
		Stream<Integer> boxedStream = stream.boxed();
//		 boxedStream.forEach(System.out::println);
		long count = boxedStream.peek(System.out::println).count();
		assertEquals(expectedCount, count);
	}

	@Test
	public void intStreamToList() {
		int expectedSize = 3;
		IntStream stream = IntStream.of(1, 2, 3);
		List<Integer> list = stream.boxed().collect(Collectors.toList());
		System.out.println(list);
		assertEquals(expectedSize, list.size());
	}

	@Test
	public void intStreamToArray() {
		int expectedSize = 3;
		IntStream stream = IntStream.of(1, 2, 3);
		Integer[] array = stream.boxed().toArray(Integer[]::new);
		System.out.println(Arrays.toString(array));
		assertEquals(expectedSize, array.length);
	}

	@Test
	public void longStreamBoxed() {
		int expectedCount = 3;
		LongStream stream = LongStream.of(4, 5, 6);
		Stream<Long> boxedStream = stream.boxed();
//		 boxedStream.forEach(System.out::println);
		long count = boxedStream.peek(System.out::println).count();
		assertEquals(expectedCount, count);
	}

	@Test
	public void longStreamToList() {
		int expectedSize = 3;
		LongStream stream = LongStream.of(4, 5, 6);
		List<Long> list = stream.boxed().collect(Collectors.toList());
		System.out.println(list);
		assertEquals(expectedSize, list.size());
	}

	@Test
	public void longStreamToArray() {
		int expectedSize = 3;
		LongStream stream = LongStream.of(4, 5, 6);
		Long[] array = stream.boxed().toArray(Long[]::new);
		System.out.println(Arrays.toString(array));
		assertEquals(expectedSize, array.length);
	}

	@Test
	public void doubleStreamBoxed() {
		int expectedCount = 3;
		DoubleStream stream = DoubleStream.of(7.0, 8.0, 9.0);
		Stream<Double> boxedStream = stream.boxed();
//		 boxedStream.forEach(System.out::println);
		long count = boxedStream.peek(System.out::println).count();
		assertEquals(expectedCount, count);
	}

	@Test
	public void doubleStreamToList() {
		int expectedSize = 3;
		DoubleStream stream = DoubleStream.of(7.0, 8.0, 9.0);
		List<Double> list = stream.boxed().collect(Collectors.toList());
		System.out.println(list);
		assertEquals(expectedSize, list.size());
	}
	
	@Test
	public void doubleStreamToArray() {
		int expectedSize = 3;
		DoubleStream stream = DoubleStream.of(7.0, 8.0, 9.0);
		Double[] array = stream.boxed().toArray(Double[]::new);
		System.out.println(Arrays.toString(array));
		assertEquals(expectedSize, array.length);
	}

}

心得分享

Boxed Stream  提供了 3 種 基本型別 Stream ，轉成 Object Stream 、 List 、 Array 等。

原碼下載

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