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LinkedBlockingQueue in Java with Examples - Java 147

LinkedBlockingQueue in Java with Examples – Java 147

LinkedBlockingQueue in Java with Examples

是執行緒安全的無界佇列，表示在建立時若未指定佇列的大小，其佇列可以隨著元素的增加而動態增長，但是，如果沒有足夠的記憶體，則會拋出 OutOfMemoryError ，如果有給定大小，那就是固定容量的佇列， Java LinkedBlockingQueue Examples 介紹常見的 forEach 、 iterator 、 spliterator 、 trySplit 、 drainTo 等方法，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
       |               +- queue
       |                   +- linkedblockingqueue
       |                       +- LinkedBlockingQueueMethodsTest.java

單元測試

Java BlockingQueue 提供循環訪問、佇列匯出、轉成陣列等操作列表中的元素。

forEach

建立一個 LinkedBlockingQueue ，內有三個元素，迴圈取得元素。

	@Test
	public void forEach() {
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");
		queue.forEach(e -> System.out.println(e));
	}
Papaya
Strawberry
Watermelon

forEachRemaining

建立一個 LinkedBlockingQueue ，內有三個元素，迴圈取得剩餘元素。

	@Test
	public void forEachRemaining() {
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");
		Iterator<String> it = queue.iterator();
		int i = 0;
		while (it.hasNext()) {
			System.out.println(it.next());
			if (i == 1) {
				break;
			}
			i++;
		}
		System.out.println("----------");
		it.forEachRemaining(e -> {
			System.out.println(e);
		});
	}
Papaya
Strawberry
----------
Watermelon

iterator

Java BlockingQueue 建立一個 LinkedBlockingQueue ，內有三個元素，迴圈取得元素。

	@Test
	public void iterator() {
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");
		Iterator<String> it = queue.iterator();
		while (it.hasNext()) {
			System.out.println(it.next());
		}
	}
Papaya
Strawberry
Watermelon

spliterator

Java BlockingQueue 建立一個 LinkedBlockingQueue ，內有三個元素，使用 spliterator 取得元素，等同於 iterator.hasNext 和 iterator.next。

	@Test
	public void spliterator() {
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");
		Spliterator<String> sit = queue.spliterator();
		sit.tryAdvance(e -> System.out.println(e));
		System.out.println("----------");
		sit.forEachRemaining(e -> System.out.println(e));

		System.out.println("----------");
		sit = queue.spliterator();
		while (sit.tryAdvance(e -> System.out.println(e))) {
		}
	}
Papaya
----------
Strawberry
Watermelon
----------
Papaya
Strawberry
Watermelon

trySplit

Java BlockingQueue 建立一個 LinkedBlockingQueue ，內有三個元素，使用 spliterator 取得元素，trySplit 將目前的拆分器分為兩個新的拆分器並行處理。

	@Test
	public void trySplit() {
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");
		Spliterator<String> sit = queue.spliterator();
		Spliterator<String> sit2 = sit.trySplit();
		System.out.println(sit.getExactSizeIfKnown());
		sit.forEachRemaining(e -> System.out.println(e));

		System.out.println("----------");
		System.out.println(sit2.getExactSizeIfKnown());
		sit2.forEachRemaining(e -> System.out.println(e));
	}
-1
Strawberry
Watermelon
----------
1
Papaya

toArray

Java LinkedBlockingQueue 建立一個 LinkedBlockingQueue ，內有三個元素， 轉換成 String 陣列。

	@Test
	public void toArray() {
		int expectedSize = 3;
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");

		String[] array = new String[queue.size()];
		queue.toArray(array);
		for (String e : array) {
			System.out.println(e);
		}
		assertEquals(expectedSize, array.length);
	}
Papaya
Strawberry
Watermelon

streamToArray

Java LinkedBlockingQueue 建立一個 LinkedBlockingQueue ，內有三個元素，使用 Stream ，轉換成 String 陣列。

	@Test
	public void streamToArray() {
		int expectedSize = 3;
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");

		String[] array = queue.stream().toArray(String[]::new);
		for (String e : array) {
			System.out.println(e);
		}
		assertEquals(expectedSize, array.length);
	}
Papaya
Strawberry
Watermelon

drainTo

建立一個 LinkedBlockingQueue ，內有三個元素，元素全部匯出到另一個佇列。

	@Test
	public void drainTo() {
		int expectedSize = 0;
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");
		System.out.println(queue);
		BlockingQueue<String> queue2 = new LinkedBlockingQueue<String>();
		queue.drainTo(queue2);
		System.out.println(queue);
		System.out.println(queue2);
		assertEquals(expectedSize, queue.size());
		assertEquals(3, queue2.size());
	}
[Papaya, Strawberry, Watermelon]
[]
[Papaya, Strawberry, Watermelon]

drainToMaxElements

建立一個 LinkedBlockingQueue ，內有三個元素，匯出指定數量元素到另一個佇列。

    @Test
	public void drainToMaxElements() {
		int expectedSize = 2;
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");
		System.out.println(queue);
		BlockingQueue<String> queue2 = new LinkedBlockingQueue<String>();
		queue.drainTo(queue2, 1);
		System.out.println(queue);
		System.out.println(queue2);
		assertEquals(expectedSize, queue.size());
		assertEquals(1, queue2.size());
	}
[Papaya, Strawberry, Watermelon]
[Strawberry, Watermelon]
[Papaya]

LinkedBlockingQueueWithExamplesTest.java

Java LinkedBlockingQueue 新增單元測試，驗證是否符合預期。

package org.ruoxue.java_147.queue.linkedblockingqueue;

import static org.junit.Assert.*;

import java.util.Iterator;
import java.util.Spliterator;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;

import org.junit.Test;

public class LinkedBlockingQueueWithExamplesTest {

	@Test
	public void forEach() {
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");
		queue.forEach(e -> System.out.println(e));
	}

	@Test
	public void forEachRemaining() {
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");
		Iterator<String> it = queue.iterator();
		int i = 0;
		while (it.hasNext()) {
			System.out.println(it.next());
			if (i == 1) {
				break;
			}
			i++;
		}
		System.out.println("----------");
		it.forEachRemaining(e -> {
			System.out.println(e);
		});
	}

	@Test
	public void iterator() {
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");
		Iterator<String> it = queue.iterator();
		while (it.hasNext()) {
			System.out.println(it.next());
		}
	}

	@Test
	public void spliterator() {
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");
		Spliterator<String> sit = queue.spliterator();
		sit.tryAdvance(e -> System.out.println(e));
		System.out.println("----------");
		sit.forEachRemaining(e -> System.out.println(e));

		System.out.println("----------");
		sit = queue.spliterator();
		while (sit.tryAdvance(e -> System.out.println(e))) {
		}
	}

	@Test
	public void trySplit() {
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");
		Spliterator<String> sit = queue.spliterator();
		Spliterator<String> sit2 = sit.trySplit();
		System.out.println(sit.getExactSizeIfKnown());
		sit.forEachRemaining(e -> System.out.println(e));

		System.out.println("----------");
		System.out.println(sit2.getExactSizeIfKnown());
		sit2.forEachRemaining(e -> System.out.println(e));
	}

	@Test
	public void toArray() {
		int expectedSize = 3;
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");

		String[] array = new String[queue.size()];
		queue.toArray(array);
		for (String e : array) {
			System.out.println(e);
		}
		assertEquals(expectedSize, array.length);
	}

	@Test
	public void streamToArray() {
		int expectedSize = 3;
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");

		String[] array = queue.stream().toArray(String[]::new);
		for (String e : array) {
			System.out.println(e);
		}
		assertEquals(expectedSize, array.length);
	}

	@Test
	public void drainTo() {
		int expectedSize = 0;
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");
		System.out.println(queue);
		BlockingQueue<String> queue2 = new LinkedBlockingQueue<String>();
		queue.drainTo(queue2);
		System.out.println(queue);
		System.out.println(queue2);
		assertEquals(expectedSize, queue.size());
		assertEquals(3, queue2.size());
	}

	@Test
	public void drainToMaxElements() {
		int expectedSize = 2;
		BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
		queue.add("Papaya");
		queue.add("Strawberry");
		queue.add("Watermelon");
		System.out.println(queue);
		BlockingQueue<String> queue2 = new LinkedBlockingQueue<String>();
		queue.drainTo(queue2, 1);
		System.out.println(queue);
		System.out.println(queue2);
		assertEquals(expectedSize, queue.size());
		assertEquals(1, queue2.size());
	}
}

心得分享

Java BlockingQueue Examples 執行緒安全是通過悲觀鎖來保證的，使用兩個獨立的 ReentrantLocks 進行寫和讀操作，這可以防止生產者和消費者執行緒之間的訪問衝突， ArrayBlockingQueue 僅受一個 ReentrantLock 保護，因此生產者線程和消費者執行緒之間的訪問衝突是有可能的， Java LinkedBlockingQueue 提供了幾種 LinkedBlockingQueue 常見方法的操作範例。

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