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ConcurrentHashSet in Java with Examples - Java 147

ConcurrentHashSet in Java with Examples – Java 147

ConcurrentHashSet in Java with Examples

調用 keySet (defaultValue) 和 newKeySet 的方法傳回 Set，可以新增元素以及執行其他集合運算， ConcurrentHashSet in Java 介紹常見的 forEach 、 iterator 、 spliterator 、 trySplit 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
       |               +- set
       |                   +- concurrenthashset
       |                       +- ConcurrentHashSetWithExamplesTest.java

單元測試

ConcurrentHashSet Java 提供循環訪問、轉成陣列等操作 Set 中的元素。

forEach

使用 ConcurrentHashMap newKeySet ，取得 Set ，增加三個元素，迴圈取得元素。

	@Test
	public void forEach() {
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		set.forEach(e -> System.out.println(e));
	}
Pear
Longan
Tomato

forEachRemaining

ConcurrentHashSet Java 使用 ConcurrentHashMap newKeySet ，取得 Set ，增加三個元素，迴圈取得剩餘元素。

	@Test
	public void forEachRemaining() {
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		Iterator<String> it = set.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);
		});
	}
Pear
Longan
----------
Tomato

iterator

ConcurrentHashSet Java 使用 ConcurrentHashMap newKeySet ，取得 Set ，增加三個元素，迴圈取得元素。

	@Test
	public void iterator() {
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		Iterator<String> it = set.iterator();
		while (it.hasNext()) {
			System.out.println(it.next());
		}
	}
Pear
Longan
Tomato

spliterator

ConcurrentHashSet Java 使用 ConcurrentHashMap newKeySet ，取得 Set ，增加三個元素，使用 spliterator 取得元素，等同於 iterator.hasNext 和 iterator.next。

	@Test
	public void spliterator() {
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		Spliterator<String> sit = set.spliterator();
		sit.tryAdvance(e -> System.out.println(e));
		System.out.println("----------");
		sit.forEachRemaining(e -> System.out.println(e));

		System.out.println("----------");
		sit = set.spliterator();
		while (sit.tryAdvance(e -> System.out.println(e))) {
		}
	}
Pear
----------
Longan
Tomato
----------
Pear
Longan
Tomato

trySplit

Java ConcurrentHashSet 使用 ConcurrentHashMap newKeySet ，取得 Set ，增加三個元素，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() {
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		Spliterator<String> sit = set.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
Longan
Tomato
----------
-1
Pear

toArray

Java ConcurrentHashSet 使用 ConcurrentHashMap newKeySet ，取得 Set ，增加三個元素，轉換成 String 陣列。

	@Test
	public void toArray() {
		int expectedSize = 3;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");

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

streamToArray

Java ConcurrentHashSet 使用 ConcurrentHashMap newKeySet ，取得 Set ，增加三個元素，使用 Stream ，轉換成 String 陣列。

	@Test
	public void streamToArray() {
		int expectedSize = 3;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");

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

ConcurrentHashSetWithExamplesTest.java

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

package org.ruoxue.java_147.set.concurrenthashset;

import static org.junit.Assert.*;

import java.util.Iterator;
import java.util.Set;
import java.util.Spliterator;
import java.util.concurrent.ConcurrentHashMap;

import org.junit.Test;

public class ConcurrentHashSetWithExamplesTest {

	@Test
	public void forEach() {
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		set.forEach(e -> System.out.println(e));
	}

	@Test
	public void forEachRemaining() {
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		Iterator<String> it = set.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() {
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		Iterator<String> it = set.iterator();
		while (it.hasNext()) {
			System.out.println(it.next());
		}
	}

	@Test
	public void spliterator() {
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		Spliterator<String> sit = set.spliterator();
		sit.tryAdvance(e -> System.out.println(e));
		System.out.println("----------");
		sit.forEachRemaining(e -> System.out.println(e));

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

	@Test
	public void trySplit() {
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		Spliterator<String> sit = set.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;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");

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

	@Test
	public void streamToArray() {
		int expectedSize = 3;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");

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

心得分享

Java ConcurrentHashSet Example 從 JDK 8 開始，可以使用新加入的 keySet (defaultValue) 和 newKeySet 方法，建立一個由 ConcurrentHashMap 支援的 ConcurrentHashSet ，提供了幾種常見方法的操作範例，在應用上相當廣泛，熟悉 Java ConcurrentHashSet 這些方法的操作，可以快速撰寫程式，降低錯誤率，再輔以單元測試驗證，建置高效穩定的服務或系統。

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