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Java ConcurrentHashSet Methods - Java 147

Java ConcurrentHashSet Methods – Java 147

Java ConcurrentHashSet Methods

在 java.util.concurrent 套件並沒有 ConcurrentHashSet 的類別，但從 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 ， ConcurrentHashSet Java Methods 介紹常見的 add 、 remove 、 clear 、 size 等方法，了解 Set 的不同操作和方法，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
       |                       +- ConcurrentHashSetMethodsTest.java

單元測試

ConcurrentHashSet Methods Java 提供新增、刪除等操作 Set 中的元素。

newKeySet

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

	@Test
	public void newKeySet() {
		int expectedSize = 3;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}
[Pear, Longan, Tomato]

keySet

ConcurrentHashSet Methods Java 建立一個 ConcurrentHashMap ，使用 keySet ，取得 Set ，增加三個元素。

	@Test
	public void keySet() {
		int expectedSize = 3;
		ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
		map.put("Longan", 1);
		map.put("Tomato", 2);
		map.put("Pear", 3);
		System.out.println(map);
		Set<String> set = map.keySet();
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}
{Pear=3, Longan=1, Tomato=2}
[Pear, Longan, Tomato]

keySetDefaultValue

ConcurrentHashSet Methods Java 建立一個 ConcurrentHashMap ，使用 keySet ，設定預設值，取得 Set ，增加三個元素。

	@Test
	public void keySetDefaultValue() {
		int expectedSize = 3;
		ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
		Set<String> set = map.keySet(0);
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		System.out.println(map);
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}
{Pear=0, Longan=0, Tomato=0}
[Pear, Longan, Tomato]

Sets_newConcurrentHashSet

ConcurrentHashSet Methods Java 建立一個 ConcurrentHashMap ，使用 Guava Sets newConcurrentHashSet ，取得 Set ，增加三個元素。

	@Test
	public void Sets_newConcurrentHashSet() {
		int expectedSize = 3;
		Set<String> set = Sets.newConcurrentHashSet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}
[Pear, Longan, Tomato]

addAll

ConcurrentHashSet Methods in Java 建立兩個 ConcurrentHashMap ，使用 newKeySet，取得 Set ，各有三個元素，合併成為一個 Set 。

	@Test
	public void addAll() {
		int expectedSize = 6;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");

		Set<String> set2 = ConcurrentHashMap.newKeySet();
		set2.add("Grape");
		set2.add("Lemon");
		set2.add("Mango");

		set.addAll(set2);
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}
[Pear, Grape, Mango, Longan, Tomato, Lemon]

remove

ConcurrentHashSet Methods in Java 建立一個 ConcurrentHashMap ，使用 newKeySet ，取得 Set ，內有三個元素，刪除指定元素。

	@Test
	public void remove() {
		int expectedSize = 2;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		set.remove("Longan");
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}
[Pear, Tomato]

removeAll

ConcurrentHashSet Methods in Java 建立一個 ConcurrentHashMap ，使用 newKeySet ，取得 Set ，內有三個元素，刪除來自另一個 Set 中的元素。

	@Test
	public void removeAll() {
		int expectedSize = 1;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");

		Set<String> set2 = ConcurrentHashMap.newKeySet();
		set2.add("Longan");
		set2.add("Tomato");
		set2.add("Mango");
		set.removeAll(set2);
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}
[Pear]

clear

ConcurrentHashSet Methods in Java 建立一個 ConcurrentHashMap ，使用 newKeySet ，取得 Set ，內有三個元素，刪除所有元素。

	@Test
	public void clear() {
		int expectedSize = 0;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		set.clear();
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}
[]

size

ConcurrentHashSet Methods in Java 建立一個 ConcurrentHashMap ，使用 newKeySet ，取得 Set ，內有三個元素，取得集合大小。

	@Test
	public void size() {
		int expectedSize = 3;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		System.out.println(set.size());
		assertEquals(expectedSize, set.size());
	}
3

isEmpty

ConcurrentHashSet Methods in Java 建立一個 ConcurrentHashMap ，使用 newKeySet ，取得 Set ，檢查是否為空 Set 。

	@Test
	public void isEmpty() {
		Set<String> set = ConcurrentHashMap.newKeySet();
		System.out.println(set.isEmpty());
		assertTrue(set.isEmpty());
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		System.out.println(set.isEmpty());
		assertFalse(set.isEmpty());
	}
true
false

ConcurrentHashSetMethodsTest.java

ConcurrentHashSet Methods in Java 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.Set;
import java.util.concurrent.ConcurrentHashMap;

import org.junit.Test;

import com.google.common.collect.Sets;

public class ConcurrentHashSetMethodsTest {

	@Test
	public void newKeySet() {
		int expectedSize = 3;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}

	@Test
	public void keySet() {
		int expectedSize = 3;
		ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
		map.put("Longan", 1);
		map.put("Tomato", 2);
		map.put("Pear", 3);
		System.out.println(map);
		Set<String> set = map.keySet();
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}

	@Test
	public void keySetDefaultValue() {
		int expectedSize = 3;
		ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
		Set<String> set = map.keySet(0);
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		System.out.println(map);
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}

	@Test
	public void Sets_newConcurrentHashSet() {
		int expectedSize = 3;
		Set<String> set = Sets.newConcurrentHashSet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}

	@Test
	public void addAll() {
		int expectedSize = 6;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");

		Set<String> set2 = ConcurrentHashMap.newKeySet();
		set2.add("Grape");
		set2.add("Lemon");
		set2.add("Mango");

		set.addAll(set2);
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}

	@Test
	public void remove() {
		int expectedSize = 2;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		set.remove("Longan");
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}

	@Test
	public void removeAll() {
		int expectedSize = 1;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");

		Set<String> set2 = ConcurrentHashMap.newKeySet();
		set2.add("Longan");
		set2.add("Tomato");
		set2.add("Mango");
		set.removeAll(set2);
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}

	@Test
	public void clear() {
		int expectedSize = 0;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		set.clear();
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}

	@Test
	public void size() {
		int expectedSize = 3;
		Set<String> set = ConcurrentHashMap.newKeySet();
		set.add("Longan");
		set.add("Tomato");
		set.add("Pear");
		System.out.println(set.size());
		assertEquals(expectedSize, set.size());
	}

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

心得分享

ConcurrentHashSet Functions in Java 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，例如 add 、 remove 、 clear 、 size 等，熟悉 ConcurrentHashSet Methods in Java 這些方法的操作，可以快速撰寫程式，降低錯誤率。

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