Java LinkedHashSet Class - Java 147

Java LinkedHashSet Class – Java 147

Java LinkedHashSet Class

繼承 HashSet 實作集合框架的 Set 接口,集合中的元素,不可重複,會依新增順序保持排序, LinkedHashSet Class 介紹常見的 contains 、 stream 、 retainAll 等方法,了解 Set 的不同操作和方法,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
       |                   +- linkedhashset
       |                       +- LinkedHashSetClassTest.java 

單元測試

LinkedHashSet Class Java 提供檢查包含、串流操作列表中的元素。

contains

LinkedHashSet Class Java 建立 Fruit 物件,覆寫 equals 、 hashCode 提供給集合比較使用,建立一個 LinkedHashSet ,增加三個元素,檢查包含指定的元素。

	@NoArgsConstructor
	@Getter
	@Setter
	@Builder
	public static class Fruit {
		private String name;
		private double quantity;
		private int type;

		public Fruit(String name, double quantity, int type) {
			this.name = name;
			this.quantity = quantity;
			this.type = type;
		}

		public String toString() {
			ToStringBuilder builder = new ToStringBuilder(this, ToStringStyle.JSON_STYLE);
			builder.appendSuper(super.toString());
			builder.append("name", name);
			builder.append("quantity", quantity);
			builder.append("type", type);
			return builder.toString();
		}

		public boolean equals(Object object) {
			if (!(object instanceof Fruit)) {
				return false;
			}
			if (this == object) {
				return true;
			}
			Fruit other = (Fruit) object;
			return new EqualsBuilder().append(getName(), other.getName()).isEquals();
		}

		public int hashCode() {
			return new HashCodeBuilder().append(getName()).toHashCode();
		}
	}

	@Test
	public void contains() {
		Set<Fruit> set = new LinkedHashSet<>();
		set.add(new Fruit("Longan", 1, 1));
		set.add(new Fruit("Tomato", 2, 1));
		set.add(new Fruit("Pear", 3, 1));

		boolean contains = set.contains(new Fruit("Longan", 1, 1));
		System.out.println(contains);
		assertTrue(contains);

		contains = set.contains(new Fruit("Grape", 4, 1));
		System.out.println(contains);
		assertFalse(contains);
	}
true
false

containsAll

LinkedHashSet Class Java 建立一個 LinkedHashSet ,內有三個元素,檢查包含所有指定的元素。

	@Test
	public void containsAll() {
		Set<Fruit> set = new LinkedHashSet<>();
		set.add(new Fruit("Longan", 1, 1));
		set.add(new Fruit("Tomato", 2, 1));
		set.add(new Fruit("Pear", 3, 1));

		Set<Fruit> set2 = new LinkedHashSet<>();
		set.add(new Fruit("Longan", 1, 1));
		set.add(new Fruit("Tomato", 2, 1));

		boolean contains = set.containsAll(set2);
		System.out.println(contains);
		assertTrue(contains);

		contains = set2.containsAll(set);
		System.out.println(contains);
		assertFalse(contains);
	}
true
false

stream

LinkedHashSet Class Java 建立一個 LinkedHashSet ,內有三個元素,執行串流,取得長度小於 6 的元素。

	@Test
	public void stream() {
		int expectedSize = 1;
		Set<Fruit> set = new LinkedHashSet<>();
		set.add(new Fruit("Longan", 1, 1));
		set.add(new Fruit("Tomato", 2, 1));
		set.add(new Fruit("Pear", 3, 1));
		set = set.stream().filter(e -> e.getName().length() < 6).collect(Collectors.toSet());
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}
[{"name":"Pear","quantity":3.0,"type":1}]

parallelStream

LinkedHashSet Class Java 建立一個 LinkedHashSet ,內有三個元素,並行執行串流。

	@Test
	public void parallelStream() {
		Set<Fruit> set = new LinkedHashSet<>();
		set.add(new Fruit("Longan", 1, 1));
		set.add(new Fruit("Tomato", 2, 1));
		set.add(new Fruit("Pear", 3, 1));
		set.parallelStream().forEach(System.out::println);
		System.out.println("----------");
		set.parallelStream().forEachOrdered(System.out::println);
	}
{"name":"Tomato","quantity":2.0,"type":1}
{"name":"Longan","quantity":1.0,"type":1}
{"name":"Pear","quantity":3.0,"type":1}
----------
{"name":"Longan","quantity":1.0,"type":1}
{"name":"Tomato","quantity":2.0,"type":1}
{"name":"Pear","quantity":3.0,"type":1}

retainAll

Linked Hash Set Class in Java 建立兩個 LinkedHashSet ,內各有三個元素,只保留相同元素 。

	@Test
	public void retainAll() {
		Set<Fruit> set = new LinkedHashSet<>();
		set.add(new Fruit("Longan", 1, 1));
		set.add(new Fruit("Tomato", 2, 1));
		set.add(new Fruit("Pear", 3, 1));

		Set<Fruit> set2 = new LinkedHashSet<>();
		set2.add(new Fruit("Longan", 1, 1));
		set2.add(new Fruit("Lemon", 4, 1));
		set2.add(new Fruit("Mango", 5, 1));

		boolean result = set.retainAll(set2);
		System.out.println(result);
		System.out.println(set);
		assertTrue(result);

		result = set.retainAll(set2);
		System.out.println(result);
		System.out.println(set);
		assertFalse(result);
	}
true
[{"name":"Longan","quantity":1.0,"type":1}]
false
[{"name":"Longan","quantity":1.0,"type":1}]

LinkedHashSetClassTest.java

Linked Hash Set Class in Java 新增單元測試,驗證是否符合預期。

package org.ruoxue.java_147.set.linkedhashset;

import static org.junit.Assert.*;

import java.util.LinkedHashSet;
import java.util.Set;
import java.util.stream.Collectors;

import org.apache.commons.lang3.builder.EqualsBuilder;
import org.apache.commons.lang3.builder.HashCodeBuilder;
import org.apache.commons.lang3.builder.ToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;
import org.junit.Test;

import lombok.Builder;
import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;

public class LinkedHashSetClassTest {

	@NoArgsConstructor
	@Getter
	@Setter
	@Builder
	public static class Fruit {
		private String name;
		private double quantity;
		private int type;

		public Fruit(String name, double quantity, int type) {
			this.name = name;
			this.quantity = quantity;
			this.type = type;
		}

		public String toString() {
			ToStringBuilder builder = new ToStringBuilder(this, ToStringStyle.JSON_STYLE);
			builder.appendSuper(super.toString());
			builder.append("name", name);
			builder.append("quantity", quantity);
			builder.append("type", type);
			return builder.toString();
		}

		public boolean equals(Object object) {
			if (!(object instanceof Fruit)) {
				return false;
			}
			if (this == object) {
				return true;
			}
			Fruit other = (Fruit) object;
			return new EqualsBuilder().append(getName(), other.getName()).isEquals();
		}

		public int hashCode() {
			return new HashCodeBuilder().append(getName()).toHashCode();
		}
	}

	@Test
	public void contains() {
		Set<Fruit> set = new LinkedHashSet<>();
		Fruit fruit = new Fruit("Longan", 1, 1);
		set.add(fruit);
		set.add(new Fruit("Tomato", 2, 1));
		set.add(new Fruit("Pear", 3, 1));

		boolean contains = set.contains(fruit);
		System.out.println(contains);
		assertTrue(contains);

		contains = set.contains(new Fruit("Grape", 4, 1));
		System.out.println(contains);
		assertFalse(contains);
	}

	@Test
	public void containsAll() {
		Set<Fruit> set = new LinkedHashSet<>();
		set.add(new Fruit("Longan", 1, 1));
		set.add(new Fruit("Tomato", 2, 1));
		set.add(new Fruit("Pear", 3, 1));

		Set<Fruit> set2 = new LinkedHashSet<>();
		set.add(new Fruit("Longan", 1, 1));
		set.add(new Fruit("Tomato", 2, 1));

		boolean contains = set.containsAll(set2);
		System.out.println(contains);
		assertTrue(contains);

		contains = set2.containsAll(set);
		System.out.println(contains);
		assertFalse(contains);
	}

	@Test
	public void stream() {
		int expectedSize = 1;
		Set<Fruit> set = new LinkedHashSet<>();
		set.add(new Fruit("Longan", 1, 1));
		set.add(new Fruit("Tomato", 2, 1));
		set.add(new Fruit("Pear", 3, 1));
		set = set.stream().filter(e -> e.getName().length() < 6).collect(Collectors.toSet());
		System.out.println(set);
		assertEquals(expectedSize, set.size());
	}

	@Test
	public void parallelStream() {
		Set<Fruit> set = new LinkedHashSet<>();
		set.add(new Fruit("Longan", 1, 1));
		set.add(new Fruit("Tomato", 2, 1));
		set.add(new Fruit("Pear", 3, 1));
		set.parallelStream().forEach(System.out::println);
		System.out.println("----------");
		set.parallelStream().forEachOrdered(System.out::println);
	}

	@Test
	public void retainAll() {
		Set<Fruit> set = new LinkedHashSet<>();
		set.add(new Fruit("Longan", 1, 1));
		set.add(new Fruit("Tomato", 2, 1));
		set.add(new Fruit("Pear", 3, 1));

		Set<Fruit> set2 = new LinkedHashSet<>();
		set2.add(new Fruit("Longan", 1, 1));
		set2.add(new Fruit("Lemon", 4, 1));
		set2.add(new Fruit("Mango", 5, 1));

		boolean result = set.retainAll(set2);
		System.out.println(result);
		System.out.println(set);
		assertTrue(result);

		result = set.retainAll(set2);
		System.out.println(result);
		System.out.println(set);
		assertFalse(result);
	}
}

心得分享

Java LinkedHashSet Class Example 保持新增順序會產生額外的相關成本,包括花費額外的 CPU 和需要更多的記憶體,如果不需要維護新增順序,建議改用輕量級的 HashSet , Linked Hash Set Class in Java 在應用上相當廣泛,熟悉這些方法的操作,如: contains 、 stream 、 retainAll 等,提供了幾種 LinkedHashSet 常見範例。

發佈留言