Table of Contents
ToggleJava 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。