Table of Contents
ToggleJava LinkedHashMap Methods
允許儲存空鍵、空值,但只能有一個 Null Key ,保證新增時的順序,介紹常見的 put 、 get 、 clear 、 size 等方法,將資料存儲在鍵、值對中,可以通過另一種類型的索引訪問,當插入重複鍵時,會替換相應鍵的元素, LinkedHashMap Java Methods 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
| +- map
| +- linkedhashmap
| +- LinkedHashMapMethodsTest.java
單元測試
LinkedHashMap Methods Java 提供新增、取得、修改、刪除等操作 Map 中的元素。
Fruit
LinkedHashMap Methods Java 建立 Fruit 物件,覆寫 equals 、 hashCode ,定義屬性和方法,用來建立一個物件。
@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();
}
}
put
LinkedHashMap Methods Java 建立一個 LinkedHashMap ,增加三個元素。
@Test
public void put() {
int expectedSize = 3;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
System.out.println(map);
assertEquals(expectedSize, map.size());
}
{Grape={"name":"Grape","quantity":1.0,"type":1}, Kiwifruit={"name":"Kiwifruit","quantity":2.0,"type":1}, Lemon={"name":"Lemon","quantity":3.0,"type":1}}
putIfAbsent
LinkedHashMap Methods Java 建立一個 LinkedHashMap ,當元素不存在時,新增元素。
@Test
public void putIfAbsent() {
int expectedSize = 3;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
Fruit put = map.putIfAbsent("Lemon", new Fruit("Lemon", 3, 1));
System.out.println(put);
assertNull(put);
System.out.println(map);
assertEquals(expectedSize, map.size());
}
null
{Grape={"name":"Grape","quantity":1.0,"type":1}, Kiwifruit={"name":"Kiwifruit","quantity":2.0,"type":1}, Lemon={"name":"Lemon","quantity":3.0,"type":1}}
get
LinkedHashMap Methods in Java 建立一個 LinkedHashMap ,內有三個元素,取得指定 Key 元素。
@Test
public void get() {
double expected = 2d;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
Fruit value = map.get("Kiwifruit");
System.out.println(value);
assertEquals(expected, value.getQuantity(), 0);
}
{"name":"Kiwifruit","quantity":2.0,"type":1}
getOrDefault
LinkedHashMap Methods in Java 建立一個 LinkedHashMap ,內有三個元素,取得指定 Key 元素,若不存在傳回預設值。
@Test
public void getOrDefault() {
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
Fruit result = map.getOrDefault("", new Fruit("Empty", 0, 0));
System.out.println(result);
assertNotNull(result);
}
{"name":"Empty","quantity":0.0,"type":0}
update
LinkedHashMap Methods in Java 建立一個 LinkedHashMap ,內有三個元素,更新指定 Key 元素。
@Test
public void update() {
double expected = 10d;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
System.out.println(map);
Fruit put = map.put("Grape", new Fruit("Grape", 10, 1));
assertEquals(1d, put.getQuantity(), 0);
System.out.println(map);
assertEquals(expected, map.get("Grape").getQuantity(), 0);
}
{Grape={"name":"Grape","quantity":1.0,"type":1}, Kiwifruit={"name":"Kiwifruit","quantity":2.0,"type":1}, Lemon={"name":"Lemon","quantity":3.0,"type":1}}
{Grape={"name":"Grape","quantity":10.0,"type":1}, Kiwifruit={"name":"Kiwifruit","quantity":2.0,"type":1}, Lemon={"name":"Lemon","quantity":3.0,"type":1}}
remove
LinkedHashMap Methods in Java 建立一個 LinkedHashMap ,內有三個元素,刪除指定 Key 元素。
@Test
public void remove() {
int expectedSize = 2;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
map.remove("Grape");
System.out.println(map);
assertEquals(expectedSize, map.size());
}
{Kiwifruit={"name":"Kiwifruit","quantity":2.0,"type":1}, Lemon={"name":"Lemon","quantity":3.0,"type":1}}
clear
LinkedHashMap Functions in Java 建立一個 LinkedHashMap ,內有三個元素,刪除所有元素。
@Test
public void clear() {
int expectedSize = 0;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
map.clear();
System.out.println(map);
assertEquals(expectedSize, map.size());
}
{}
size
LinkedHashMap Functions in Java 建立一個 LinkedHashMap ,內有三個元素,取得長度。
@Test
public void size() {
int expectedSize = 3;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
System.out.println(map.size());
assertEquals(expectedSize, map.size());
}
3
putAll
LinkedHashMap Functions in Java 建立兩個 LinkedHashMap ,內各有三個元素,合併成為一個 Map 。
@Test
public void putAll() {
int expectedSize = 6;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
Map<String, Fruit> newMap = new LinkedHashMap<>();
newMap.put("Apple", new Fruit("Apple", 4, 1));
newMap.put("Banana", new Fruit("Banana", 5, 1));
newMap.put("Cherry", new Fruit("Cherry", 6, 1));
map.putAll(newMap);
System.out.println(map);
assertEquals(expectedSize, map.size());
}
{Grape={"name":"Grape","quantity":1.0,"type":1}, Kiwifruit={"name":"Kiwifruit","quantity":2.0,"type":1}, Lemon={"name":"Lemon","quantity":3.0,"type":1}, Apple={"name":"Apple","quantity":4.0,"type":1}, Banana={"name":"Banana","quantity":5.0,"type":1}, Cherry={"name":"Cherry","quantity":6.0,"type":1}}
isEmpty
建立一個 LinkedHashMap ,檢查是否為空 Map 。
@Test
public void isEmpty() {
Map<String, Fruit> map = new LinkedHashMap<>();
System.out.println(map.isEmpty());
assertTrue(map.isEmpty());
map.put("Grape", new Fruit("Grape", 1, 1));
System.out.println(map.isEmpty());
assertFalse(map.isEmpty());
}
true
false
LinkedHashMapMethodsTest.java
LinkedHashMap Methods in Java 新增單元測試,驗證是否符合預期。
package org.ruoxue.java_147.map.linkedhashmap;
import static org.junit.Assert.*;
import java.util.LinkedHashMap;
import java.util.Map;
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 LinkedHashMapMethodsTest {
@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 put() {
int expectedSize = 3;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
System.out.println(map);
assertEquals(expectedSize, map.size());
}
@Test
public void putIfAbsent() {
int expectedSize = 3;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
Fruit put = map.putIfAbsent("Lemon", new Fruit("Lemon", 3, 1));
System.out.println(put);
assertNull(put);
System.out.println(map);
assertEquals(expectedSize, map.size());
}
@Test
public void get() {
double expected = 2d;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
Fruit value = map.get("Kiwifruit");
System.out.println(value);
assertEquals(expected, value.getQuantity(), 0);
}
@Test
public void getOrDefault() {
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
Fruit result = map.getOrDefault("", new Fruit("Empty", 0, 0));
System.out.println(result);
assertNotNull(result);
}
@Test
public void update() {
double expected = 10d;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
System.out.println(map);
Fruit put = map.put("Grape", new Fruit("Grape", 10, 1));
assertEquals(1d, put.getQuantity(), 0);
System.out.println(map);
assertEquals(expected, map.get("Grape").getQuantity(), 0);
}
@Test
public void remove() {
int expectedSize = 2;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
map.remove("Grape");
System.out.println(map);
assertEquals(expectedSize, map.size());
}
@Test
public void clear() {
int expectedSize = 0;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
map.clear();
System.out.println(map);
assertEquals(expectedSize, map.size());
}
@Test
public void size() {
int expectedSize = 3;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
System.out.println(map.size());
assertEquals(expectedSize, map.size());
}
@Test
public void putAll() {
int expectedSize = 6;
Map<String, Fruit> map = new LinkedHashMap<>();
map.put("Grape", new Fruit("Grape", 1, 1));
map.put("Kiwifruit", new Fruit("Kiwifruit", 2, 1));
map.put("Lemon", new Fruit("Lemon", 3, 1));
Map<String, Fruit> map2 = new LinkedHashMap<>();
map2.put("Apple", new Fruit("Apple", 4, 1));
map2.put("Banana", new Fruit("Banana", 5, 1));
map2.put("Cherry", new Fruit("Cherry", 6, 1));
map.putAll(map2);
System.out.println(map);
assertEquals(expectedSize, map.size());
}
@Test
public void isEmpty() {
Map<String, Fruit> map = new LinkedHashMap<>();
System.out.println(map.isEmpty());
assertTrue(map.isEmpty());
map.put("Grape", new Fruit("Grape", 1, 1));
System.out.println(map.isEmpty());
assertFalse(map.isEmpty());
}
}
心得分享
LinkedHashMap Functions in Java 實作集合框架的 Map 接口,繼承 HashMap,使用雙向鏈結的方式實作,保證新增時的順序,熟悉 LinkedHashMap Methods in Java 這些方法的操作,提升開發效率,在應用上相當廣泛。