ArrayList 與 List 關系與代碼示例 - Java

關系

List 是 Java Interface, ArrayList 是 Java Class，它們都屬於 java.util 包。

Java List 是有序的集合（ordered collection），也稱為序列（Sequence）；

Java ArrayList 是 Java List Interface 的可變大小的數組實現。

這兩者在 JAVA collection framework 位置，如下圖所示：

再來看看官方文檔說明：

java.util

Interface List<E>

• Type Parameters:

E - the type of elements in this list

All Superinterfaces:

Collection<E>, Iterable<E>

All Known Implementing Classes:

AbstractList, AbstractSequentialList, ArrayList, AttributeList, CopyOnWriteArrayList, LinkedList, RoleList, RoleUnresolvedList, Stack, Vector

---

public interface List<E>

extends Collection<E>

An ordered collection (also known as a sequence).

 

java.util

Class ArrayList<E>

• java.lang.Object
  • java.util.AbstractCollection<E>
    • java.util.AbstractList<E>
      • java.util.ArrayList<E>

All Implemented Interfaces:

Serializable, Cloneable, Iterable<E>, Collection<E>, List<E>, RandomAccess

Direct Known Subclasses:

AttributeList, RoleList, RoleUnresolvedList

---

public class ArrayList<E>

extends AbstractList<E>

implements List<E>, RandomAccess, Cloneable, Serializable

Resizable-array implementation of the List interface.

 

示例

1. 新建一個 ArrayList 對象

List<String> brands = new ArrayList<String>();

2. 向其中增加元素

brands.add("Jack Amber");

3. 完整示例

// BeerExpert.java, excerpted from Dawn Griffiths & David Griffiths, "Head First Android Development", 2015
import java.util.ArrayList; import java.util.List; public class BeerExpert { List<String> getBrands (String color) { List<String> brands = new ArrayList<String>(); if (color.equals("amber")) { brands.add("Jack Amber"); brands.add("Red Moose"); } else { brands.add("Jail Pale Ale"); brands.add("Gout Stout"); } return brands; } }

 

參考資料

[1] Oracle Corporation. Class ArrayList<E> - Java™ Platform Standard Ed. 8 [OL]. https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html

[2] Oracle Corporation. Interface List<E> - Java™ Platform Standard Ed. 8 [OL]. https://docs.oracle.com/javase/8/docs/api/java/util/List.html

[3] Stack Overflow Users. Type List vs type ArrayList in Java [OL]. https://stackoverflow.com/questions/2279030/type-list-vs-type-arraylist-in-java