Java ArrayList

先来一段代码：

import java.util.ArrayList;
import java.util.Iterator;

public class ArrayListExample {

    public static void main(String args[]) {
        ArrayList<String> list = new ArrayList<String>();

        list.add("Item1");
        list.add("Item2");
        list.add(2, "Item3");
        list.add("Item4");

        System.out.println("The arraylist contains the following elements: " + list);

        int pos = list.indexOf("Item2");
        System.out.println("The index of Item2 is: " + pos);

        boolean check = list.isEmpty();
        System.out.println("Checking if the arraylist is empty: " + check);

        int size = list.size();
        System.out.println("The size of the list is: " + size);

        boolean element = list.contains("Item5");
        System.out.println("Checking if the arraylist contains the object Item5: " + element);

        String item = list.get(0);
        System.out.println("The item is the index 0 is: " + item);

        System.out.println("Retrieving items with loop using index and size list");
        for (int i = 0; i < list.size(); i++) {
            System.out.println("Index: " + i + " - Item: " + list.get(i));
        }

        System.out.println("Retrieving items using foreach loop");
        for (String str : list) {
            System.out.println("Item is: " + str);
        }

        System.out.println("Retrieving items using iterator");
        for (Iterator<String> it = list.iterator(); it.hasNext();) {
            System.out.println("Item is: " + it.next());
        }

        list.set(1, "NewItem");
        System.out.println("The arraylist after the replacement is: " + list);

        list.remove(0);

        list.remove("Item3");

        System.out.println("The final contents of the arraylist are: " + list);

        String[] simpleArray = list.toArray(new String[list.size()]);
        System.out.println("The array created after the conversion of our arraylist is: " + Arrays.toString(simpleArray));
    }
}

运行结果：

The arraylist contains the following elements: [Item1, Item2, Item3, Item4]
The index of Item2 is: 1
Checking if the arraylist is empty: false
The size of the list is: 4
Checking if the arraylist contains the object Item5: false
The item is the index 0 is: Item1
Retrieving items with loop using index and size list
Index: 0 - Item: Item1
Index: 1 - Item: Item2
Index: 2 - Item: Item3
Index: 3 - Item: Item4
Retrieving items using foreach loop
Item is: Item1
Item is: Item2
Item is: Item3
Item is: Item4
Retrieving items using iterator
Item is: Item1
Item is: Item2
Item is: Item3
Item is: Item4
The arraylist after the replacement is: [Item1, NewItem, Item3, Item4]
The final contents of the arraylist are: [NewItem, Item4]
The array created after the conversion of our arraylist is: [NewItem, Item4]

逐一分析

创建一个 ArrayList 空对象，泛型指定列表元素类型为 String

ArrayList<String> list = new ArrayList<String>();

给 ArrayList 空对象添加数据

添加格式：

boolean add(E element);        // 在列表最后添加元素
void add(int index, E element);        // 在指定位置添加元素，从 0 开始

代码示例：

list.add("Item1");
list.add("Item2");
list.add(2, "Item3");
list.add("Item4");

获取某元素所在的位置

格式：

int indexOf(Object o)

代码示例：

int pos = list.indexOf("Item2");

检查列表是否为空

格式：

boolean isEntry();

代码示例：

int size = list.size();

检查是否包含指定元素

格式：

boolean contains(Object o)

代码示例：

boolean element = list.contains("Item5");

获取指定位置元素

格式：

E get(int index);

index 超出列表范围则抛出异常 IndexOutOfBoundsException，列表长度获取：

int size();

代码示例：

String item = list.get(0);

循环打印列表元素

代码示例：

for (String str : list) {
    System.out.println("Item is: " + str);
}

使用迭代器打印列表元素

格式：

Iterator<E> iterator();

代码示例：

for (Iterator<String> it = list.iterator(); it.hasNext();) {
    System.out.println("Item is: " + it.next());
}

设置指定位置元素

格式：

E set(int index, E element);

代码示例：

list.set(1, "NewItem");

移除指定位置元素或符合给定值的元素

格式：

E remove(int index);
boolean remove(Object element);

代码示例：

list.remove(0);
list.remove("Item3");

将列表转为数组

格式：

Object[] toArray();        // 转为对象数组
<T> T[] = toArray(T[] a);    // 转为指定类型的数组

代码示例：

String[] simpleArray = list.toArray(new String[list.size()]);