ArrayList学习笔记！！！

package com.ethjava;

import java.util.*;

public class Arraylistlianxi {

    public static void main(String args[]) {
        // 创建一个空的数组链表对象list，list用来存放String类型的数据
        ArrayList list = new ArrayList();
        ArrayList list2=new ArrayList<>(7);//如果你需要创建一个指定初始容量的数组链表，你可以这样做
        list2.add(1);
        // 增加元素到list对象中
        list.add("Item1");//位置0
        list.add("Item2");//位置1
        list.add(2, "Item3"); // 位置2，此条语句将会把“Item3”字符串增加到list的第3个位置。
        list.add("Item4");//位置3
        list.add(2,"yxf");//将位置2的item3挤走，放上yxf，原来的内容往后移
        list.add("Item2");
        // 显示数组链表中的内容
        System.out.println("The arraylist contains the following elements: "
                + list);
        //打印结果：The arraylist contains the following elements: [Item1, Item2, yxf, Item3, Item4]
        //The arraylist contains the following elements: [Item1, Item2, yxf, Item3, Item4, item2]


        // 检查元素的位置
        int pos = list.indexOf("Item2");
        System.out.println("The index of Item2 is: " + pos);//The index of Item2 is: 1
        //只能检查到第一个Item2的位置 1

        int pos2=list.lastIndexOf("Item2");
        System.out.println("the last appear position: "+pos2);
        //int lastIndexOf(Object o);返回元素在链表中最后一次出现的位置，如果返回-1，表示链表中没有这个元素
        //the last appear position: 5

        // 检查数组链表是否为空
        boolean check = list.isEmpty();
        System.out.println("Checking if the arraylist is empty: " + check);//list不为空，打印false
        boolean check2=list2.isEmpty();
        System.out.println(check2);//是空的，就打印true,

        //Checking if the arraylist is empty: false
        //true


        // 获取链表的大小
        int size = list.size();
        System.out.println("The size of the list is: " + size);
        int size2 = list2.size();
        System.out.println(size2);//空的list，就打印0
        //The size of the list is: 6
        //0

        // 检查数组链表中是否包含某元素
        boolean element = list.contains("Item5");//不包含
        System.out.println("Checking if the arraylist contains the object Item5: "
                        + element);//Checking if the arraylist contains the object Item5: false

        boolean yxfelement = list.contains("yxf");
        System.out.println(yxfelement);//包含就打印true


        // 获取指定位置上的元素
        String item = list.get(0);
        System.out.println("The item is the index 0 is: " + item);
        Integer item2 =  list2.get(0);
        System.out.println(item2);//输出1

        //这里注意返回的数据类型，要与创建时相同。。。


        // 遍历arraylist中的元素

        // 第1种方法: 循环使用元素的索引和链表的大小
        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));
        }
        //Retrieving items with loop using index and size list
        //Index: 0 - Item: Item1
        //Index: 1 - Item: Item2
        //Index: 2 - Item: yxf
        //Index: 3 - Item: Item3
        //Index: 4 - Item: Item4
        //Index: 5 - Item: item2


        // 第2种方法:使用foreach循环
        System.out.println("Retrieving items using foreach loop");
        for (String str : list) {
            System.out.println("Item is: " + str);
        }
        //etrieving items using foreach loop
        //Item is: Item1
        //Item is: Item2
        //Item is: yxf
        //Item is: Item3
        //Item is: Item4
        //Item is: item2


        // 第三种方法:使用迭代器
        // hasNext(): 返回true表示链表链表中还有元素
        // next(): 返回下一个元素
        System.out.println("Retrieving items using iterator");
        for (Iterator it = list.iterator(); it.hasNext();) {
            System.out.println("Item is: " + it.next());
        }
        //Retrieving items using iterator
        //Item is: Item1
        //Item is: Item2
        //Item is: yxf
        //Item is: Item3
        //Item is: Item4
        //Item is: item2

        for(Iterator it=list2.iterator();it.hasNext();){
            System.out.println("Item is : "+it.next());
        }
        //Item is : 1


        // 替换元素
        list.set(1, "NewItem");
        System.out.println("The arraylist after the replacement is: " + list);
        //The arraylist after the replacement is: [Item1, NewItem, yxf, Item3, Item4, item2]

        // 移除元素
        // 移除第0个位置上的元素
        list.remove(0);
        System.out.println("The arraylist after the replacement is: " + list);
        //The arraylist after the replacement is: [NewItem, yxf, Item3, Item4, item2]


        // 移除第一次找到的 "Item3"元素
        list.remove("Item3");//后面加某个元素

        System.out.println("The final contents of the arraylist are: " + list);
        //The final contents of the arraylist are: [NewItem, yxf, Item4, item2]

        list.remove(0);//删除第0位置的元素
        System.out.println("The final contents of the arraylist are: " + list);
        //The final contents of the arraylist are: [yxf, Item4, item2]




        // 转换 ArrayList 为 Array
        String[] simpleArray = list.toArray(new String[list.size()]);
        //list.toArray获取一个数组，数组中所有元素是链表中的元素.（即将链表转换为一个数组）
        System.out.println("The array created after the conversion of our arraylist is: "
                + Arrays.toString(simpleArray));
        //he array created after the conversion of our arraylist is: [yxf, Item4, item2]
        System.out.println("The array created after the conversion of our arraylist is: "
                +simpleArray);
        //The array created after the conversion of our arraylist is: [Ljava.lang.String;@28a418fc
        //直接打印数组只会输出数组的地址


    }
}

c参考：https://www.cnblogs.com/ShallByeBye/p/8419027.html