August 2020
Intermediate to advanced
483 pages
11h 24m
Chinese
Content preview from Head First Kotlin程序设计
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你现在的位置 4 263
集合
List
允许重复项
如你所知，使用
List
或是
MutableList
比使用数组更加灵
活。与数组不同，你可以明确选择集合是否为不可变，或者
其值是否可以被添加、移除、更新。
但是，在某些情况下，使用
List
（或
M
utableList
）并不是
很有效。
想象一下，你正在安排一顿和一群朋友的聚餐，你需要知道
有多少人参加以便预定餐桌。你可以使用
List
来记录，但有个
问题：
List
可
以有重复项。那么就有可能发生，在创建的朋友
List
中，某些朋友被列出两次：
在本章前面的内容中
，
我们讨论了
Kotlin
中不同类型的集合
。
你认
为哪种类型的集合最适合这种情况呢
？
但是如果想知道有多少个唯一的朋友在
List
中，你
不能简单地使用代码：
val friendList = listOf("Jim",
"Sue",
"Sue",
"Nick",
"Nick")
friendList.size
找出需要为多少人预定餐桌。因为
size
属性只认为
List
中有
5
个元素，它不关心其中的两个是重复的。
在这种情况下，我们需要使用不允许重复值存在的集合。那
么我们应该使用哪种类型的集合呢？
引用
引用
引用
0
1
2
String
“Jim”
String
“Sue”
String
“Nick”
val List<String>
引用
friend
List
引用
引用
3
4
该
List
的大小为
5
，
但
只有
3
个唯一的值
。
这里有三位朋友
：
Jim
、
Su
e
和
Nick
。
但
Su
e
和
Nick
被列
出两次
。
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.