Skip to content

修复ArrayList扩容机制的问题 #1017

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 1 commit into from
Nov 18, 2020
Merged

修复ArrayList扩容机制的问题 #1017

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
2 changes: 1 addition & 1 deletion notes/Java 容器.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -132,7 +132,7 @@ private static final int DEFAULT_CAPACITY = 10;

#### 2. 扩容

添加元素时使用 ensureCapacityInternal() 方法来保证容量足够，如果不够时，需要使用 grow() 方法进行扩容，新容量的大小为 `oldCapacity + (oldCapacity \>\> 1)`，也就是旧容量的 1.5 倍。
添加元素时使用 ensureCapacityInternal() 方法来保证容量足够，如果不够时，需要使用 grow() 方法进行扩容，新容量的大小为 `oldCapacity + (oldCapacity >> 1)`，也就是旧容量的 1.5 倍左右，（oldCapacity 为偶数就是 1.5 倍，oldCapacity为奇数就是 1.5 倍-0.5）。奇偶不同，比如 ：8+8/2 = 12, 13+13/2=19，如果是奇数的话会丢掉小数。

扩容操作需要调用 `Arrays.copyOf()` 把原数组整个复制到新数组中，这个操作代价很高，因此最好在创建 ArrayList 对象时就指定大概的容量大小，减少扩容操作的次数。

Expand Down