这是一个创建于 2228 天前的主题，其中的信息可能已经有所发展或是发生改变。
看到有代码是如下这样写的，
class A{
private A(B b){...}
public static A of(B b) { return new A(b); }
}
这样写的好处是什么呢？ 如果这是一种好的风格或者手段的话，是否有一种获取途径，来了解好的风格或者手段？
 |
1
GTim 2018-09-27 18:10:44 +08:00
单例模式了解下，嗯，其实，好处不仅仅是单例
|
 |
4
linshuang 2018-09-27 18:46:34 +08:00
也是第一次看见，或许可以把 of 替换成一个句子来达到代码具备更强的语义的目的. 就模式而言，至少我没见过这种。
例如 Parent p = Parent.withChildren(children) |
 |
5
maninfog 2018-09-27 18:52:38 +08:00 via Android
@GTim 这个每次都是 new 和单例的确无关阿
这种写法估计是为了利用静态方法名充当注释的作用，个人感觉。 |
 |
6
icris 2018-09-27 18:54:57 +08:00  1
参考示例：BigInteger.valueOf(1)
|
 |
7
lululau 2018-09-27 18:59:31 +08:00
new A(b) VS A.of(b)
|
|
8
lululau 2018-09-27 19:00:05 +08:00
8 个字符 VS 7 个字符，效率提升了
|
 |
9
wbgbg 2018-09-27 19:02:26 +08:00 1
Effective Java 第一条 考虑使用静态工厂方法替代构造方法
这里的主要优点就是有方法名来表示含义 |
 |
10
sutra 2018-09-27 19:02:41 +08:00
可以参考 Instant.ofXXX() 的实现，可以看出来它并不是每次都 new 一个对象出来，有些是直接用的共享的对象。
|
 |
11
CasualYours 2018-09-27 19:06:57 +08:00 via Android
Optional 类就是这种写法，好处就是代码语义更直接吧。
|
 |
12
Cbdy 2018-09-27 19:08:13 +08:00 1
Effective Java 第三版第二章第一节有详细介绍
我简单摘录一下： ### 优点 One advantage of static factory methods is that, unlike constructors, they have names. A second advantage of static factory methods is that, unlike constructors, they are not required to create a new object each time they ’ re invoked. A third advantage of static factory methods is that, unlike constructors, they can return an object of any subtype of their return type. A fourth advantage of static factories is that the class of the returned object can vary from call to call as a function of the input parameters. A fifth advantage of static factories is that the class of the returned object need not exist when the class containing the method is written. ### 缺点 The main limitation of providing only static factory methods is that classes without public or protected constructors cannot be subclassed. A second shortcoming of static factory methods is that they are hard for programmers to find. ### 一些常见的静态构造方法 **from**: A type-conversion method that takes a single parameter and returns a corresponding instance of this type, for example: ```java Date d = Date.from(instant); ``` **of**: An aggregation method that takes multiple parameters and returns an instance of this type that incorporates them, for example: ```java Set<Rank> faceCards = EnumSet.of(JACK, QUEEN, KING); ``` **valueOf**: A more verbose alternative to from and of, for example: ```java BigInteger prime = BigInteger.valueOf(Integer.MAX_VALUE); ``` **instance** or **getInstance**: Returns an instance that is described by its parameters (if any) but cannot be said to have the same value, for example: StackWalker luke = StackWalker.getInstance(options); **create** or **newInstance**: Like instance or getInstance, except that the method guarantees that each call returns a new instance, for example: ```java Object newArray = Array.newInstance(classObject, arrayLen); ``` |
|
13
CasualYours 2018-09-27 19:09:39 +08:00 via Android
@GTim 不是单机例，of 静态方法每次都返回新的实例。
|
 |
14
Raymon111111 2018-09-27 19:29:57 +08:00
这是工厂, 了解一下工厂模式即可.
|
 |
15
lowzoom 2018-09-28 01:05:47 +08:00
class A 体现不出这个写法的精髓，要 interface A
|
 |
16
bk201 2018-09-28 09:20:49 +08:00
我认为是方便链式调用
类似 a.of(b).add(c).avg() |
Select Language