让java中的setter返回“this”是好还是坏?
public Employee setName(String name){
this.name = name;
return this;
}
这个模式很有用，因为你可以像这样设置链:
list.add(new Employee().setName("Jack Sparrow").setId(1).setFoo("bacon!"));
而不是这样:
Employee e = new Employee();
e.setName("Jack Sparrow");
...and so on...
list.add(e);
.．.但这有点违背标准惯例。我认为这是值得的因为它可以让setter做一些其他有用的事情。我曾在一些地方看到过这种模式(例如JMock、JPA)，但它似乎并不常见，而且通常只用于定义良好的api，在这些api中这种模式随处可见。
更新:
我所描述的显然是有效的，但我真正想要的是一些关于这是否被普遍接受的想法，以及是否存在任何陷阱或相关的最佳实践。我知道Builder模式，但它比我所描述的要复杂一些——正如Josh Bloch所描述的，有一个用于对象创建的相关静态Builder类。
我更喜欢使用“with”方法:
public String getFoo() { return foo; }
public void setFoo(String foo) { this.foo = foo; }
public Employee withFoo(String foo) {
setFoo(foo);
return this;
}
因此:
list.add(new Employee().withName("Jack Sparrow")
.withId(1)
.withFoo("bacon!"));
警告:此withX语法通常用于为不可变对象提供“setter”，因此这些方法的调用者可能合理地期望它们创建新对象，而不是改变现有实例。也许更合理的措辞应该是:
list.add(new Employee().chainsetName("Jack Sparrow")
.chainsetId(1)
.chainsetFoo("bacon!"));
使用chainsetXyz()命名约定，几乎每个人都应该满意。
总结:
它被称为“流畅接口”或“方法链接”。
这不是“标准”Java，尽管你现在看到的越来越多(在jQuery中工作得很好)
它违反了JavaBean规范，因此它将与各种工具和库分开，特别是JSP构建器和Spring。
它可能会阻止JVM通常会做的一些优化
一些人认为它能清理代码，另一些人认为它“可怕”
还有一些没有提到的要点:
This violates the principal that each function should do one (and only one) thing. You may or may not believe in this, but in Java I believe it works well.
IDEs aren't going to generate these for you (by default).
I finally, here's a real-world data point. I have had problems using a library built like this. Hibernate's query builder is an example of this in an existing library. Since Query's set* methods are returning queries, it's impossible to tell just by looking at the signature how to use it. For example:
Query setWhatever(String what);
It introduces an ambiguity: does the method modify the current object (your pattern) or, perhaps Query is really immutable (a very popular and valuable pattern), and the method is returning a new one. It just makes the library harder to use, and many programmers don't exploit this feature. If setters were setters, it would be clearer how to use it.
