这个 Holder<> 在 Java 中有什么作用？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/25777793/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
What does this Holder<> do in Java?
提问by Sparshith P
Can someone please explain this code?
有人可以解释一下这段代码吗？
public void getSupplierByZipCode(
@WebParam(name = "zip", targetNamespace = "http://www.webservicex.net/")
String zip,
@WebParam(name = "GetSupplierByZipCodeResult", targetNamespace = "http://www.webservicex.net/", mode = WebParam.Mode.OUT)
Holder<Boolean> getSupplierByZipCodeResult,
@WebParam(name = "SupplierDataLists", targetNamespace = "http://www.webservicex.net/", mode = WebParam.Mode.OUT)
Holder<SupplierDataList> supplierDataLists);
I've never seen Holderbefore in Java. What are Holder<Boolean>and Holder<SupplierDataList>in the function? Are they like outputs?? I need the supplier data list from this function.
我以前从未Holder在 Java 中见过。什么是Holder<Boolean>和Holder<SupplierDataList>在功能？他们喜欢输出吗？我需要此功能的供应商数据列表。
回答by user2864740
See Holder- The entire purpose is to "hold a value" while allowing side-effect modifications of itself(and thus change value it "holds").
参见Holder- 整个目的是“持有一个价值”，同时允许对其自身进行副作用修改（从而改变它“持有”的价值）。
The instance variable (value) representing the contained/"held" value can be reassigned; this is used to facilitate how [multiple] values are "returned" in the WS - through explicit modification of the holders supplied as parameters. (Note the usage of WebParam.Mode.OUTas well.)
value表示包含/“持有”值的实例变量 ( ) 可以重新分配；这用于促进 [多个] 值如何在 WS 中“返回” - 通过显式修改作为参数提供的持有者。（注意WebParam.Mode.OUTas的用法。）
This "extra layer" is required because Java is alwaysCall By Value; the Holder then effectively fakes a pointer-indirection (let's call it "reference-indirection"), as what might be done in C, which leads to Call By (Object) Sharingsemantics.
这个“额外的层”是必需的，因为 Java总是Call By Value；然后 Holder 有效地伪造了一个指针间接（让我们称之为“引用间接”），就像在 C 中可能做的那样，这导致调用（对象）共享语义。
Imagine:
想象：
// Outside WS function - setup parameters and invoke
String zip = "98682";
Holder<Boolean> result = new Holder<Boolean>();
getSupplierByZipCode(zip, result, ..);
// Then inside the function the Holder is modified and a new value
// is assigned to it's value member.
getSupplierByZipCodeResult.value = true;
// And outside again, the mutations are visibile still
if (result.value) {
// Yay!
}
Since strings are immutable and the zip is notwrapped in a Holder then the zip code cannot be changed (or "returned" by) the WS call.
由于字符串是不可变的并且 zip未包装在 Holder 中，因此 WS 调用无法更改（或“返回”）邮政编码。
See also:
也可以看看：
