optional | 易学教程

Is there some way to specify a custom deserializer for a type that is nested inside an Optional for Jackson?

阅读更多关于 Is there some way to specify a custom deserializer for a type that is nested inside an Optional for Jackson?

问题 I have some types which need to be handled with their own special deserializers and serializers, but how do I instruct Jackson to use them when the type is nested inside an Optional? I am using the JDK8Module which works great for any type not needing any special handling. The @JsonDeserialize and @JsonSerialize annotations don't seem to have any way to apply to the value inside an Optional when they are used on an Optional field: @JsonDeserialize(?????) Optional<SpecialType> myField 回答1: The

Best Practice using an Array of Strings with NSUserDefault

阅读更多关于 Best Practice using an Array of Strings with NSUserDefault

问题 I'm having a bit trouble saving an array of strings to userDefaults. I have an Array of strings declaired in a class, with a property observer ment to sync to userDefaults. Furthermore, I want the array to be limited to a maximum of 5 Strings. let userDefaults = NSUserDefaults.standardUserDefaults() var suggestions: [String]! { didSet { var arrayEnd = suggestions.count if arrayEnd >= 5 { arrayEnd = 4 } let newArray = Array(suggestions[0...arrayEnd]) userDefaults.setObject(newArray, forKey:

Chaining of Java Optional map and orElse (if-else-style)

阅读更多关于 Chaining of Java Optional map and orElse (if-else-style)

问题 Is there an elegant and streaming way in Java to say "map this Optional to another Optional with a computed value if the value exists, else return an empty Optional"? I thought of something like: Optional<Float> amount = ...; Optional<MonetaryAmount> myAmount = amount .map(theAmount -> FastMoney.of(theAmount, "EUR")).orElse(Optional.empty()); But this is not possible. The solution I came up with is somewhat verbose and not streaming-like: Optional<Float> amount = ...; Optional<MonetaryAmount>

debian下普通用户操作systemd服务

阅读更多关于 debian下普通用户操作systemd服务

【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> 问题描述：使用普通账号test通过systemctl启动系统服务提示需要输入root密码：解决方案：根据上面提示得知权限由polkit进行管理，对应的是org.freedesktop.systemd1.policy这个配置文件下的manae-units动作进入/usr/share/polkit-1/actions/org.freedesktop.systemd1.policy，将对应manae-units的defaults中的授权全部改为yes，然后执行systemctl restart polkit重启polkit <defaults> <allow_any>yes</allow_any> <allow_inactive>yes</allow_inactive> <allow_active>yes</allow_active> </defaults> 下图为权限可选的配置参数 defaults This element is used to specify implicit authorizations for clients. Elements that can be used inside defaults include: allow_any Implicit authorizations

Can we use Optionals in Android programming?

阅读更多关于 Can we use Optionals in Android programming?

问题 I have been reading about the Optional type in Java 8. I want to implement in some of my Android code. But does the Dalvik machine for the latest versions of Android (5.1 and 6) implement everything in Java 8? I'm still running Java 7 with the Eclipse and Android Studio installed on my computers. 回答1: You can use StreamSupport lib which adds support for the new Streams API and as a side effect it has Optional . For gradle use: compile "net.sourceforge.streamsupport:streamsupport:1.5.1" 回答2:

Can we use Optionals in Android programming?

阅读更多关于 Can we use Optionals in Android programming?

Java 8 Optional

阅读更多关于 Java 8 Optional

问题 I want to check if a particular object size is greater than 0. If it is greater than 0 then I want to create an optional object, if not then I want to return an Optional empty. This is the long version of the java code: if(fooA.size>0) { return Optional.of(new Foo()); } else { return Optional.empty(); } Is there any way to compact this into one line using java 8's optional library? 回答1: Is there any way to compact this into one line using java 8's optional library? If you insist on using the

Optional in orElse-Branch throws Exception [duplicate]

阅读更多关于 Optional in orElse-Branch throws Exception [duplicate]

问题 This question already has an answer here : Java 8's orElse not working as expected (1 answer) Closed 3 years ago . So I'm working with Optionals and came across a strange behaviour. I want to know if this is really an intendet "feature" or something...odd... Here is the given example: I've got a method with an Optional in whose orElse I want to evaluate an other optional. If the other Optional is not present, I'll raise an IllegalArgumentException: firstOptionalVar.orElse(secondOptionalVar

Getopt optional arguments?

阅读更多关于 Getopt optional arguments?

问题 I have a program where you enter an option -d and then whether or not you supply a non-optional argument after the option, do something. Heres my code: #include <stdio.h> #include <getopt.h> #include <stdlib.h> #define OPT_LIST "d::" int main (int argc, char *argv[]) { int c; char string[] = "blah"; while ((c = getopt (argc, argv, OPT_LIST)) != -1) { switch (c) { case 'd': printf("%s\n", optarg); break; case '?': fprintf(stderr, "invalid option\n"); exit(EXIT_FAILURE); } } } So if you enter a

Using Color As Optional Parameter In a function within a class

阅读更多关于 Using Color As Optional Parameter In a function within a class

问题 How can I declare an optional color parameter in some function or sub, as if I do that in the normal way (I mean to give some default color for that optional parameter) as the vb.net compiler complains that there is some error in that code. How do I resolve this issue. Sample code below: Public Shared Function SomeFunction(ByVal iParam As Integer, Optional ByVal oColor As Color = Color.Black) End Function The compiler does not accept '=Color.Black' 回答1: MSDN says about Optional Parameters for