Java语言是否具有委托特性,类似于c#对委托的支持?
当前回答
没有,没有。
你可以通过使用反射来获得你可以调用的Method对象来达到同样的效果,另一种方法是创建一个带有单个“invoke”或“execute”方法的接口,然后实例化它们来调用你感兴趣的方法(即使用匿名内部类)。
你可能还会发现这篇文章很有趣/有用:一个Java程序员看c#委托(@blueskyprojects.com)
其他回答
简短的故事:没有。
Introduction The newest version of the Microsoft Visual J++ development environment supports a language construct called delegates or bound method references. This construct, and the new keywords delegate and multicast introduced to support it, are not a part of the JavaTM programming language, which is specified by the Java Language Specification and amended by the Inner Classes Specification included in the documentation for the JDKTM 1.1 software. It is unlikely that the Java programming language will ever include this construct. Sun already carefully considered adopting it in 1996, to the extent of building and discarding working prototypes. Our conclusion was that bound method references are unnecessary and detrimental to the language. This decision was made in consultation with Borland International, who had previous experience with bound method references in Delphi Object Pascal. We believe bound method references are unnecessary because another design alternative, inner classes, provides equal or superior functionality. In particular, inner classes fully support the requirements of user-interface event handling, and have been used to implement a user-interface API at least as comprehensive as the Windows Foundation Classes. We believe bound method references are harmful because they detract from the simplicity of the Java programming language and the pervasively object-oriented character of the APIs. Bound method references also introduce irregularity into the language syntax and scoping rules. Finally, they dilute the investment in VM technologies because VMs are required to handle additional and disparate types of references and method linkage efficiently.
通过类路径上的安全镜像,你可以得到类似c#委托和事件的东西。
来自项目README的例子:
Java中的委托!
Delegate.With1Param<String, String> greetingsDelegate = new Delegate.With1Param<>();
greetingsDelegate.add(str -> "Hello " + str);
greetingsDelegate.add(str -> "Goodbye " + str);
DelegateInvocationResult<String> invocationResult =
greetingsDelegate.invokeAndAggregateExceptions("Sir");
invocationResult.getFunctionInvocationResults().forEach(funInvRes ->
System.out.println(funInvRes.getResult()));
//prints: "Hello sir" and "Goodbye Sir"
事件
//Create a private Delegate. Make sure it is private so only *you* can invoke it.
private static Delegate.With0Params<String> trimDelegate = new Delegate.With0Params<>();
//Create a public Event using the delegate you just created.
public static Event.With0Params<String> trimEvent= new Event.With0Params<>(trimDelegate)
看看这个SO的答案。
我知道这篇文章很旧了,但是Java 8增加了lambdas和函数接口的概念,即任何接口都只有一个方法。它们一起提供了与c#委托类似的功能。查看这里获得更多信息,或者只是谷歌Java Lambdas。 http://cr.openjdk.java.net/~briangoetz/lambda/lambda-state-final.html
根据您的意思,您可以使用策略模式达到类似的效果(传递一个方法)。
而不是像这样的一行声明一个命名方法签名:
// C#
public delegate void SomeFunction();
声明一个接口:
// Java
public interface ISomeBehaviour {
void SomeFunction();
}
对于方法的具体实现,定义一个实现行为的类:
// Java
public class TypeABehaviour implements ISomeBehaviour {
public void SomeFunction() {
// TypeA behaviour
}
}
public class TypeBBehaviour implements ISomeBehaviour {
public void SomeFunction() {
// TypeB behaviour
}
}
然后在c#中使用SomeFunction委托的地方,使用ISomeBehaviour引用:
// C#
SomeFunction doSomething = SomeMethod;
doSomething();
doSomething = SomeOtherMethod;
doSomething();
// Java
ISomeBehaviour someBehaviour = new TypeABehaviour();
someBehaviour.SomeFunction();
someBehaviour = new TypeBBehaviour();
someBehaviour.SomeFunction();
使用匿名内部类,您甚至可以避免声明单独的命名类,几乎可以将它们视为真正的委托函数。
// Java
public void SomeMethod(ISomeBehaviour pSomeBehaviour) {
...
}
...
SomeMethod(new ISomeBehaviour() {
@Override
public void SomeFunction() {
// your implementation
}
});
这可能只应该在实现非常特定于当前上下文并且不会从重用中受益时使用。
当然,在Java 8中,这些基本变成了lambda表达式:
// Java 8
SomeMethod(() -> { /* your implementation */ });
不,Java没有这个惊人的特性。但是您可以使用观察者模式手动创建它。这里有一个例子: 用java编写c#委托
推荐文章
- Java 8接口方法中不允许“同步”的原因是什么?
- 如何找到Java堆大小和内存使用(Linux)?
- 使用Enum实现单例(Java)
- RabbitMQ与通道和连接之间的关系
- buildSessionFactory()配置方法在Hibernate中已弃用?
- Spring MVC -如何获得所有的请求参数在一个地图在Spring控制器?
- 如何在Java中按两个字段排序?
- 文件之间的差异。路径中的分隔符和斜杠
- 在方法参数中使用NotNull注释
- Spring MVC中处理可选参数的@RequestParam
- Tomcat:如何查找正在运行的Tomcat版本?
- “java”、“javaw”和“javaws”之间有什么区别?
- 将Date对象转换为日历对象
- 在Java中保存最后N个元素的大小有限的队列
- 如何运行一个类从Jar不是主类在其清单文件