如何在Java中使用方法参数来实现多个接口? [英] How can I require a method argument in Java to implement multiple interfaces?
问题描述
在Java中执行此操作是合法的:
It's legal to do this in Java:
void spew(Appendable x)
{
x.append("Bleah!\n");
}
我该怎么做(语法不合法):
How can I do this (syntax not legal):
void spew(Appendable & Closeable x)
{
x.append("Bleah!\n");
if (timeToClose())
x.close();
}
我希望尽可能强制调用者使用可附加和可关闭,无需特定类型。有多个标准类可以执行此操作,例如BufferedWriter,PrintStream等
I would like if possible to force callers to use objects that are both Appendable and Closeable, without requiring a specific type. There are multiple standard classes that do this, e.g. BufferedWriter, PrintStream, etc.
如果我定义自己的界面
interface AppendableAndCloseable extends Appendable, Closeable {}
自实现Appendable的标准类以来不起作用和Closeable不实现我的接口AppendableAndCloseable(除非我不理解Java以及我认为我做...空接口仍然在其超级接口之外添加唯一性)。
that won't work since the standard classes that implement Appendable and Closeable do not implement my interface AppendableAndCloseable (unless I don't understand Java as well as I think I do... empty interfaces still add uniqueness above and beyond their superinterfaces).
我能想到的最接近的是做以下其中一项:
The closest I can think of is to do one of the following:
-
选择一个界面(例如可追加),并使用运行时测试来确保参数是
instanceof
其他参数。缺点:在编译时没有遇到问题。
pick one interface (e.g. Appendable), and use runtime tests to ensure the argument is an
instanceof
the others. Downside: problem not caught at compile time.
需要多个参数(捕获编译时正确但看起来很笨):
require multiple arguments (catches compile-time correctness but looks dorky):
void spew(Appendable xAppend, Closeable xClose)
{
xAppend.append("Bleah!\n");
if (timeToClose())
xClose.close();
}
推荐答案
你可以用泛型来做:
public <T extends Appendable & Closeable> void spew(T t){
t.append("Bleah!\n");
if (timeToClose())
t.close();
}
实际上你的语法几乎正确。
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