英文:
unchecked call to getDeclaredConstructor(Class
问题
Class c1 = Class.forName(theName)
return (CalculationFunction) c1.getDeclaredConstructor().newInstance();
但是我收到了这个警告：
unchecked call to getDeclaredConstructor(Class
英文:
I have this piece of code
Class c1 = Class.forName(theName)
return (CalculationFunction) c1.getDeclaredConstructor().newInstance();
but I have this warn:
unchecked call to getDeclaredConstructor(Class
答案1
得分: 1
`java.lang.Class`类是通用的，因此您需要对其进行参数化。因为您是根据类的名称进行操作，所以在编译时无法'知道'它是什么，因此实际上无法将其放入类型中。请尝试以下代码：
Class<?> c1 = Class.forName(theName);
return (CalculationFunction) c1.getDeclaredConstructor().newInstance();
请注意，除非将构造函数标记为可访问，否则此代码实际上不起作用，除非无参数构造函数是公共的，在这种情况下'getConstructor'更具惯性。上述代码要么毫无意义，要么有错误。
我认为您想要的更接近以下方式：
Class<?> c1 = Class.forName(theName);
Constructor<?> ctr = c1.getDeclaredConstructor();
ctr.setAccessible(true);
return (CalculationFunction) ctr.newInstance();
或者：
Class<?> c1 = Class.forName(theName);
return (CalculationFunction) c1.getConstructor().newInstance();
`j.l.Class`是通用的，要求您添加一些内容，否则会收到警告，但由于您不知道类型，而且已经进行了类型转换，通用性并没有太多作用；因此，`<?>` 将是合适的（而且您不能在那里放置其他任何内容，否则会收到更多警告）。
英文:
The java.lang.Class class is generified, so you need to parameterize it. Because you're going by the name of a class, there's no way to 'know' at compile time what it is, so it is not actually possibee to put in a type. Try this:
Class<?> c1 = Class.forName(theName);
return (CalculationFunction) c1.getDeclaredConstructor().newInstance();
note that this code doesn't actually work out unless you mark the constructor as accessible, unless the no-args constructor is public, in which case 'getConstructor' is more idiomatic. The above code is either uselessly obtuse, or buggy.
I think you intend something more along the lines of:
Class<?> c1 = Class.forName(theName);
Constructor<?> ctr = c1.getDeclaredConstructor();
ctr.setAccessible(true);
return (CalculationFunction) ctr.newInstance();
or:
Class<?> c1 = Class.forName(theName);
return (CalculationFunction) c1.getConstructor().newInstance();
j.l.Class, being generified, demands you add something or you get a warning, but because you don't know, and you're already casting, the generics isn't adding much; hence, <?> will be fine (and not that you can put anything else there without getting more warnings).
答案2
得分: 0
你可以使用 Class<?> 来避免这个错误。
英文:
You can use Class<?> to avoid this error.
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