问题描述
使用Java泛型,我尝试实现一个通用的控制台输入法。
Using Java Generics, I tried to implement a generic console input method.
public static <T> T readFromInput(String message, Class<?> c) throws Exception{
System.out.println(message);
Scanner scanner = new Scanner(System.in);
try {
if(c == Integer.class)
return (T) Integer.valueOf(scanner.nextInt());
if(c == String.class)
return (T) scanner.nextLine();
if(c == Double.class)
return (T) Double.valueOf(scanner.nextDouble());
if(c == Float.class)
return (T) Float.valueOf(scanner.nextFloat());
} catch (InputMismatchException e) {
throw new Exception(e);
}
return null;
}
我有一个警告类型安全:从Integer到T 。除了@SuppressWarnings,是否可以避免此警告?
I'm having a warning "Type safety: Unchecked cast from Integer to T". Aside from @SuppressWarnings, is it possible to avoid this warning?
有更好的方法来实现我的方法吗?提前感谢
Are there better ways to implement my method? Thanks in advance
推荐答案
您可以改用 Class#cast
,但应该留下一些注释,因为即使 cast
不创建警告,如果不可能转换,它可能在运行时抛出ClassCastException。
You can use the Class#cast
method instead, but should leave some comments, because even though cast
does not create a warning, it can throw a ClassCastException at runtime if the cast is not possible.
public static <T> T readFromInput(String message, Class<T> c) throws Exception{
System.out.println(message);
Scanner scanner = new Scanner(System.in);
try {
if(c == Integer.class)
// the next cast to Integer is safe
return c.cast(Integer.valueOf(scanner.nextInt()));
if(c == String.class)
// the next cast to String is safe
return c.cast(scanner.nextLine());
if(c == Double.class)
// the next cast to Double is safe
return c.cast(Double.valueOf(scanner.nextDouble()));
if(c == Float.class)
// the next cast to Float is safe
return c.cast(Float.valueOf(scanner.nextFloat()));
} catch (InputMismatchException e) {
throw new Exception(e);
}
return null;
}
请注意,我稍微更改了方法签名 - c $ c> Class< T> 而不是 Class<?>
,以保证 Class
实例与type参数一致。
Note that I've changed the method signature slightly - it should be Class<T>
and not Class<?>
to guarantee, that the Class
instance is consistent with the type parameter.
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