Java 通用：未经检查的演员表

Question

I must use Java 17 (LTS).

The following code works fine, but I have the following warning:

Unchecked cast...

I am not able to get rid of this warning, whatever I do with my classes.

The class where the warning appears:

public abstract class Parser<T> {

    protected static <T> Parser<T> build(Class<T> parserType, InputArgGroup arguments) {
        Parser<T> parser;
        if (parserType.isAssignableFrom(Name.class)) {
            parser = (Parser<T>) new NameParser();    <- UNCHECKED CAST: x.NameParser to x.Parser<T>
        } else {
            parser = (Parser<T>) new AddressParser(); <- UNCHECKED CAST: x.AddressParser to x.Parser<T>
        }

        parser.hasTitle(arguments.hasTitle());
        parser.hasHeader(arguments.hasHeader());
        parser.setDateTimePattern(arguments.getDateTimePattern());
        ...
        return parser;
    }

    ... common methods ...

    public abstract List<T> parse(String file);
}

Parser 1:

public class NameParser extends Parser<Name> {
    @Override
    public List<Name> parse(String file) {
        System.out.println("parse name CSV");
        return null;
    }
}

Parser 2:

public class AddressParser extends Parser<Address> {
    @Override
    public List<Address> parse(String file) {
        System.out.println("parse address CSV");
        return null;
    }
}

Test:

public class Aaa {
    public Aaa() {
        var addressParser = Parser.build(Address.class, ...);
        var nameParser = Parser.build(Name.class, ...);

        List<Address> addresses = addressParser.parse("addresses.csv");
        List<Name> names = nameParser.parse("names.csv");

    }

    public static void main(String[] args) {
        new Aaa();
    }
}

Any help is appreciated.

Answer 1

It's only a warning to let you know the compiler can't guarantee the cast won't fail at runtime. You know it will work, but the compiler isn't sophisticated enough to figure it out too.

Suppress the warning with an annotation.

@SuppressWarnings("unchecked")
protected static <T> Parser<T> build(Class<T> parserType, InputArgGroup arguments) {
   // ...
}

Using this annotation is not circumventing the compiler - you got a warning and after analysis and running tests you verified the cast will never actually fail at runtime and you adding this annotation to record that analysis and finding.