声纳问题 - 参数必须为非空，但被标记为可为空

Question

我已经写了这个谓词，而声纳正在抱怨它。我不确定如何解决此违规问题。请帮忙：

import com.google.common.base.Predicate;

import java.util.Map;
public final class FooPredicate {

    private FooPredicate(){}

    public static Predicate<Map.Entry<Long,Long>> isFirstElement(final Long o) {
        return new Predicate<Map.Entry<Long,Long>>() {
            @Override
            public boolean apply(Map.Entry<Long,Long> foo) { 
                return foo.getKey().equals(o);
            }
        };
    }
}

它在抱怨apply方法的Foo参数。

Dodgy - Parameter must be nonnull but is marked as nullable
foo must be nonnull but is marked as nullable

apply 方法被定义为可以为空，我对此无能为力。 Sonar 和 Guava 不是在打架吗？

> boolean apply(@Nullable
>             T input)
> 
> Returns the result of applying this predicate to input. This method is
> generally expected, but not absolutely required, to have the following
> properties:
> 
>     Its execution does not cause any observable side effects.
>     The computation is consistent with equals; that is, Objects.equal(a, b) implies that predicate.apply(a) ==
> predicate.apply(b)). 
> 
> Throws:
>     NullPointerException - if input is null and this predicate does not accept null arguments

Answer 1

你正在做foo.getKey()。如果foo 为null，则会抛出NullPointerException，但您并未声明foo 不能为null。

在使用之前检查 foo 是否为空。

if (foo != null) {
   return foo.getKey().equals(o);
} else {
   return null;
}