Java8编译错误"inference variable D has incompatible bounds"

Question

Java 8 不会编译下面的代码（Java 7 过去可以很好地编译）。我对错误有所了解，但不知道如何修复我的代码，你能帮我吗？

错误在这一行：

spec = spec.and(toSpecification(range));

我显然需要更改传递的参数，或者重写 toSpecification 代码，但还没有找到任何可行的方法。

public class RangeSpecification {

    public static <E> Specification<E> andRangeIfSet(Specification<E> spec, final List<Range<E, ?>> ranges) {
        for (Range<E, ?> range : ranges) {
            if (range.isSet()) {
                spec = spec.and(toSpecification(range));
            }
        }
        return spec;
    }

    public static <E, D extends Comparable<? super D>> Specification<E> toSpecification(final Range<E, D> range) {
        Validate.isTrue(range.isSet(), "You must provide a usable criterion");
        return new Specification<E>() {
            /**
             * 
             */
            private static final long serialVersionUID = 1L;

            @Override
            public Predicate toPredicate(Root<E> root, CriteriaQuery<?> query, CriteriaBuilder builder) {
                Predicate rangePredicate = null;

                if (range.isBetween()) {
                    rangePredicate = builder.between(root.get(range.getField()), range.getFrom(), range.getTo());
                } else if (range.isFromSet()) {
                    rangePredicate = builder.greaterThanOrEqualTo(root.get(range.getField()), range.getFrom());
                } else if (range.isToSet()) {
                    rangePredicate = builder.lessThanOrEqualTo(root.get(range.getField()), range.getTo());
                }

                if (rangePredicate != null) {
                    if (!range.isIncludeNullSet() || range.getIncludeNull() == Boolean.FALSE) {
                        return rangePredicate;
                    } else {
                        return builder.or(rangePredicate, builder.isNull(root.get(range.getField())));
                    }
                }

                // Pas de range
                if (range.getIncludeNull() == Boolean.TRUE) {
                    return builder.isNull(root.get(range.getField()));
                }

                if (range.getIncludeNull() == Boolean.FALSE) {
                    return builder.isNotNull(root.get(range.getField()));
                }

                throw new IllegalStateException("Vous devez passer un critère exploitable !!!(ne devrait jamais ce produire ici)");
            }
        };
    }
}

完整的错误是：

/D:/xxx/repository/support/RangeSpecification.java:[23,33] method toSpecification in class xxx.repository.support.RangeSpecification cannot be applied to given types;
required: xxx.repository.support.Range
found: xxx.repository.support.Range
reason: inference variable D has incompatible bounds
equality constraints: capture#1 of ?
upper bounds: java.lang.Comparable

我需要编译的代码！ Eclipse 构建没有错误，但使用 Java 1.8.191 编译时出错。非常感谢。

Answer 1

其实代码应该是这样的：

public static <E, D extends Comparable<? super D>> Specification<E> andRangeIfSet(Specification<E> spec, final List<Range<E, D>> ranges) {
    for (Range<E, D> range : ranges) {
        if (range.isSet()) {
            spec = spec.and(toSpecification(range));
        }
    }
    return spec;
}

我无法编译和测试它，但缺少参数 "D" 的绑定。一般来说，尽量避免通配符“？”只要有可能。

请注意，您必须重构该方法的所有调用方。

Java8编译错误"inference variable D has incompatible bounds"

Java 8 compilation error "inference variable D has incompatible bounds"

java

type-bounds