Question

我对Java还是很陌生，我正在尝试创建一组通过映射中的lambda表达式获取的对象。基本上，我从映射（lambda表达式）中获取一个值，并运行它以获取布尔值。但是，在表达式上运行.apply时出现错误。有想法该怎么解决这个吗？任何帮助表示赞赏。

        Map<String, Predicate<IndexSub>> order_function = new HashMap<>();
        order_function.put("AlternativesValues", x -> false);
        order_function.put("AlternativesConstituent", x -> x.getCloseCons());
        order_function.put("EquityValues", x -> false);
        order_function.put("EquityCloseConstituent", x -> x.getCloseCons());
        order_function.put("EquityOpenConstituent", x -> x.getOpenCons());
        order_function.put("FixedValues", x -> false);
        order_function.put("FixedReturns", x -> x.getCloseCons());
        order_function.put("FixedStatistics", x -> x.getOpenCons());

        //getCloseCons and getOpenCons return true/false    

        Set<String> orderable_sub = new HashSet<String>();

        for (IndexSub s : tenant_subscriptions) {
                                 //DataProduct is a string
            if (order_function.get(DataProduct).apply(s) == true){
                orderable_sub.add(s.getIndexId());
            }

        }

Answer 1

Predicate功能界面具有test()方法，而不是module.exports.verifyStandardMetadata = data => { .... }：

apply()

Answer 2

由于您似乎将相同的谓词应用于tenant_subscriptions中的所有元素，因此可以使用流：

Predicate<IndexSub> p = order_function.get(dataProduct);

if( p == null ) {
  //handle that case, e.g. set a default predicate or skip the following part
}

//this assumes tenant_subscriptions is a collection, if it is an array use Arrays.stream(...) or Stream.of(...)
Set<String> orderable_sub = tenant_subscriptions.stream() //create the stream
                               .filter(p) //apply the predicate
                               .map(IndexSub::getIndexId) //map all matching elements to their id
                               .collect(Collectors.toSet()); //collect the ids into a set

如何在地图上运行作为值的Lambda表达式

2 个答案: