Java8：使用流将一个地图转换为另一个地图

我需要将Java HashMap转换为TreeMap的实例（包括地图内容）

 HashMap src = ...; TreeMap dest = src.entrySet().stream() .filter( ... ) .collect(Collectors.toMap( ???, ???, ???, TreeMap::new)); 

我应该代替什么??? 使这段代码可编辑？

Answer 1

来自Collectors.toMap（…）javadoc ：

  * @param keyMapper a mapping function to produce keys * @param valueMapper a mapping function to produce values * @param mergeFunction a merge function, used to resolve collisions between * values associated with the same key, as supplied * to {@link Map#merge(Object, Object, BiFunction)} * @param mapSupplier a function which returns a new, empty {@code Map} into * which the results will be inserted 

例如：

 HashMap src = ...; TreeMap dest = src.entrySet().stream() .filter( ... ) .collect(Collectors.toMap(Map.Entry::getKey , Map.Entry::getValue, (a,b) -> a, TreeMap::new));