java8 find the first occurrence of the string twice letter java8 stream programming

Using functional programming stream is processed java8

1. To achieve separation of the letters

map the entire string as a word stream processing

Map<String[], Long> collect14 = Stream.of("hello word how are you")
                .map(o -> o.split(""))
//                .flatMap(Arrays::stream)
                .collect(Collectors.groupingBy(o -> o, Collectors.counting()));
 System.out.println(JSONObject.toJSONString(collect14));

输出：{["h","e","l","l","o"," ","w","o","r","d"," ","h","o","w"," ","a","r","e"," ","y","o","u"]:1}

2. To achieve the letter string repetition frequency statistics by convection flatMap flattening process (see flatMap with different map java8 stream programmed point 6 illustrates a)

Map <String, Long> collect14 Stream.of = ( "Hello Word How are you" ) 
                .map (O -> o.split ( "" )) 
                .flatMap (Arrays, :: Stream) obtained above with // the large brackets word stream into a character stream 
                .collect (Collectors.groupingBy (O -> O, Collectors.counting ())); 
        System.out.println (JSONObject.toJSONString (collect14));

输出：{" ":4,"a":1,"r":2,"d":1,"u":1,"e":2,"w":2,"h":2,"y":1,"l":2,"o":4}

3. The map of the entry into stream, to map the filter kv

String collect14 = Stream.of("hello word how are you")
                .map(o -> o.split(""))
                .flatMap(Arrays::stream)
                .collect(Collectors.groupingBy(o -> o, Collectors.counting()))
                .entrySet()
                .stream()
                .filter(o -> o.getValue() == 2)
                .limit(1)
                .map(o -> o.getKey())
                .collect(Collectors.joining());
        System.out.println(collect14);

Output: r