java8 streamList轉(zhuǎn)換使用的方法有哪些

Map<String, Object>; resultMap = lists
    .stream()
    .flatMap(map ->map.entrySet().stream())
    .collect(Collectors.toMap(e ->e.getKey(), e->e.getValue(),(a,b)->a)));

Map<String, Object> map = maps.stream()
    .map(Map::entrySet)
    .flatMap(Set::stream)
    .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,(a,b)->a)));

Map<String, Object>; resultMap = lists
    .stream()
    .collect(Collectors.toMap(Entry::getProtity, Entry::getProtity,(a,b)->a)));

//方式1
  public static void letterCount1(String s) {
   s=s.replaceAll(" +", "");
   //1,轉(zhuǎn)換成字符數(shù)組
   char c[]=s.toCharArray();
  
   Map<Character, Integer> tree=new TreeMap<Character, Integer>();
   for (int i = 0; i < c.length; i++) {
 //第一次：a,1
 //第二次：a,2 
   //2,獲取鍵所對(duì)應(yīng)的值
 Integer value=tree.get(c[i]);
   //3,存儲(chǔ)判斷
 tree.put(c[i], value==null&#63; 1:value+1);
   }
   System.out.println(tree);
 }
   
  //方式2 使用流
  //這個(gè)在測(cè)試特殊字符,比如\  \n時(shí),他的順序會(huì)不對(duì),這個(gè)是Map造成的
  //解決辦法使用TreeMap
  public static void letterCount2(String s) {
   s=s.replaceAll(" +", "");
   TreeMap<String, Long> result = Arrays.stream(s.split(""))
             .sorted()
//      .collect(Collectors.groupingBy(Function.identity(),Collectors.counting()));
       .collect(Collectors.groupingBy(Function.identity(),TreeMap::new,Collectors.counting()));
    System.out.println(result);
   
  }
  //或者
 public static void letterCount2_1(String s) throws Exception {
 s=s.replaceAll(" +", "");
 Stream<String> words = Arrays.stream(s.split(""));
 Map<String, Integer> wordsCount = words.collect(Collectors.toMap(k -> k, v -> 1,
                            (i, j) -> i + j));
 System.out.println(wordsCount);
 }
  
  //方式3 使用Collections.frequency
  //其實(shí)就是字符串變成集合存每個(gè)字串,把每個(gè)字串循環(huán)跟集合比較
  public static void letterCount3(String s) {
   s=s.replaceAll(" +", "");
   List<String> list=Arrays.asList(s.split(""));
   Map<String,Integer> map=new TreeMap<String, Integer>();
   for (String str : list) {
   map.put(str, Collections.frequency(list, str));
 }
   System.out.println(map);
  }
  
  //方式4
  public static void letterCount4(String s) {
   s=s.replaceAll(" +", "");
   String[] strs = s.split("");
   Map<String,Integer> map=new TreeMap<String, Integer>();
   for (String str : strs) {
   map.put(str, stringCount(s, str));
 }
   System.out.println(map);
  }
  
  //方式5
  public static void letterCount5(String s) {
   s=s.replaceAll(" +", "");
   String[] strs = s.split("");
   Map<String,Integer> map=new TreeMap<String, Integer>();
   for (String str : strs) {
   map.put(str, stringCount2(s, str));
 }
   System.out.println(map);
  }
  
  //巧用split
  public static int stringCount(String maxstr, String substr) {
 // 注意
 // 1.比如qqqq,沒(méi)有找到,則直接返回這個(gè)字符串
 // 2.比如qqqjava,末尾沒(méi)有其他字符,這時(shí)也不會(huì)分割,所以可以添加一個(gè)空格
 // 3.java11開(kāi)頭沒(méi)有字符，沒(méi)有關(guān)系，自動(dòng)空填充
 // 4.對(duì)于特殊字符,要注意使用轉(zhuǎn)義符
 int count = (maxstr + " ").split(substr).length - 1;
 // System.out.println("\"" + minstr + "\"" + "字符串出現(xiàn)次數(shù)：" + count);
 return count;
 }
 
  //如果要不區(qū)分大小寫(xiě)，則compile(minstr,CASE_INSENSITIVE)
 public static int stringCount2(String maxstr, String substr) {
 int count = 0;
 Matcher m = Pattern.compile(substr).matcher(maxstr);
 while (m.find()) {
  count++;
 }
    return count;
 }

 public static void wordStringCount(String s) {
   //這里開(kāi)始是字符串,分割后變成字符串流
    Map<String, Long> result = Arrays.stream(s.split("\\s+"))
                  .map(word -> word.replaceAll("[^a-zA-Z]", ""))
                        .collect(Collectors.groupingBy(Function.identity(),Collectors.counting()));
    System.out.println(result);   
  }

 //統(tǒng)計(jì)一個(gè)文本中單詞的個(gè)數(shù)
  public static void wordFileCount(String path) throws IOException{
   //這里一開(kāi)始字符串流
   //先分割
   //在變成字符流
   //在篩選
   Map<String, Long> result = Files.lines(Paths.get(path),Charset.defaultCharset())
            .parallel()
    //字符串流--分割--字符串流
   .flatMap(str->Arrays.stream(str.split(" +"))) 
   .map(word -> word.replaceAll("[^a-zA-Z]", ""))
   //去掉空
   .filter(word->word.length()>0) 
   .collect(Collectors.groupingBy(Function.identity(),Collectors.counting()));
   System.out.println(result);
  }
 //優(yōu)化:更精確的是根據(jù)非單詞來(lái)分組
  public static void wordFileCount0(String path) throws IOException{
   Map<String, Long> result = Files.lines(Paths.get(path),Charset.defaultCharset())
    .parallel()
    //字符串流--分割--字符串流
    .flatMap(str->Arrays.stream(str.split("[^a-zA-Z]+"))) 
    //去掉\n
    .filter(word->word.length()>0) 
    .collect(Collectors.groupingBy(Function.identity(),Collectors.counting()));
   System.out.println(result);
  }