java8 统计字符串字母个数的几种方法总结(推荐)

//方式1  public static void letterCount1(String s) {  	s=s.replaceAll(" +", "");	   //1,转换成字符数组	  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,获取键所对应的值		Integer value=tree.get(c[i]);//		   反编译：Integer value = (Integer)tree.get(Character.valueOf(c[i]));	   //3,存储判断		tree.put(c[i], value==null? 1:value+1);	  }	  	  //如果要求结果格式：a(5)b(4)c(3)d(2)e(1)	  StringBuilder sbu=new StringBuilder();	  for(Character key:tree.keySet()){		Integer count=tree.get(key);		sbu.append(key).append("(").append(count).append(")");	  }	  //将sbu转换为字符串	  System.out.println(sbu.toString());	}     //方式2 使用流  //这个在测试特殊字符,比如/  /n时,他的顺序会不对,这个是Map造成的  //解决办法使用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);  	  }    //方式3 使用Collections.frequency  //其实就是字符串变成集合存每个字串,把每个字串循环跟集合比较  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,没有找到,则直接返回这个字符串		// 2.比如qqqjava,末尾没有其他字符,这时也不会分割,所以可以添加一个空格		// 3.java11开头没有字符，没有关系，自动空填充		// 4.对于特殊字符,要注意使用转义符		int count = (maxstr + " ").split(substr).length - 1;		// System.out.println("/"" + minstr + "/"" + "字符串出现次数：" + count);		return count;	}  //如果要不区分大小写，则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) {  	//这里开始是字符串,分割后变成字符串流    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);  	  }

 //统计一个文本中单词的个数  public static void wordFileCount(String path) throws IOException{  	//这里一开始字符串流  	//先分割  	//在变成字符流  	//在筛选  	 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);  }

public void testName() {      System.out.println("a");   }    public void testName(String ... s) {        //不传参数,s会默认初始化一个对象     System.out.println("b");  }