java8 統(tǒng)計字符串字母個數(shù)的幾種方法總結(推薦)

//方式1
  public static void letterCount1(String s) {
  	s=s.replaceAll(" +", "");
	   //1,轉換成字符數(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,獲取鍵所對應的值
		Integer value=tree.get(c[i]);
//		   反編譯：Integer value = (Integer)tree.get(Character.valueOf(c[i]));
	   //3,存儲判斷
		tree.put(c[i], value==null? 1:value+1);
	  }
	  
	  //如果要求結果格式：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(")");
	  }
	  //將sbu轉換為字符串
	  System.out.println(sbu.toString());
	}
   
  //方式2 使用流
  //這個在測試特殊字符,比如\  \n時,他的順序會不對,這個是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);
  	
  }
  
  //方式3 使用Collections.frequency
  //其實就是字符串變成集合存每個字串,把每個字串循環(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,沒有找到,則直接返回這個字符串
		// 2.比如qqqjava,末尾沒有其他字符,這時也不會分割,所以可以添加一個空格
		// 3.java11開頭沒有字符，沒有關系，自動空填充
		// 4.對于特殊字符,要注意使用轉義符
		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，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)計一個文本中單詞的個數(shù)
  public static void wordFileCount(String path) throws IOException{
  	//這里一開始字符串流
  	//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);
  }

public void testName() {
      System.out.println("a");
   }

    public void testName(String ... s) {
        //不傳參數(shù),s會默認初始化一個對象
     System.out.println("b");
  }