計算一個字符串中每一個字符出現的次數

import java.util.Map;
import java.util.TreeMap;

public class SetDemo7 {
	public static void main(String[] args) {
		String str = "aasdfasdgdifjgiosgsdofgbsmvbisdrthweuotpowsdnfgbvi";
		//Map<Character, Integer> map = new HashMap<Character, Integer>();
		//要想有順序的話,用下面這個TreeMap,         key存儲字符名,value存儲出現次數
		Map<Character, Integer> map = new TreeMap<Character, Integer>();		
		char[] charArray = str.toCharArray();//將String字符串轉換成字符數組
		//遍歷字符數組,循環的到每一個字符
		for (char ch : charArray) {
			//判斷當前字符是否在Map中的key存在
			if (map.containsKey(ch)) {
				//當前Map中的key包含該字符,此時取出該key對應的value的值加1,然後在放進去
				Integer old = map.get(ch);
				map.put(ch, old + 1);
			} else {
				//當前Map的key不包含該字符,把該字符存儲到Map中,設置value的初始值爲1
				map.put(ch, 1);
			}
		}
		System.out.println(map);
	}
}

打印結果:

{a=3, b=3, d=6, e=1, f=4, g=5, h=1, i=4, j=1, m=1, n=1, o=4, p=1, r=1, s=7, t=2, u=1, v=2, w=2}