通过map集合统计每个字符出现的次数

public class ADemo {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入字符串");
        String str = sc.next();
        toMap(str);


    }
    public static void toMap(String str){
        Map<Character,Integer> m = new HashMap<>();
        char ch;
        for (int i = 0; i < str.length(); i++) {
            ch = str.charAt(i);
            if(m.keySet().contains(ch)){
                m.put(ch,m.get(ch)+1); //可以覆盖原来的值。
            }else{
                m.put(ch,1);
            }
        }
        for (Character key : m.keySet()) {
            System.out.println(key+"出现的次数："+m.get(key));
        }
    }