【Java】统计字符串中每个字符出现的次数

package LearnJava6;import java.util.HashMap;import java.util.Scanner;import java.util.Set;//统计字符串中每个字符出现的次数public class HashMapDemo3 {public static void main(String[] args) {Scanner sc=new Scanner(System.in);System.out.println("请输入字符串:");String line = sc.nextLine();HashMap<Character,Integer> hm=new HashMap<Character,Integer>();//遍历字符串，得到每一个字符for (int i = 0; i < line.length(); i++) {char key = line.charAt(i);// 拿到的每一个字符作为键到HashMap中找对应的值Integer value = hm.get(key);if (value==null){//如果不存在就把该字符作为keyhm.put(key,1);}else {//如果存在就数量+1,然后重新存储该字符和值value++;hm.put(key,value);}}StringBuilder sb=new StringBuilder();Set<Character> keySet = hm.keySet();for (Character key:keySet){Integer value= hm.get(key);sb.append(key).append("(").append(value).append(")");}String result = sb.toString();System.out.println(result);}}

优化排序使用TreeMap

package LearnJava6;import java.util.HashMap;import java.util.Scanner;import java.util.Set;import java.util.TreeMap;//统计字符串中每个字符出现的次数public class HashMapDemo3 {public static void main(String[] args) {Scanner sc=new Scanner(System.in);System.out.println("请输入字符串:");String line = sc.nextLine();// HashMap<Character,Integer> hm=new HashMap<Character,Integer>();// TreeMap排序TreeMap<Character,Integer> hm=new TreeMap<Character,Integer>();//遍历字符串，得到每一个字符for (int i = 0; i < line.length(); i++) {char key = line.charAt(i);// 拿到的每一个字符作为键到HashMap中找对应的值Integer value = hm.get(key);if (value==null){//如果不存在就把该字符作为keyhm.put(key,1);}else {//如果存在就数量+1,然后重新存储该字符和值value++;hm.put(key,value);}}StringBuilder sb=new StringBuilder();Set<Character> keySet = hm.keySet();for (Character key:keySet){Integer value= hm.get(key);sb.append(key).append("(").append(value).append(")");}String result = sb.toString();System.out.println(result);}}