一个经典的Map+正则表达式练习题：给定一个带其他文字的字母字符串，求出各个字符有多少个？

package com.test;

import java.util.HashMap;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Test {
public static void main(String[] args) {
String str = "aaaaaannnnnnnnvvvva阿森纳反复vvvvasd阿萨德vvdddddddddddffffffasdadasdasdadasdasdasdasd";
//首先要先把中文去掉，使用正则表达式获取字母；
               String s1 = getString(str);
char[] ch = s1.toCharArray();
Map<Character,Integer> map = new HashMap<Character,Integer>();
for (int i = 0; i < ch.length; i++) {
if(map.containsKey(ch[i])){
int n = map.get(ch[i])+1;
map.put(ch[i], n);
}else{
map.put(ch[i],1);
}
}
System.out.println(map);
}

public static String getString(String str){
Pattern p = Pattern.compile("[a-zA-Z]");
StringBuffer buf = new StringBuffer();
char[] c = str.toCharArray();
for (int i = 0; i < c.length; i++) {
Matcher m = p.matcher(c[i]+"");
if(m.find()){
buf.append(c[i]);
}
}
return buf.toString();
}

}