统计指定内容的汉字个数：
String str = "北京欢迎你 hello welcome!";
int count=0;
Pattern pattern = Pattern.compile("[\u4e00-\u9fa5]");
char c[] = str.toCharArray();
for(int i=0;i<c.length;i++){
Matcher matcher = pattern.matcher(String.valueOf(c[i]));
if(matcher.matches()){
count++;
}
}
System.out.println(count);