java统计字符串中子字符串出现次数

package com.nafio.update;

import java.util.TreeMap;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Main {

public static void main(String[] args) {

System.out.println(finder("nidayededa","da"));
//da出现2次输出2
}
public static int finder(String source, String regexNew) {
String regex = "[a-zA-Z]+";
if (regexNew != null && !regexNew.equals("")) {
regex = regexNew;
}
Pattern expression = Pattern.compile(regex);
Matcher matcher = expression.matcher(source);
TreeMap<Object, Integer> myTreeMap = new TreeMap<Object, Integer>();
int n = 0;
Object word = null;
Object num = null;
while (matcher.find()) {
word = matcher.group();
n++;
if (myTreeMap.containsKey(word)) {
num = myTreeMap.get(word);
Integer count = (Integer) num;
myTreeMap.put(word, new Integer(count.intValue() + 1));
} else {
myTreeMap.put(word, new Integer(1));
}
}
return n;
}
}