Java统计一个字符串在另外一个字符串出现次数的方法

package me.chunsheng.javatest;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
 * Created by wei_spring on 16/10/11.
 * <p>
 * 统计一个字符串在另外一个字符串出现的次数
 * 正则匹配的方法,前提字符串不是特殊字符串
 * eg:finder("adadadadauuada","ada") 这样会统计不准确的.
 * 另外一个遍历的解决了上面那种情况.
 * 两者时间如下(纳秒为单位): 正则明显耗时,正则本就不是统计用的!!!
 * finder:3
 * finderTime:1579549
 * getCount:4
 * getCountTime:34506
 */
public class SubStringCount {
  public static void main(String[] args) {
    System.out.println("编程小技巧测试结果：");
    long current1 = System.nanoTime();
    System.out.println("finder:" + finder("adadadadauuada","ada"));
    System.out.println("finderTime:" + (System.nanoTime() - current1));
    long current2 = System.nanoTime();
    System.out.println("getCount:" + getCount("adadadadauuada","ada"));
    System.out.println("getCountTime:" + (System.nanoTime() - current2));
  }
  public static int getCount(String source,String sub) {
    int count = 0;
    int length = source.length() - sub.length();
    for (int i = 0; i < length; i++) {
      String sourceBak = source.substring(i,i + sub.length());
      int index = sourceBak.indexOf(sub);
      if (index != -1) {
        count++;
      }
    }
    return count;
  }
  public static int finder(String source,String regexStr) {
    String regex = "[a-zA-Z]+";
    if (regexStr != null && !regexStr.equals("")) {
      regex = regexStr;
    }
    Pattern expression = Pattern.compile(regex);
    Matcher matcher = expression.matcher(source);
    int n = 0;
    while (matcher.find()) {
      n++;
    }
    return n;
  }
}