计算字符串出现的次数

package com.lyis.test; public class App { public static void main(String[] args) { String str = "asdfasdfasdf "; int index = -1; int num = 0; do { index = str.indexOf("sd", index + 1); if (index >= 0) { num++; } } while (index >= 0); System.out.println(num); } }