https://blog.csdn.net/qq_39045534/article/details/79097864
https://blog.csdn.net/P90X_Liyuan/article/details/79573294
public static void countSubstring(){
//方法1:遍历法
String s1="abcdabc";
String s2="ab";
int count=0;
for(int i=0;s1.indexOf(s2)!=-1;i++){
count++;
s1=s1.substring(s1.indexOf(s2)+s2.length());
}
System.out.println(count); //2
//方法2:分割法
s1="abcdabc";
String[] arr=s1.split(s2);
int len=arr.length-1;
if(s1.endsWith(s2)) len++;
System.out.println(len); //2
}