BF java 修改一下，上课没听懂😭😭

import java.util.Scanner;
public class Main {
public static void main(String[]args) {
Scanner in = new Scanner(System.in);
System.out.print("主串"+"子串");
String S=in.next();
String T=in.next();
char[] s=S.toCharArray();
char[] t=T.toCharArray();
for(int i=0;i<=t.length-s.length;i++) {
int j=0;
while(j
i++;j++;
}
if(j==t.length){
System.out.println("succss");
}
}
}
}

问题是什么？

 public static void main(String[] args)  {
            Scanner in = new Scanner(System.in);
            System.out.print("主串"+"子串");
            String S=in.next();
            String T=in.next();
            char[] s=S.toCharArray();
            char[] t=T.toCharArray();
            int j=0;
            for(int i=0;i<s.length; ) {
                if(s[i]==t[j]){
                    i++; j++;
                }else{
                     i = i - j + 1; 
                     j = 0; 
                }
                if(j==t.length){
                    System.out.println(i - j);
                }
                }
      
            }