串模式匹配BF算法的java实现

如下代码，进行串模式匹配BF算法的java实现

 class BF{
    public int bF(char S[],char T[]){
        int i=0,j=0,index=0;
        while(S[i]!='\0'&&T[j]!='\0'){
            if(S[i] == T[j]){
                i++;
                j++;
            }else{
                index++;
                i = index;
                j = 0;
            }
        }
        if(T[j]!='\0'){
            return index+1;
        }else{
            return 0;
        }
    }
}
public class String_matching {
    public static void main(String[] args) {
        BF bf = new BF();
        String str1 = "ababacbc";
        String str2 = "bacb";
        char c1[] = str1.toCharArray();
        char c2[] = str2.toCharArray();
        bf.bF(c1, c2);
    }
}

运行后抛出如下异常

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4
at BF.bF(String_matching.java:4)
at String_matching.main(String_matching.java:28)

请问这是为什么？