The following code returns the length of longest common substring from given two strings in Java. For cases of around 10^6 characters, it is still not fast enough to get the answer in a few seconds. Any suggestions for efficiency will be greatly appreciated!

int longestCommonSubstring(String s, String t){       int maxlength = 0; for(int i=0; i<s.length(); i++){     for(int j=0; j<t.length(); j++){         int count = 0;         int g = 0;         while(i+g<s.length() && j+g<t.length()){             if(t.charAt(j+g)==s.charAt(i+g)){                 count++;                 maxlength = Integer.max(count, maxlength);             }             else{                 count = 0;                       }             g++;         }     } } return maxlength; 

}