求两个字符串中最长公共子串 ——java

public class TestStr2 {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        System.out.println("请输入两个字符串：");
        String str1 = sc.nextLine();
        String str2 = sc.nextLine();

        System.out.println(TestStr2.printMaxChild(str1,str2));
    }
    public static String printMaxChild(String str1,String str2){
        int flag = 0;
        String MaxStr = str1.length() > str2.length() ? str1 : str2;
        String MinStr = str1.length() > str2.length() ? str2 : str1;

        int minStrLen = MinStr.length();
        String[] strs = new String[minStrLen];
        for(int i = 0; i < minStrLen; i++){
            for(int x = 0, y = minStrLen - i;  y <= minStrLen;  x++, y++){

                String subStr = MinStr.substring(x,y);

                if(MaxStr.contains(subStr)){
                   return subStr;
                }
            }
        }
        return null;
    }
}