你没考虑两个字符串一样长的问题，修改成一下就行 import java.util.*; public class Main { public static void main(String [] args) { Scanner sc = new Scanner(System.in); String s1 = sc.nextLine(); String s2 = sc.nextLine(); System.out.println(getPublicStr(s1, s2)); } public static int getPublicStr( String s1, String s2) { int count = 0; for (int i = 0; i < s1.length(); i++) { for (int j = s1.length(); j > i; j--) { if (s2.contains(s1.substring(i, j))) { count = Math.max(j - i, count); } } } return count; } }