判断逻辑有问题。我猜你是想要这种效果:
public static void main(String[] args) throws Exception {
Scanner sc = new Scanner(System.in);
String password1 = null;
boolean flag = true;
int length = 0;
System.out.println("请输入密码" + "(字符长度在6~18位之间)");//
do {
password1 = sc.nextLine();
if (null != password1 && !password1.isEmpty()) {
length = password1.length();
}
flag = (length < 6 || length > 18);
if (flag) {
System.err.println("密码长度不满足!(密码字符长度在6~18位之间)");
}
} while (flag);
System.out.println("恭喜您,密码设定成功");
System.out.println("设定密码为:" + password1);
sc.close();
}