求一简单的正则表达式,用来验证用户的密码

要求：至少包含一个数字，一个小写字母，一个大写字母，长度至少是6.
比如：
123ABC false
123abc false
123Abc true
12aBc false

public static void main(String[] args) {
String pattern = "(?=.*[A-Z])(?=.*[a-z])(?=.*[0-9])[a-zA-Z0-9]*";

    System.out.println("123".matches(pattern));
    System.out.println("123A".matches(pattern));
    System.out.println("Aa123".matches(pattern));
    System.out.println("123Ab".matches(pattern));
    System.out.println("123b".matches(pattern));
}