这一题应该要怎么做，求解答。

这里需要声明两个类,一个YouKe 和一个 Test 类

class YouKe {
  private int age;
  private String name;

  public YouKe() {
      Scanner scanner = new Scanner(System.in);
      System.out.println("请输入年龄：");
      age = scanner.nextInt();
      System.out.println("请输入姓名：");
      name = scanner.next();
  }

  public int getAge() {
      return age;
  }

  public String getName() {
      return name;
  }

  public int buy(int age) {
      if (age >= 18) {
          return 50;
      } else if (age > 12 && age < 18) {
          return 25;
      } else if (age > 0 && age <= 12) {
          return 0;
      } else {
          System.out.println("输入的年龄非法");
          return 0;
      }
  }
}

public class Test {
  public static void main(String[] args) {
      YouKe youKe = new YouKe();
      int fare = youKe.buy(youKe.getAge());
      System.out.println(youKe.getName() + "的票价为：" + fare);
  }
}

• 输入的年龄等于零或者小于零，buy方法返回的值为0