java - 用于打印客户对象的数组列表

Question

如何使用 Customer 类型的数组列表(有 2 个子类，非成员和成员)通过比较打印出所有客户对象？换句话说，我想检查某个索引处的数组列表，并检查它是否是非成员或成员对象，并相应地打印输出。这是我的代码:

ArrayList<Customer> customerList = new ArrayList<Customer>();

for(int i = 0; i < customerList.size(); i++)
{
    if(customerList.get(i) == // nonmember)                     
    {
        // want to use toString in NonMemberCustomer class
    }
    else // member
    {       
        // use toString in MemberCustomer class to print output.
    }
}

public String toString()    
{
    return "\nMember Customer:" + super.toString() +
           "Collected Points:\t" + pointsCollected + "\n\n";
}

public String toString()
{
    return "NonMember Customer:" + super.toString() +
           "Visit Fee:\t\t" + visitFee + "\n\n";
}

Answer 1

使用 Customer 作为参数类型声明您的数组列表:

// So that the polymorphism would work
List<Customer> customerList = new ArrayList<>();

其次，您不需要 if/else 语句来打印对象各自的 toString()；只需覆盖每个类中的toString()方法& polymorphism将从那里拿走它。

for(int i =0; i < customerList.size();i++) {
    // Implicit call to the toString() method
    System.out.println(customerList.get(i)); 
}

类(class):(例如)

class Customer {
    // properties & methods

    @Override
    public String toString() {
        System.out.println("The customer's toString !");
    }
}

class Member extends Customer {
    // properties & methods

    @Override
    public String toString() {
        System.out.println("The member's toString !");
    }
}

class NonMember extends Customer {
    // properties & methods

    @Override
    public String toString() {
        System.out.println("The nonmember's toString !");
    }
}