Function.apply-方法在未被覆盖时在自定义界面中执行什么操作？

Question

我无法理解以下示例代码中“apply”方法的用法。 apply 方法到底在做什么，因为它没有被覆盖？它显然返回结果 ValidationResult，但没有代码支持它。

public class Main {

    public static void main(String[] args) {
        
        Customer customer = new Customer("Alice", "alice@gmail.com", "0879546451", LocalDate.of(2000, 1, 1));
                
        ValidationResult result = CustomerRegistrationValidator
        .isEmailValid()
        .and(CustomerRegistrationValidator.isPhoneNumber())
        .and(CustomerRegistrationValidator.isAdult())
        .apply(customer);
        
        System.out.println(result);
    }
}

public interface CustomerRegistrationValidator extends Function<Customer, ValidationResult> {
    
    static CustomerRegistrationValidator isEmailValid() {
        return customer -> customer.getEmail().contains("@") ? ValidationResult.SUCCESS : ValidationResult.EMAIL_NOT_VALID;
    }
    
    static CustomerRegistrationValidator isPhoneNumber() {
        return customer -> customer.getPhoneNumber().contains("+08") ? ValidationResult.SUCCESS : ValidationResult.PHONE_NUMER_NOT_VALID;
    }
    
    static CustomerRegistrationValidator isAdult() {
        return customer -> Period.between(customer.getDob(), LocalDate.now()).getYears() > 16 ? ValidationResult.SUCCESS : ValidationResult.IS_NOT_AN_ADULT;
    }
    
    default CustomerRegistrationValidator and (CustomerRegistrationValidator other) {
        return customer -> {
            ValidationResult result = this.apply(customer);
            return result.equals(ValidationResult.SUCCESS) ? other.apply(customer) : result;
        };
    }
    
    enum ValidationResult {
        SUCCESS, PHONE_NUMER_NOT_VALID, EMAIL_NOT_VALID, IS_NOT_AN_ADULT;
    } 
}

Answer 1

What is the apply method doing exactly, since it's not overwritten?

取决于您从接口中选择的静态方法。在 isEmailValid 的情况下， apply 方法的主体是

customer.getEmail().contains("@") ? ValidationResult.SUCCESS : ValidationResult.EMAIL_NOT_VALID;

It's obviously returning the result ValidationResult, but there is no code to back it.

在那里，CustomerRegistrationValidator 实例由 lambda 定义。

想象一下你必须重写这个

static CustomerRegistrationValidator isEmailValid() {
  return new CustomerRegistrationValidator() {
    @Override
    public ValidationResult apply(Customer customer) {
      return customer.getEmail().contains("@") ? ValidationResult.SUCCESS : ValidationResult.EMAIL_NOT_VALID;
    }
  };
}

到 lambda 语法。你最终会得到你现在所拥有的。

Function.apply-方法在未被覆盖时在自定义界面中执行什么操作？

What does the Function.apply-Method do in a custom interface, when it's not overwritten?

java

functional-programming

interface

functional-interface