Java 8 Collection stream Collectors.toMap

Question

Why this code is not compile for me?

I try to convert List to Map using stream and toMap option

List<CountryToPaymentMethodsDisplayRules>
   paymentMethodDisplayRulesByCountryList = 
       gatway.getCountryPaymentMethodsDisplayRulesByCountry();

Map<PaymentMethod, CountryToPaymentMethodsDisplayRules>
   countryToPaymentMethodsDisplayRulesMap = paymentMethodDisplayRulesByCountryList
       .stream()
       .collect(Collectors.toMap(type -> type.getCountryToPaymentMethodsDisplayRules().getPaymentMethod(),
                                 type -> type));

public interface PaymentMethod extends Serializable {
}

public enum PaymentMethodType implements PaymentMethod, Serializable {
}

public interface CountryToPaymentMethodsDisplayRules {
    public PaymentMethod getPaymentMethod();
}

public class CountryToPaymentMethodsDisplayRulesEntity implements CountryToPaymentMethodsDisplayRules, PersistentEntity<Long>, Serializable {
    @Type(type = "com.plimus.core.payment.PaymentMethodTypeUserType")
    @Column(name = "PAYMENT_TYPE")
    private PaymentMethod paymentMethod;
}

What is wrong here?

Well you've provided some code (which I've reformatted for you - please read the formatting help and avoid posting until the preview shows reasonable formatting) but you haven't said in what way it doesn't work... Ideally, rewrite this as a [mcve]. — Jon Skeet, Mar 17 '17 at 11:06
I can not find method getCountryToPaymentMethodsDisplayRules. Could you provide some information about this method? — Roma Khomyshyn, Mar 17 '17 at 11:07
Indeed, what *is* wrong here? Does it produce an exception? Does it produce an empty map? Does it run indefinitely? We may never know! — M. Prokhorov, Mar 17 '17 at 11:13

CraigR8806 · Answer 1 · 2017-03-17T16:16:35.637

7

You just need to provide the Collections.toMap() method with a method reference and an identity. Try this:

 Map<PaymentMethod, CountryToPaymentMethodsDisplayRules>
    countryToPaymentMethodsDisplayRulesMap = paymentMethodDisplayRulesByCountryList
    .stream()
    .collect(Collectors.toMap(CountryToPaymentMethodsDisplayRules::getPaymentMethod,x->x);

edited Mar 17 '17 at 16:16

answered Mar 17 '17 at 11:16

CraigR8806

1,584
13
21

score 0 · Answer 2 · answered Mar 17 '17 at 11:15

0

Found the problem thanks

Map<PaymentMethod, CountryToPaymentMethodsDisplayRules>
countryToPaymentMethodsDisplayRulesMap = paymentMethodDisplayRulesByCountryList
   .stream()
   .collect(Collectors.toMap(type -> type.getPaymentMethod(),
                             type -> type));

answered Mar 17 '17 at 11:15

Yaron Tzur

108
1
1
6

4

Do you really think that the finding, that calling a method that does not exist can be fixed by removing the method call, has any worth for future readers? – Holger Mar 17 '17 at 15:03

Java 8 Collection stream Collectors.toMap

2 Answers2

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