有些方法找不到 Some method is undefined

[KitGavinx]

class: lambdasinaction.chap10.OperationsWithOptional
line 15 and line 18
The method or(() -> {}) is undefined for the type Optional

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class: lambdasinaction.chap10.OptionalMain
line 21
The method flatMap(Function<? super Optional,? extends Stream<? extends R>>) in the type Stream<Optional> is not applicable for the arguments (Optional::stream)

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class: lambdasinaction.chap6.Grouping
line 36
The method flatMapping(( dish) -> {}, toSet()) is undefined for the type Grouping

line 41
The method filtering(( dish) -> {}, toList()) is undefined for the type Grouping

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class: lambdasinaction.chap6.PartitionPrimeNumbers
line 36
The method takeWhile(( i) -> {}) is undefined for the type Stream

[manaatmoon]

I meet the same problems. The readme.md said this project should be based on JAVA 1.8, but actually the takeWhile is a new function for JAVA 1.9, and also source and target in the pom.xml are also 1.9, so i'm a little confused which java version should i use to run this project?

[xerZV]

@manaatmoon I've used Java 11.

[MABIY]

pom.xml compile plugin source and target all 1.9 , but the project of java8.

[NiceSeason]

I meet the same problems ,too

[DeepaAC]

any solution i am also facing same problem when giving 1.8

[warriorSL2016]

java11 is ok