How to collect result of a stream into an array of custom object in Java 8 [duplicate]

问题

This question already has answers here:

How to convert a Java 8 Stream to an Array? (9 answers)

Java stream toArray() convert to a specific type of array (2 answers)

Closed 8 months ago.

I have an List<TestBuilder> testBuilders; Test has a function build of type Test

I did testBuilders.stream().map(Test::build()).collect()

I want to collect above in array of Test i.e Test[]

I am not sure what would go in collect function

回答1:

Use the terminal operation Stream::toArray which packs the sequence of items into an array. However, you have to define a provided generator IntFunction<A[]> to allocate the type of returned array:

Test[] array = testBuilders.stream().map(Test::build()).toArray(size -> new Test[size]);

The lambda expression size -> new Test[size] should be replaced with a method reference:

Test[] array = testBuilders.stream().map(Test::build()).toArray(Test[]::new);

回答2:

You can use

whatever.stream().toArray(WhatEverClass[]::new);

to create an array for objects of type WhatEverClass based on "whatever" stream of objects of that type. Thus: no need to collect() anything.

来源：https://stackoverflow.com/questions/55927132/how-to-collect-result-of-a-stream-into-an-array-of-custom-object-in-java-8